View source for Tyrannosaurus

{{Short description|Genus of Late Cretaceous theropod}}
{{Redirect|T. rex|other uses|T. rex (disambiguation)}}
{{Featured article}}
{{pp-vandalism|small=yes}}
{{Use American English|date=April 2021}}
{{Use mdy dates|date=November 2025}}
{{Automatic taxobox
| fossil_range = [[Late Cretaceous]]<br />(late [[Maastrichtian]]), {{Fossil range|earliest=77|69|66}} Possible middle [[Campanian]] record
| image = Tyrannosaurus Rex Holotype.jpg
| image_upright = 1.15
| image_caption = Reconstruction of the ''T. rex'' [[Type (biology)|type specimen]] at the [[Carnegie Museum of Natural History]]
| display_parents = 
| taxon = Tyrannosaurus
| authority = [[Henry Fairfield Osborn|Osborn]], 1905
| type_species = {{Extinct}}'''''Tyrannosaurus rex'''''
| type_species_authority = Osborn, 1905
| subdivision_ranks = Other species<!--Do not add T. imperator, T. regina, T bataar, or T. zhuchengensis. These are controversial species that are discussed in the article body.-->
| subdivision = * {{Extinct}}'''''T. mcraeensis'''''? {{Small|Dalman et al., [[2024 in archosaur paleontology|2024]]}}
* [[#Additional species|See text]]
| synonyms = {{Collapsible list|bullets = true
 |title=<small>Genus synonymy</small>
|''Dinotyrannus'' <br /><small>Olshevsky, Ford & Yamamoto, 1995</small>
|''Dynamosaurus'' <br /><small>Osborn, 1905</small>
|''Manospondylus'' <br /><small>[[Edward Drinker Cope|Cope]], 1892</small>
|''[[Stygivenator]]''? <br /><small>Olshevsky, Ford & Yamamoto, 1995</small>
}}
{{Collapsible list|bullets = true
 |title=<small>Species synonymy</small>
|''[[Aublysodon amplus]]''? <br /><small>[[Othniel Charles Marsh|Marsh]], 1892</small>
|''[[Deinodon amplus]]''? <br /><small>(Marsh, 1892) Hay, 1902</small>
|''[[Manospondylus amplus]]''? <br /><small>(Marsh, 1892) Olshevsky, 1978</small>
|''[[Stygivenator amplus]]''? <br /><small>(Marsh, 1892) Olshevsky, Ford & Yamamoto, 1995</small>
|''[[Tyrannosaurus amplus]]''? <br /><small>(Marsh, 1892) Hay, 1930</small>
|''[[Aublysodon cristatus]]''? <br /><small>Marsh, 1892</small>
|''[[Deinodon cristatus]]''? <br /><small>(Marsh, 1892) Hay, 1902</small>
|''[[Stygivenator cristatus]]''? <br /><small>(Marsh, 1892) Olshevsky, Ford & Yamamoto, 1995</small>
|''Ornithomimus grandis'' <br /><small>Marsh, 1890</small>
|''Manospondylus gigas'' <br /><small>[[Edward Drinker Cope|Cope]], 1892</small>
|''Dynamosaurus imperiosus'' <br /><small>Osborn, 1905</small>
|''Tyrannosaurus imperiosus'' <br /><small>(Osborn, 1905) Swinton, 1970</small>
|''Albertosaurus'' "megagracilis" <br /><small>Paul, 1988a (nomen nudum)</small>
|''Dinotyrannus megagracilis'' <br /><small>Olshevsky, Ford & Yamamoto, 1995</small>
|''Aublysodon molnaris''? <br /><small>Paul, 1988a</small>
|''Aublysodon molnari''? <br /><small>Paul, 1988a emend Paul, 1989</small>
|''Stygivenator molnari''? <br /><small>(Paul, 1988a emend Paul, 1989) Olshevsky, Ford & Yamamoto, 1995</small>
}}
}}

'''''Tyrannosaurus''''' ({{IPAc-en|t|ᵻ|ˌ|r|æ|n|ə|ˈ|s|ɔː|r|ə|s|,_|t|aɪ|-}}){{Efn|name=title|{{Lit|tyrant lizard}}; {{Etymology|grc|''{{Wikt-lang|grc|τύραννος}}'' ({{Grc-transl|τύραννος}})|tyrant||''{{Wikt-lang|grc|σαῦρος}}'' ({{Grc-transl|σαῦρος}})|lizard}}}} is a [[genus]] of large [[theropoda|theropod]] [[dinosaur]]. The [[type species]] '''''Tyrannosaurus rex''''' ({{Lang|la|rex}} meaning 'king' in [[Latin]]), often shortened to '''''T. rex''''' or colloquially '''t-rex''', is one of the best represented theropods. It lived throughout what is now western [[North America]], on what was then an island continent known as [[Laramidia]]. ''Tyrannosaurus'' had a much wider range than other [[Tyrannosauridae|tyrannosaurids]]. [[Fossil]]s are found in a variety of [[geological formations]] dating to the late [[Maastrichtian]] [[Age (geology)|age]] of the late [[Cretaceous]] [[Period (geology)|period]], 69 to 66&nbsp;[[mya (unit)|million years ago]], with isolated specimens possibly indicating an earlier origin in the middle [[Campanian]] age. It was one of the last known members of the tyrannosaurids and among the last non-[[Bird|avian]] dinosaurs to exist before the [[Cretaceous–Paleogene extinction event]].

Like other tyrannosaurids, ''Tyrannosaurus'' was a [[biped]]al [[carnivore]] with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, the forelimbs of ''Tyrannosaurus'' were short but unusually powerful for their size, and they had two clawed digits. The most complete specimen measures {{cvt|12.3|-|12.4|m}} in length, but according to most modern estimates, ''Tyrannosaurus'' could have exceeded sizes of {{cvt|13|m}} in length, {{cvt|3.7|-|4|m}} in hip height, and {{cvt|8.8|t}} in mass. Although some other theropods might have rivaled or exceeded ''Tyrannosaurus'' in [[dinosaur size|size]], it is still among the largest known land predators, with its estimated bite force being the largest among all terrestrial animals. By far the largest carnivore in its environment, ''Tyrannosaurus rex'' was most likely an [[apex predator]], preying upon [[hadrosaur]]s, juvenile armored herbivores like [[ceratopsia]]ns and [[ankylosaur]]s, and possibly [[sauropod]]s. Some experts have suggested the dinosaur was primarily a [[scavenger]]. The question of whether ''Tyrannosaurus'' was an apex predator or a pure scavenger was among the longest debates in [[paleontology]]. Most paleontologists today accept that ''Tyrannosaurus'' was both a predator and a scavenger.

Some [[Specimens of Tyrannosaurus|specimens of ''Tyrannosaurus rex'']] are nearly complete skeletons. [[Soft tissue]] and [[protein]]s have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of the animal's biology, including its life history and [[biomechanics]]. The feeding habits, [[physiology]], and potential speed of ''Tyrannosaurus rex'' are a few subjects of debate. Its [[Taxonomy (biology)|taxonomy]] is also controversial. The Asian ''[[Tarbosaurus bataar]]'' is very closely related to ''Tyrannosaurus'' and has sometimes been seen as a species of this genus. Several North American tyrannosaurids have been [[synonym (biology)|synonymized]] with ''Tyrannosaurus'', while some ''Tyrannosaurus'' specimens have been proposed as distinct species. The validity of these species, such as the more recently discovered '''''T. mcraeensis''''', is contentious.

''Tyrannosaurus'' has been one of the best-known dinosaurs since the early 20th century. Science writer [[Riley Black]] has called it the "ultimate dinosaur". Its fossils have been a popular attraction in museums and has appeared in media like ''[[Jurassic Park]]''.

==History of research==
{{see also|Specimens of Tyrannosaurus|l1=Specimens of ''Tyrannosaurus''}}

===Earliest finds===
[[File:AMNH 3982 Manospondylus.jpg|alt=|left|thumb|[[Type (biology)|Type specimen]] (AMNH 3982) of ''Manospondylus gigas'']]
A tooth from what is now documented as a ''Tyrannosaurus rex'' was found in July 1874 upon [[South Table Mountain (Colorado)]] by [[Jarvis Hall (Colorado)]] student Peter T. Dotson under the auspices of [[Arthur Lakes]] near [[Golden, Colorado]].<ref>{{Cite news|title=The Colorado Transcript|date=July 8, 1874|via=www.coloradohistoricnewspapers.org}}</ref> In the early 1890s, [[John Bell Hatcher]] collected postcranial elements in eastern [[Wyoming]]. The fossils were believed to be from the large species ''[[Ornithomimus|Ornithomimus grandis]]'' (now ''[[Deinodon]]'') but are now considered ''T. rex'' remains.<ref name="quinlanetal2007" />

In 1892, [[Edward Drinker Cope]] found two vertebral fragments of a large dinosaur. Cope believed the fragments belonged to an "agathaumid" ([[Ceratopsidae|ceratopsid]]) dinosaur, and named them ''Manospondylus gigas'', meaning "giant porous vertebra", in reference to the numerous openings for blood vessels he found in the bone.<ref name="quinlanetal2007">{{Cite journal |last1=Breithaupt |first1=B. H. |last2=Southwell |first2=E. H. |last3=Matthews |first3=N. A. |date=October 15, 2005 |title=In Celebration of 100 years of ''Tyrannosaurus rex'': ''Manospondylus gigas'', ''Ornithomimus grandis'', and ''Dynamosaurus imperiosus'', the Earliest Discoveries of ''Tyrannosaurus rex'' in the West |url=http://gsa.confex.com/gsa/2005AM/finalprogram/abstract_96150.htm |journal=Abstracts with Programs; 2005 Salt Lake City Annual Meeting |publisher=[[Geological Society of America]] |volume=37 |issue=7 |page=406 |archive-url=https://archive.today/20120530024000/http://gsa.confex.com/gsa/2005AM/finalprogram/abstract_96150.htm |archive-date=May 30, 2012 |access-date=October 8, 2008|issn=0016-7592}}</ref> The ''M. gigas'' remains were, in 1907, identified by Hatcher as those of a theropod rather than a ceratopsid.<ref>{{Cite journal |last=Hatcher |first=J. B. |year=1907 |title=The Ceratopsia |url=https://archive.org/stream/TheCeratopsia/Musgs-1907-hatcherEtAl-theCeratopsiaLkUsaPart1Monograph#page/n111 |journal=Monographs of the United States Geological Survey |volume=49 |pages=113–114|issn=0886-7550}}</ref>

[[Henry Fairfield Osborn]] recognized the similarity between ''Manospondylus gigas'' and ''T. rex'' as early as 1917, by which time the second vertebra had been lost. Owing to the fragmentary nature of the ''Manospondylus'' vertebrae, Osborn did not synonymize the two genera, instead considering the older genus indeterminate.<ref name="osborn1917">{{Cite journal |last=Osborn |first=H. F. |author-link=Henry Fairfield Osborn |year=1917 |title=Skeletal adaptations of ''Ornitholestes'', ''Struthiomimus'', ''Tyrannosaurus'' |journal=Bulletin of the American Museum of Natural History |volume=35 |issue=43 |pages=733–771 |hdl=2246/1334}}</ref> In June 2000, the [[Black Hills Institute]] found around 10% of a ''Tyrannosaurus'' skeleton ([[Black Hills Institute|BHI]] 6248) at a site that might have been the original ''M. gigas'' locality.<ref name="larson2008">{{Cite book |title=''Tyrannosaurus rex'', The Tyrant King |url=https://archive.org/details/tyrannosaurusrex00plar |url-access=limited |last=Larson |first=N. L. |publisher=Indiana University Press |year=2008 |isbn=978-0-253-35087-9 |editor-last=Larson |editor-first=P. |location=Bloomington, IN |pages=[https://archive.org/details/tyrannosaurusrex00plar/page/n16 1]–55 |chapter=One hundred years of ''Tyrannosaurus rex'': the skeletons |editor-last2=Carpenter |editor-first2=K.}}</ref> While Larson initially considered this specimen as the same animal as the ''M. gigas'' holotype and suggested that it would take priority over ''T. rex'', other researchers including Christopher Brochu remained skeptical that the name ''T. rex'' would be abandoned.<ref name=McTavish2000>{{cite web|author=McTavish, B.|date=July 10, 2000|title=The dinosaur formerly known as Tyrannosaurus rex?|url=https://www.tampabay.com/archive/2000/07/10/the-dinosaur-formerly-known-as-tyrannosaurus-rex/|access-date=October 18, 2025}}</ref> In 2003, Brochu further argued that although both taxa probably represent the same species, it is impossible to demonstrate that the specimen discovered by the Black Hills Institute represents the same animal as ''M. gigas'' due to the poor preservation of the ''M. gigas'' holotype; additionally, following the 2000 [[International Code of Zoological Nomenclature]] amendment, a name in popular usage like ''T. rex'' has priority over a name with technical priority but not used as a valid name in formal literature after the year 1899 for over fifty years like ''M. gigas''.<ref name="brochu2003"/><ref>{{cite web|title=Article 23. Principle of Priority|website=code.iczn.org|url=https://code.iczn.org/validity-of-names-and-nomenclatural-acts/article-23-principle-of-priority/?frame=1|access-date=November 17, 2025}}</ref>

===Skeleton discovery and naming===
[[File:Tyrannosaurus skeleton.jpg|thumb|Outdated skeletal restoration by [[William Diller Matthew|William D. Matthew]] from 1905, published alongside Osborn's description paper]]
[[Barnum Brown]], assistant curator of the [[American Museum of Natural History]], found the first partial skeleton of ''T. rex'' in eastern Wyoming in 1900. Brown found another partial skeleton in the [[Hell Creek Formation]] in Montana in 1902, comprising approximately 34 fossilized bones.<ref name="osborn1905" /> Writing at the time Brown said "Quarry No. 1 contains the femur, pubes, humerus, three vertebrae and two undetermined bones of a large Carnivorous Dinosaur not described by [[Othniel Charles Marsh|Marsh]].&nbsp;... I have never seen anything like it from the [[Cretaceous]]."<ref name="dingus2010" /> [[Henry Fairfield Osborn]], president of the [[American Museum of Natural History]], named the second skeleton ''T. rex'' in 1905. The generic name is derived from the [[Greek language|Greek]] words {{lang|grc|τύραννος}} ({{translit|grc|tyrannos}}, meaning "tyrant") and {{lang|grc|[[wikt:σαῦρος|σαῦρος]]}} ({{translit|grc|sauros}}, meaning "lizard"). Osborn used the [[Latin language|Latin]] word {{lang|la|rex}}, meaning "king", for the specific name. The full [[Binomial nomenclature|binomial]] therefore translates to "tyrant lizard the king" or "King Tyrant Lizard", emphasizing the animal's size and presumed dominance over other species of the time.<ref name="osborn1905" />

[[File:Dynamosaurus holotype.jpg|thumb|left|''Dynamosaurus imperiosus'' [[holotype]] (NHMUK PV R8020, previously AMNH 5886) on display at the [[Natural History Museum, London|Natural History Museum]], London]]
Osborn named the other specimen ''Dynamosaurus imperiosus'' in a paper in 1905.<ref name="osborn1905" /> In 1906, Osborn recognized that the two skeletons were from the same species and selected ''Tyrannosaurus'' as the preferred name.<ref name="osborn1906" /> In 1941, the ''T. rex'' type specimen was sold to the [[Carnegie Museum of Natural History]] in Pittsburgh, Pennsylvania, for $7,000.<ref name="dingus2010">{{Cite book |title=Barnum Brown: The Man Who Discovered ''Tyrannosaurus rex'' |url=https://archive.org/details/barnumbrownmanwh00ding |url-access=limited |last1=Dingus |first1=L. |last2=Norell |first2=M. |date=May 3, 2010 |publisher=University of California Press |isbn=978-0-520-94552-4 |pages=[https://archive.org/details/barnumbrownmanwh00ding/page/n106 90], 124}}</ref> The original ''Dynamosaurus'' material now resides in the collections of the [[Natural History Museum, London|Natural History Museum]], London.<ref name="Breithaupt">{{Cite journal |last1=Breithaupt |first1=B. H. |last2=Southwell |first2=E. H. |last3=Matthews |first3=N. A. |date=2006 |editor-last=Lucas |editor-first=S. G. |editor2-last=Sullivan |editor2-first=R. M. |title=''Dynamosaurus imperiosus'' and the earliest discoveries of ''Tyrannosaurus rex'' in Wyoming and the West |url=http://econtent.unm.edu/utils/getdownloaditem/collection/bulletins/id/693/filename/694.pdf/mapsto/pdf |format=PDF |journal=New Mexico Museum of Natural History and Science Bulletin |volume=35 |page=258 |quote=The original skeleton of ''Dynamosaurus imperiosus'' (AMNH 5866/BM R7995), together with other ''T. rex'' material (including parts of AMNH 973, 5027, and 5881), were sold to the British Museum of Natural History (now The Natural History Museum) in 1960. This material was used in an interesting 'half-mount' display of this dinosaur in London. Currently the material resides in the research collections. |archive-date=August 1, 2019 |access-date=June 25, 2015 |archive-url=https://web.archive.org/web/20190801022355/http://econtent.unm.edu/utils/getdownloaditem/collection/bulletins/id/693/filename/694.pdf/mapsto/pdf |url-status=live }}</ref> ''Dynamosaurus'' would later be honored by the 2018 description of another species of tyrannosaurid by Andrew McDonald and colleagues, ''[[Dynamoterror dynastes]]'', whose name was chosen in reference to the 1905 name, as it had been a "childhood favorite" of McDonald's.<ref name="McDonald2018">{{Cite journal |last1=McDonald |first1=A. T. |last2=Wolfe |first2=D. G. |last3=Dooley |first3=A. C. Jr. |date=2018 |title=A new tyrannosaurid (Dinosauria: Theropoda) from the Upper Cretaceous Menefee Formation of New Mexico |journal=PeerJ |volume=6 |page=6:e5749 |article-number=e5749 |doi=10.7717/peerj.5749 |pmid=30324024|pmc=6183510 |doi-access=free  |issn = 2167-8359}}</ref>

From the 1910s through the end of the 1950s, Barnum's discoveries remained the only specimens of ''Tyrannosaurus'', as the [[Great Depression]] and wars kept many paleontologists out of the field.<ref name="larson2008" />

===Continued study===
[[File:FMNH SUE Trex.jpg|alt=|thumb|Specimen "[[Sue (dinosaur)|Sue]]", [[Field Museum of Natural History]], Chicago]]
Beginning in the 1960s, there was renewed interest in ''Tyrannosaurus'', resulting in the recovery of 42 skeletons (5–80% complete by bone count) from Western North America.<ref name="larson2008" /> In 1967, Dr. William MacMannis located and recovered the skeleton named "MOR 008", which is 15% complete by bone count and has a reconstructed skull displayed at the [[Museum of the Rockies]]. The 1990s saw numerous discoveries, with nearly twice as many finds as in all previous years, including two of the most complete skeletons found to date: [[Sue (dinosaur)|Sue]] and [[Stan (dinosaur)|Stan]].<ref name="larson2008" />

[[Sue Hendrickson]], an [[amateur]] paleontologist, discovered the most complete (approximately 85%) and largest ''Tyrannosaurus'' skeleton in the [[Hell Creek Formation]] on August 12, 1990. The specimen Sue, named after the discoverer, was the object of a legal battle over its ownership. In 1997, the litigation was settled in favor of Maurice Williams, the original land owner. The fossil collection was purchased by the [[Field Museum of Natural History]] at auction for $7.6&nbsp;million, making it the most expensive dinosaur skeleton until the sale of Stan for $31.8 million in 2020.<ref>{{cite news |title=T. Rex Skeleton Brings $31.8 Million at Christie's Auction |url=https://www.nytimes.com/2020/10/06/arts/design/t-rex-skeleton-brings-31-8-million-at-christies-auction.html |archive-url=https://web.archive.org/web/20201007175400/https://www.nytimes.com/2020/10/06/arts/design/t-rex-skeleton-brings-31-8-million-at-christies-auction.html |archive-date=October 7, 2020 |url-access=subscription |url-status=live |website=The New York Times |date=October 7, 2020 |access-date=May 5, 2021|last1=Small |first1=Zachary }}</ref> From 1998 to 1999, Field Museum of Natural History staff spent over 25,000 hours taking the rock off the bones.<ref name="Sueprep">{{Cite web |url=http://archive.fieldmuseum.org/sue/?_ga=1.256723145.352611903.1414146341#preparing |title=Preparing Sue's bones |year=2007 |website=Sue at the Field Museum |publisher=The Field Museum |access-date=October 24, 2014 |archive-date=January 1, 2016 |archive-url=https://web.archive.org/web/20160101183701/http://archive.fieldmuseum.org/sue/?_ga=1.256723145.352611903.1414146341#preparing |url-status=live }}</ref> The bones were then shipped to [[New Jersey]] where the mount was constructed, then shipped back to Chicago for the final assembly. The mounted skeleton opened to the public on May 17, 2000, in the Field Museum of Natural History. A study of this specimen's fossilized bones showed that Sue reached full size at age 19 and died at the age of 28, the longest estimated life of any tyrannosaur known.<ref name="Ericksonetal2004TyrannosaurGigantism">{{Cite journal |last1=Erickson |first1=G. |last2=Makovicky |first2=P. J. |last3=Currie |first3=P. J. |last4=Norell |first4=M. |last5=Yerby |first5=S. |last6=Brochu |first6=C. A. |s2cid=4404887 |date=May 26, 2004 |title=Gigantism and life history parameters of tyrannosaurid dinosaurs |journal=Nature |volume=430 |issue=7001 |pages=772–775 |bibcode=2004Natur.430..772E |doi=10.1038/nature02699 |pmid=15306807 |url=http://doc.rero.ch/record/15279/files/PAL_E2578.pdf |archive-date=July 14, 2020 |access-date=November 23, 2022 |archive-url=https://web.archive.org/web/20200714024211/http://doc.rero.ch/record/15279/files/PAL_E2578.pdf |url-status=live }}{{Erratum|doi=10.1038/nature16487|pmid=26675726|http://retractionwatch.com/2016/03/01/high-profile-critic-slams-nature-letters-about-dinosaur-growth-following-corrections/ ''Retraction Watch''}}</ref> 
[[File:Scotty Tyrannosaurus.jpg|thumb|left|"[[Scotty (dinosaur)|Scotty]]", the largest known specimen, exhibited in Japan]]
Another ''Tyrannosaurus'', nicknamed Stan (BHI 3033), in honor of amateur paleontologist Stan Sacrison, was recovered from the Hell Creek Formation in 1992. Stan is the second most complete skeleton found, with 199 bones recovered representing 70% of the total.<ref>{{Cite web |url=http://www.museum.manchester.ac.uk/yourvisit/galleries/stan/ |title=Stan |date=September 18, 2010 |website=The University of Manchester |archive-url=https://web.archive.org/web/20100918104233/http://www.museum.manchester.ac.uk/yourvisit/galleries/stan/ |archive-date=September 18, 2010 }}</ref> This tyrannosaur also had many bone pathologies, including broken and healed ribs, a broken (and healed) neck, and a substantial hole in the back of its head, about the size of a ''Tyrannosaurus'' tooth.<ref>{{Cite book |title=''Tyrannosaurus'' Sue |url=https://archive.org/details/tyrannosaurussue00fiff_672 |url-access=limited |last=Fiffer |first=S. |publisher=W. H. Freeman and Company, New York |year=2000 |isbn=978-0-7167-4017-9 |pages=[https://archive.org/details/tyrannosaurussue00fiff_672/page/n139 121]–122 |chapter=Jurassic Farce}}</ref>

In 1998, 20-year-old Bucky Derflinger noticed a ''T. rex'' toe exposed above ground, making him the youngest person to discover a ''Tyrannosaurus''. The specimen, dubbed [[Specimens of Tyrannosaurus#"Bucky": TCM 2001.90.1|Bucky]] in honor of its discoverer, was a young adult, {{convert|10|ft|m|order=flip}} tall and {{convert|35|ft|m|order=flip}} long. Bucky is the first ''Tyrannosaurus'' to be found that preserved a [[furcula]] (wishbone). Bucky is permanently displayed at [[The Children's Museum of Indianapolis]].<ref>{{cite web|url=https://www.childrensmuseum.org/blog/meet-bucky-the-teenage-t-rex-v2 |date=July 7, 2014 |title=Meet Bucky The Teenage T. Rex |work=[[The Children's Museum of Indianapolis|Children's Museum of Indianapolis]] |access-date=December 2, 2019 |url-status=live |archive-url=https://web.archive.org/web/20141227210245/http://www.childrensmuseum.org/blog/meet-bucky-the-teenage-t-rex-v2 |archive-date=December 27, 2014}}</ref>
[[File:Tyrannosaurus specimens.svg|thumb|The specimens "Sue", AMNH 5027, "Stan", and "Jane", to scale with a human.]]
In the summer of 2000, crews organized by [[Jack Horner (paleontologist)|Jack Horner]] discovered five ''Tyrannosaurus'' skeletons near the [[Fort Peck Reservoir]].<ref name="bbc-horner">{{cite news |url=http://news.bbc.co.uk/2/hi/science/nature/965609.stm |title=Dig pulls up five T. rex specimens |date=October 10, 2000 |access-date=December 13, 2008 |work=BBC News |archive-date=August 19, 2018 |archive-url=https://web.archive.org/web/20180819045859/http://news.bbc.co.uk/2/hi/science/nature/965609.stm |url-status=live }}</ref> In 2001, a 50% complete skeleton of a juvenile ''Tyrannosaurus'' was discovered in the Hell Creek Formation by a crew from the [[Burpee Museum of Natural History]]. Dubbed Jane (BMRP 2002.4.1), the find was thought to be the first known skeleton of a [[pygmy]] tyrannosaurid, ''[[Nanotyrannus]]'', but other researchers considered it as the most complete juvenile ''T. rex'';<ref name="currieetal2003">{{Cite journal |last1=Currie |first1=P. J. |last2=Hurum |first2=J. H. |last3=Sabath |first3=K. |date=2003 |title=Skull structure and evolution in tyrannosaurid dinosaurs |url=http://www.app.pan.pl/archive/published/app48/app48-227.pdf |journal=Acta Palaeontologica Polonica |volume=48 |issue=2 |pages=227–234 |access-date=October 8, 2008 |archive-date=October 31, 2008 |archive-url=https://web.archive.org/web/20081031093118/http://www.app.pan.pl/archive/published/app48/app48-227.pdf |url-status=live }}</ref> currently exhibited at the Burpee Museum of Natural History, Jane is now re-described as the holotype of ''N. lethaeus''.<ref name="Z&N25"/> In 2002, a skeleton nicknamed "Wyrex", discovered by amateur collectors Dan Wells and Don Wyrick, had 114 bones and was 38% complete. The dig was concluded over 3 weeks in 2004 by the [[Black Hills Institute]] with the first live [[online]] ''Tyrannosaurus'' excavation providing daily reports, photos, and video.<ref name="larson2008" />

In 2006, [[Montana State University]] revealed that it possessed the largest ''Tyrannosaurus'' skull yet discovered (from a specimen named MOR 008), measuring {{convert|5|ft|cm|0|sp=us}} long.<ref name =MOR008>{{Cite web |url=http://www.montana.edu/cpa/news/nwview.php?article=3607 |title=Museum unveils world's largest ''T-rex'' skull. |work=Montana State University |date=2006 |archive-url=https://web.archive.org/web/20060414021235/http://www.montana.edu/cpa/news/nwview.php?article=3607 |archive-date=April 14, 2006 |access-date=April 7, 2006}}</ref> Subsequent comparisons indicated that the longest head was {{convert|136.5|cm|in}} (from specimen LACM 23844) and the widest head was {{convert|90.2|cm|in}} (from Sue).<ref name="gignac">{{Cite journal |last1=Gignac |first1=P. M. |last2=Erickson |first2=G. M. |year=2017 |title=The biomechanics behind extreme osteophagy in ''Tyrannosaurus rex'' |journal=Scientific Reports |volume=7 |issue=1 |page=2012 |bibcode=2017NatSR...7.2012G |doi=10.1038/s41598-017-02161-w |pmc=5435714 |pmid=28515439}}</ref>

==Description==
===Size===
[[File:Longest theropods.svg|alt=|thumb|350x350px|Size (in blue) compared to select giant theropods and a human]]
''T. rex'' was one of the largest land carnivores of all time. One of its largest and the most complete specimens, nicknamed [[Sue (dinosaur)|Sue]] (FMNH PR2081), is located at the [[Field Museum of Natural History]] in Chicago. Sue measured {{cvt|12.3|-|12.4|m}} long,<ref name="Hutchinsonet.al.2011">{{Cite journal |last1=Hutchinson |first1=J. R. |last2=Bates |first2=K. T. |last3=Molnar |first3=J. |last4=Allen |first4=V. |last5=Makovicky |first5=P. J. |date=2011 |title=A Computational Analysis of Limb and Body Dimensions in Tyrannosaurus rex with Implications for Locomotion, Ontogeny, and Growth |journal=PLOS ONE |volume=6 |issue=10 |article-number=e26037 |bibcode=2011PLoSO...626037H |doi=10.1371/journal.pone.0026037 |pmc=3192160 |pmid=22022500|doi-access=free }}</ref><ref name="Holtz2008">{{cite web|last1=Holtz|first1=T. R.|title=Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix|url=http://www.geol.umd.edu/~tholtz/dinoappendix/HoltzappendixWinter2011.pdf|access-date=January 13, 2012|date=2011|archive-date=August 12, 2017|archive-url=https://web.archive.org/web/20170812011954/http://www.geol.umd.edu/~tholtz/dinoappendix/HoltzappendixWinter2011.pdf|url-status=live}}</ref> was {{cvt|3.66|-|3.96|m}} tall at the hips,<ref name="SueFMNH">{{Cite web |url=https://www.fieldmuseum.org/sites/default/files/Sue%20Fact%20Sheet.pdf |title=Sue Fact Sheet |website=Sue at the Field Museum |publisher=[[Field Museum of Natural History]] |archive-url=https://web.archive.org/web/20160818213556/https://www.fieldmuseum.org/sites/default/files/Sue%20Fact%20Sheet.pdf |archive-date=August 18, 2016 }}</ref><ref name=Sue>{{cite web |author=<!--none given--> |title=How well do you know SUE? |date=August 11, 2016 |publisher=Field Museum of Natural History |url=https://www.fieldmuseum.org/blog/how-well-do-you-know-sue |access-date=December 31, 2018 |archive-date=April 8, 2022 |archive-url=https://web.archive.org/web/20220408042134/https://www.fieldmuseum.org/blog/how-well-do-you-know-sue |url-status=live }}</ref><ref name="FMNH">{{Cite web |date=February 5, 2018 |url=https://www.fieldmuseum.org/blog/sue-t-rex |title=Sue the T. Rex |website=Field Museum |access-date=July 20, 2018 |archive-date=April 4, 2014 |archive-url=https://web.archive.org/web/20140404170459/http://fieldmuseum.org/sue |url-status=live }}</ref> and according to the most recent studies, using a variety of techniques, maximum body masses have been estimated approximately {{cvt|8.4|-|9.22|MT}}.<ref name="Persons"/><ref name="HartmanMassEstimate">{{cite web |last=Hartman |first=Scott |date=July 7, 2013 |title=Mass estimates: North vs South redux |publisher=Scott Hartman's Skeletal Drawing.com |url=http://www.skeletaldrawing.com/home/mass-estimates-north-vs-south-redux772013 |access-date=August 24, 2013 |archive-date=October 12, 2013 |archive-url=https://web.archive.org/web/20131012065922/http://www.skeletaldrawing.com/home/mass-estimates-north-vs-south-redux772013 |url-status=live }}</ref><ref name="nicolas2014">{{Cite journal |last1=Campione |first1=Nicolás E. |last2=Evans |first2=David C. |last3=Brown |first3=Caleb M. |last4=Carrano |first4=Matthew T. |year=2014 |title=Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions |journal=Methods in Ecology and Evolution |volume=5 |issue=9 |pages=913–923 |doi=10.1111/2041-210X.12226 |s2cid=84317234|doi-access=free |bibcode=2014MEcEv...5..913C }}</ref> A specimen nicknamed [[Scotty (dinosaur)|Scotty]] (RSM P2523.8), located at the [[Royal Saskatchewan Museum]], is reported to measure {{cvt|13|m|ft}} in length. Using a mass estimation technique that extrapolates from the [[circumference]] of the femur, Scotty was estimated as the largest known specimen at {{cvt|8.87|MT}} in body mass.<ref name="Persons">{{Cite journal |last1=Persons |first1=S. W. |last2=Currie |first2=P. J. |last3=Erickson |first3=G. M. |title=An Older and Exceptionally Large Adult Specimen of ''Tyrannosaurus rex'' |journal=The Anatomical Record |volume=303 |issue=4 |pages=656–672 |doi=10.1002/ar.24118 |pmid=30897281 |issn=1932-8486|year=2019 |doi-access=free }}</ref><ref name="Lyle2019">{{Cite web |url=https://www.folio.ca/paleontologists-identify-biggest-tyrannosaurus-rex-ever-discovered/ |title=Paleontologists identify biggest ''Tyrannosaurus rex'' ever discovered |last=Lyle |first=A. |date=March 22, 2019 |publisher=Folio, University of Alberta |access-date=March 25, 2019 |archive-date=August 4, 2020 |archive-url=https://web.archive.org/web/20200804134550/https://www.folio.ca/paleontologists-identify-biggest-tyrannosaurus-rex-ever-discovered/ |url-status=live }}</ref>

Not every adult ''Tyrannosaurus'' specimen recovered is as big. Historically average adult mass estimates have varied widely over the years, from as low as {{cvt|4.5|MT}},<ref name="andersonetal1985">{{Cite journal |last1=Anderson |first1=J. F. |last2=Hall-Martin |first2=A. J. |last3=Russell |first3=D. |author-link3=Dale Russell |date=1985 |title=Long bone circumference and weight in mammals, birds and dinosaurs |journal=Journal of Zoology |volume=207 |issue=1 |pages=53–61  |doi=10.1111/j.1469-7998.1985.tb04915.x}}</ref><ref name="bakker1986">{{Cite book |title=The Dinosaur Heresies |last=Bakker |first=R. T. |date=1986 |publisher=Kensington Publishing |isbn=978-0-688-04287-5 |location=New York |page=[https://archive.org/details/dinosaurheresies00robe/page/241 241] |oclc=13699558 |author-link=Robert T. Bakker |url=https://archive.org/details/dinosaurheresies00robe/page/241 }}</ref> to more than {{cvt|7.2|MT}},<ref name="henderson1999">{{Cite journal |last=Henderson |first=D. M. |date=January 1, 1999 |title=Estimating the masses and centers of mass of extinct animals by 3-D mathematical slicing |url=http://paleobiol.geoscienceworld.org/cgi/content/abstract/25/1/88 |journal=Paleobiology |volume=25 |issue=1 |pages=88–106 |archive-date=July 26, 2011 |access-date=December 23, 2007 |archive-url=https://web.archive.org/web/20110726105529/http://paleobiol.geoscienceworld.org/cgi/content/abstract/25/1/88 |url-status=live }}</ref> with most modern estimates ranging between {{cvt|5.4|and|8.0|MT}}.<ref name="Hutchinsonet.al.2011" /><ref name="ericksonetal2004">{{Cite journal |last1=Erickson |first1=G. M. |last2=Makovicky |first2=P. J. |last3=Currie |first3=P. J. |author-link3=Phil Currie |last4=Norell |first4=M. A. |last5=Yerby |first5=S. A. |last6=Brochu |first6=C. A. |s2cid=4404887 |date=2004 |title=Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs |journal=Nature |volume=430 |issue=7001 |pages=772–775 |bibcode=2004Natur.430..772E |doi=10.1038/nature02699 |pmid=15306807 |url=http://doc.rero.ch/record/15279/files/PAL_E2578.pdf |archive-date=July 14, 2020 |access-date=November 23, 2022 |archive-url=https://web.archive.org/web/20200714024211/http://doc.rero.ch/record/15279/files/PAL_E2578.pdf |url-status=live }}{{Erratum|doi=10.1038/nature16487|pmid=26675726|http://retractionwatch.com/2016/03/01/high-profile-critic-slams-nature-letters-about-dinosaur-growth-following-corrections/ ''Retraction Watch''}}</ref><ref name="farlowetal1995">{{Cite journal |last1=Farlow |first1=J. O. |last2=Smith |first2=M. B. |last3=Robinson |first3=J. M. |date=1995 |title=Body mass, bone 'strength indicator', and cursorial potential of ''Tyrannosaurus rex'' |url=http://www.vertpaleo.org/publications/jvp/15-713-725.cfm  |journal=Journal of Vertebrate Paleontology |volume=15 |issue=4 |pages=713–725 |doi=10.1080/02724634.1995.10011257 |bibcode=1995JVPal..15..713F |archive-url=https://web.archive.org/web/20081023063102/http://www.vertpaleo.org/publications/jvp/15-713-725.cfm |archive-date=October 23, 2008|url-access=subscription }}</ref><ref name="seebacher2001">{{Cite journal |last=Seebacher |first=F. |date=2001 |title=A new method to calculate allometric length–mass relationships of dinosaurs |url=http://dinoweb.ucoz.ru/_fr/4/A_new_method_to.pdf |journal=Journal of Vertebrate Paleontology |volume=21 |issue=1 |pages=51–60 |citeseerx=10.1.1.462.255 |doi=10.1671/0272-4634(2001)021[0051:ANMTCA]2.0.CO;2 |s2cid=53446536 |archive-date=March 4, 2016 |access-date=August 6, 2018 |archive-url=https://web.archive.org/web/20160304002456/http://dinoweb.ucoz.ru/_fr/4/A_new_method_to.pdf |url-status=live }}</ref><ref name="christiansenfarina2004">{{Cite journal |last1=Christiansen |first1=P. |last2=Fariña |first2=R. A. |s2cid=84322349 |date=2004 |title=Mass prediction in theropod dinosaurs |journal=Historical Biology |volume=16 |issue=2–4 |pages=85–92 |doi=10.1080/08912960412331284313|bibcode=2004HBio...16...85C }}</ref>

A 2024 study found that there was little evidence of size-based sexual dimorphism in ''T. rex''.<ref name="Mallon&Hone24">{{Cite journal |last1=Mallon |first1=Jordan C. |last2=Hone |first2=David W. E. |date=July 24, 2024 |title=Estimation of maximum body size in fossil species: A case study using ''Tyrannosaurus rex'' |journal=[[Ecology and Evolution]] |language=en |volume=14 |issue=7 |article-number=11658 |doi=10.1002/ece3.11658 |issn=2045-7758 |pmc=11267449 |pmid=39050661|bibcode=2024EcoEv..1411658M }}</ref>

===Skull===
[[File:Tyrannosaurus rex AMNH 5027 skull.png|thumb|Skull of specimen AMNH 5027 with labelled diagrams in dorsal, lateral, anterior, posterior, and medial (lower jaw) views]]
The largest known ''T. rex'' skulls measure up to {{cvt|1.52|m|ftin}} in length.<ref name="MOR008" /><ref name="SueFMNH" /> Large [[Fenestra (anatomy)|fenestrae]] (openings) in the skull reduced weight, as in all carnivorous theropods. In other respects ''Tyrannosaurus''<nowiki>'</nowiki>s skull was significantly different from those of large non-[[tyrannosaurid]] theropods. It was extremely wide at the rear but had a narrow snout, allowing unusually good [[binocular vision]].<ref name="Stevens2006Binocular">{{Cite journal|last=Stevens |first=Kent A. |date=June 2006 |title=Binocular vision in theropod dinosaurs |journal=Journal of Vertebrate Paleontology |issue=2 |pages=321–330 |volume=26 |doi=10.1671/0272-4634(2006)26[321:BVITD]2.0.CO;2|s2cid=85694979 }}</ref><ref name="jaffe">{{Cite journal |last=Jaffe |first=E. |date=July 1, 2006 |title=Sight for 'Saur Eyes: ''T. rex'' vision was among nature's best |url=http://www.sciencenews.org/view/generic/id/7500/title/Sight_for_Saur_Eyes_%3Ci%3ET._rex%3Ci%3E_vision_was_among_natures_best |journal=[[Science News]] |volume=170 |issue=1 |pages=3–4 |doi=10.2307/4017288 |jstor=4017288 |access-date=October 6, 2008 |archive-date=September 29, 2012 |archive-url=https://web.archive.org/web/20120929190336/http://www.sciencenews.org/view/generic/id/7500/title/Sight_for_Saur_Eyes_%3Ci%3ET._rex%3Ci%3E_vision_was_among_natures_best  |url-access=subscription }}</ref> The skull bones were massive and the [[nasal bone|nasals]] and some other bones were fused, preventing movement between them; but many were [[Pneumatized bones|pneumatized]] (contained a "honeycomb" of tiny air spaces) and thus lighter. These and other skull-strengthening features are part of the [[tyrannosaurid]] trend towards an increasingly powerful bite, which easily surpassed that of all non-tyrannosaurids.<ref name="SnivelyHendersonPhillips2006FusedVaultedNasals">{{Cite journal |last1=Snively |first1=E. |last2=Henderson |first2=D. M. |last3=Phillips |first3=D. S. |year=2006 |title=Fused and vaulted nasals of tyrannosaurid dinosaurs: Implications for cranial strength and feeding mechanics |url=http://www.app.pan.pl/archive/published/app51/app51-435.pdf |journal=Acta Palaeontologica Polonica |volume=51 |issue=3 |pages=435–454 |access-date=October 8, 2008 |archive-date=August 19, 2018 |archive-url=https://web.archive.org/web/20180819045612/http://www.app.pan.pl/archive/published/app51/app51-435.pdf |url-status=live }}</ref><ref name="MM03">{{Cite journal |last=Meers |first=M. B. |s2cid=86782853 |date=August 2003 |title=Maximum bite force and prey size of ''Tyrannosaurus rex'' and their relationships to the inference of feeding behavior |journal=Historical Biology |volume=16 |issue=1 |pages=1–12 |doi=10.1080/0891296021000050755}}</ref><ref name="GEetal96">{{Cite journal |last1=Erickson |first1=G. M. |last2=Van Kirk |first2=S. D. |last3=Su |first3=J. |last4=Levenston |first4=M. E. |last5=Caler |first5=W. E. |last6=Carter |first6=D. R. |s2cid=4325859 |year=1996 |title=Bite-force estimation for ''Tyrannosaurus rex'' from tooth-marked bones |journal=Nature |volume=382 |issue=6593 |pages=706–708 |bibcode=1996Natur.382..706E |doi=10.1038/382706a0 |url=https://zenodo.org/record/3730962 |archive-date=July 4, 2020 |access-date=July 4, 2020 |archive-url=https://web.archive.org/web/20200704181008/https://zenodo.org/record/3730962 |url-status=live }}</ref> The tip of the upper jaw was U-shaped (most non-tyrannosauroid carnivores had V-shaped upper jaws), which increased the amount of tissue and bone a tyrannosaur could rip out with one bite, although it also increased the stresses on the front teeth.<ref name="holtz1994" />

The teeth of ''T. rex'' displayed marked [[heterodont]]y (differences in shape).<ref name="brochu2003">{{Cite journal |last=Brochu |first=C. R. |year=2003 |title=Osteology of ''Tyrannosaurus rex'': insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull |journal=Society of Vertebrate Paleontology Memoirs |volume=7 |pages=1–138 |doi=10.2307/3889334 |jstor=3889334 |url=http://publication.plazi.org/id/6603FFA80B5D0D64FFF6AB533D39FF9A |archive-date=March 24, 2025 |access-date=May 24, 2025 |archive-url=https://web.archive.org/web/20250324135253/http://publication.plazi.org/id/6603FFA80B5D0D64FFF6AB533D39FF9A |url-status=live }}</ref><ref name="Smith2005HeterodontyTRex">{{Cite journal |last=Smith |first=J. B. |date=December 1, 2005 |title=Heterodonty in ''Tyrannosaurus rex'': implications for the taxonomic and systematic utility of theropod dentitions |journal=Journal of Vertebrate Paleontology |volume=25 |issue=4 |pages=865–887 |doi=10.1671/0272-4634(2005)025[0865:HITRIF]2.0.CO;2 |s2cid=86184190 |url=http://publication.plazi.org/id/DC6AFFF0D024FFD5FFA3FFD8BE03D62F |archive-date=March 24, 2025 |access-date=May 24, 2025 |archive-url=https://web.archive.org/web/20250324034130/http://publication.plazi.org/id/DC6AFFF0D024FFD5FFA3FFD8BE03D62F |url-status=live }}</ref> The [[premaxilla]]ry teeth, four per side at the front of the upper jaw, were closely packed, ''D''-shaped in cross-section, had reinforcing ridges on the rear surface, were [[Incisor|incisiform]] (their tips were chisel-like blades) and curved backwards. The ''D''-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when ''Tyrannosaurus'' bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers, more widely spaced and also had reinforcing ridges.<ref name="New Scientist1998DinosaurDetectives">{{Cite magazine |last1=Douglas |first1=K. |last2=Young |first2=S. |year=1998 |title=The dinosaur detectives |url=https://www.newscientist.com/channel/life/dinosaurs/mg15821305.300 |magazine=[[New Scientist]] |access-date=October 16, 2008 |quote=One palaeontologist memorably described the huge, curved teeth of T. rex as 'lethal bananas' |archive-date=May 17, 2008 |archive-url=https://web.archive.org/web/20080517160559/http://www.newscientist.com/channel/life/dinosaurs/mg15821305.300 |url-status=live }}</ref> Those in the upper jaw, twelve per side in mature individuals,<ref name="brochu2003" /> were larger than their counterparts of the lower jaw, except at the rear. The largest found so far is estimated to have been {{cvt|30.5|cm}} long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found.<ref name="SueFMNH2">{{Cite web |url=http://www.fieldmuseum.org/sue/about_vital.asp |title=Sue's vital statistics |website=Sue at the Field Museum |publisher=[[Field Museum of Natural History]] |archive-url=https://web.archive.org/web/20070929090231/http://www.fieldmuseum.org/SUE/about_vital.asp <!--Added by H3llBot--> |archive-date=September 29, 2007 |access-date=September 15, 2007}}</ref> The lower jaw was robust. Its front [[dentary bone]] bore thirteen teeth. Behind the tooth row, the lower jaw became notably taller.<ref name="brochu2003" /> The upper and lower jaws of ''Tyrannosaurus'', like those of many dinosaurs, possessed numerous [[Foramen|foramina]], or small holes in the bone. Various functions have been proposed for these foramina, such as a crocodile-like sensory system<ref name="carr2017" /> or evidence of [[Integument|extra-oral structures]] such as scales or potentially lips,<ref>{{Cite thesis|last=Morhardt|first=Ashley|year=2009|title=Dinosaur smiles: Do the texture and morphology of the premaxilla, maxilla, and dentary bones of sauropsids provide osteological correlates for inferring extra-oral structures reliably in dinosaurs?|url=https://www.academia.edu/3871353|publisher=Western Illinois University|type=MSc thesis|archive-date=February 10, 2022|access-date=May 10, 2020|archive-url=https://web.archive.org/web/20220210063525/https://www.academia.edu/3871353|url-status=live}}</ref><ref name=":0" /><ref name="MontevialeCroc" /> with subsequent research on theropod tooth wear patterns supporting such a proposition.<ref name=CullenEtAl23>{{Cite journal |last1=Cullen |first1=Thomas M. |last2=Larson |first2=Derek W. |last3=Witton |first3=Mark P. |last4=Scott |first4=Diane |last5=Maho |first5=Tea |last6=Brink |first6=Kirstin S. |last7=Evans |first7=David C. |last8=Reisz |first8=Robert |date=March 31, 2023 |title=Theropod dinosaur facial reconstruction and the importance of soft tissues in paleobiology |journal=Science |language=en |volume=379 |issue=6639 |pages=1348–1352 |doi=10.1126/science.abo7877 |pmid=36996202 |bibcode=2023Sci...379.1348C |s2cid=257836765 |issn=0036-8075|doi-access=free }}</ref>

===Skeleton===
{{multiple image
| align             = left
| perrow            = 1
| total_width       = 250
| image1            = Tyrannosaurus-rex-Profile-steveoc86 (coloured)(mirror).png
| caption1          = [[Paleoart|Life restoration]] showing scaly skin with sparse feathering, and lipped jaws
| image2            = Tyrannosaurus Sue skeletal reconstruction.png
| caption2          = Skeletal reconstruction of specimen "Sue"
}}
The [[vertebral column]] of ''Tyrannosaurus'' consisted of ten neck vertebrae, thirteen back vertebrae and five sacral vertebrae. The number of tail vertebrae is unknown and could well have varied between individuals but probably numbered at least forty. Sue was mounted with forty-seven of such caudal vertebrae.<ref name="brochu2003" /> The neck of ''T. rex'' formed a natural S-shaped curve like that of other theropods. Compared to these, it was exceptionally short, deep and muscular to support the massive head. The second vertebra, the axis, was especially short. The remaining neck vertebrae were weakly opisthocoelous, i.e. with a convex front of the vertebral body and a concave rear. The vertebral bodies had single pleurocoels, pneumatic depressions created by [[air sac]]s, on their sides.<ref name="brochu2003" /> The vertebral bodies of the torso were robust but with a narrow waist. Their undersides were keeled. The front sides were concave with a deep vertical trough. They had large pleurocoels. Their neural spines had very rough front and rear sides for the attachment of strong tendons. The sacral vertebrae were fused to each other, both in their vertebral bodies and neural spines. They were pneumatized. They were connected to the pelvis by transverse processes and sacral ribs. The tail was heavy and moderately long, in order to balance the massive head and torso and to provide space for massive [[Animal locomotion|locomotor muscles]] that attached to the thighbones. The thirteenth tail vertebra formed the transition point between the deep tail base and the middle tail that was stiffened by a rather long front articulation processes. The underside of the trunk was covered by eighteen or nineteen pairs of segmented belly ribs.<ref name="brochu2003" />
[[File:The Right Arm of SUE.jpg|thumb|Right forelimb of specimen "Sue"]]
The [[shoulder girdle]] was longer than the entire forelimb. The shoulder blade had a narrow shaft but was exceptionally expanded at its upper end. It connected via a long forward protrusion to the [[coracoid]], which was rounded. Both shoulder blades were connected by a small [[furcula]]. The paired breast bones possibly were made of [[cartilage]] only.<ref name="brochu2003" />

The forelimb or arm was very short. The upper arm bone, the humerus, was short but robust. It had a narrow upper end with an exceptionally rounded head. The lower arm bones, the [[ulna]] and radius, were straight elements, much shorter than the humerus. The second [[metacarpus|metacarpal]] was longer and wider than the first, whereas normally in theropods the opposite is true. The forelimbs had only two clawed fingers,<ref name="brochu2003" /> along with an additional splint-like small third [[metacarpus|metacarpal]] representing the remnant of a third digit.<ref name="CLKC08">{{Cite book |title=''Tyrannosaurus rex'', the Tyrant King |url=https://archive.org/details/tyrannosaurusrex00plar |url-access=limited |last1=Lipkin |first1=C. |last2=Carpenter |first2=K. |date=2008 |publisher=Indiana University Press |isbn=978-0-253-35087-9 |editor-last=Carpenter |editor-first=K. |location=Bloomington |pages=[https://archive.org/details/tyrannosaurusrex00plar/page/n182 167]–190 |chapter=Looking again at the forelimb of ''Tyrannosaurus rex'' |editor-last2=Larson |editor-first2=P. E.}}</ref>
[[File:UCMP Trex pelvis 2.JPG|thumb|left|Pelvic girdle of specimen MOR 555]]
The [[pelvis]] was a large structure. Its upper bone, the [[Ilium (bone)|ilium]], was both very long and high, providing an extensive attachment area for hindlimb muscles. The front [[pubic bone]] ended in an enormous pubic boot, longer than the entire shaft of the element. The rear [[ischium]] was slender and straight, pointing obliquely to behind and below.<ref name="brochu2003" />

In contrast to the arms, the hindlimbs were among the longest in proportion to body size of any theropod. In the foot, the [[metatarsus]] was "arctometatarsalian", meaning that the part of the third metatarsal near the ankle was pinched. The third metatarsal was also exceptionally sinuous.<ref name="brochu2003" /> Compensating for the immense bulk of the animal, many bones throughout the skeleton were hollowed, reducing its weight without significant loss of strength.<ref name="brochu2003" />

==Classification==
[[File:Tyrannosaurus skulls Japan.jpg|thumb|Skull casts of different ''Tyrannosaurus'' specimens]]
''Tyrannosaurus'' is the [[Type (biology)|type]] genus of the superfamily [[Tyrannosauroidea]], the [[Family (biology)|family]] [[Tyrannosauridae]], and the subfamily Tyrannosaurinae; in other words it is the standard by which paleontologists decide whether to include other species in the same group. Other members of the tyrannosaurine subfamily include the North American ''[[Daspletosaurus]]'' and the [[Asia]]n ''[[Tarbosaurus]]'',<ref name="currieetal2003" /><ref name="holtz2004">{{Cite book |title=The dinosauria |url=https://archive.org/details/dinosauriandedit00weis |url-access=limited |last=Holtz | first=T. R. Jr. |date=2004 |publisher=University of California Press |isbn=978-0-520-24209-8 |editor-last=Weishampel |editor-first=D. B. |editor-link=David B. Weishampel |location=Berkeley |pages=[https://archive.org/details/dinosauriandedit00weis/page/n129 111]–136 |chapter=Tyrannosauroidea |author-link=Thomas R. Holtz Jr. |editor-last2=Dodson |editor-first2=P. |editor-link2=Peter Dodson |editor-last3=Osmólska |editor-first3=H. |editor-link3=Halszka Osmólska}}</ref> both of which have occasionally been synonymized with ''Tyrannosaurus''.<ref name="paul1988">{{cite book |last=Paul |first=Gregory S. |author-link=Gregory S. Paul |date=1988 |title=Predatory dinosaurs of the world: a complete illustrated guide |publisher=Simon and Schuster |location=New York |isbn=978-0-671-61946-6 |oclc=18350868 |page=[https://archive.org/details/predatorydinosau00paul/page/228 228] |url=https://archive.org/details/predatorydinosau00paul/page/228 }}</ref>

Tyrannosaurids were once commonly thought to be descendants of earlier large theropods such as [[Spinosauroidea|megalosaurs]] and [[Carnosauria|carnosaurs]], although more recently they were reclassified with the generally smaller [[Coelurosauria|coelurosaurs]].<ref name="holtz1994">{{Cite journal |last=Holtz |first=T. R. |author-link=Thomas R. Holtz Jr. |date=1994 |title=The Phylogenetic Position of the Tyrannosauridae: Implications for Theropod Systematics |journal=Journal of Paleontology |volume=68 |issue=5 |pages=1100–1117 |doi=10.1017/S0022336000026706 |jstor=1306180|bibcode=1994JPal...68.1100H |s2cid=129684676 }}</ref> The earliest tyrannosaur group were the crested proceratosaurids, while later and more derived members belong to the [[Pantyrannosauria]]. Tyrannosaurs started out as small theropods; however at least some became larger by the [[Early Cretaceous]].  It is quite likely that tyrannosauroids rose to prominence after the decline in allosauroid and megalosauroid diversity seen during the early stages of the Late Cretaceous.<ref>{{cite journal |title=A longirostrine tyrannosauroid from the Early Cretaceous of China |journal=Proc Biol Sci |date=2009 |volume=277 |issue=1679 |doi=10.1098/rspb.2009.0249 |pmc=2842666 |last1=Li |first1=Daqing |last2=Norell |first2=Mark A. |last3=Gao |first3=Ke-Qin |last4=Smith |first4=Nathan D. |last5=Makovicky |first5=Peter J. |pages=183–190 |pmid=19386654 }}</ref>

Tyrannosauroids are characterized by their fused nasals and dental arrangement. Pantyrannosaurs are characterized by unique features in their hips as well as an enlarged foramen in the quadrate, a broad postorbital and hourglass shaped nasals. Some of the more derived pantyrannosaurs lack nasal pneumaticity and have a lower humerus to femur ratio with their arms starting to see some reduction. Some pantyrannosaurs started developing an arctometatarsus. Eutyrannosaurs have a rough texture on their nasal bones and their mandibular fenestra is reduced externally. Tyrannosaurids lack kinetic skulls or special crests on their nasal bones, and have a lacrimal with a distinctive process on it. Tyrannosaurids also have an interfenestral strut that is less than half as big as the maxillary fenestra.<ref>{{Cite journal |last1=Brusatte |first1=Stephen L. |last2=Norell |first2=Mark A. |last3=Carr |first3=Thomas D. |last4=Erickson |first4=Gregory M. |last5=Hutchinson |first5=John R. |last6=Balanoff |first6=Amy M. |last7=Bever |first7=Gabe S. |last8=Choiniere |first8=Jonah N. |last9=Makovicky |first9=Peter J. |last10=Xu |first10=Xing |date=September 17, 2010 |title=Tyrannosaur Paleobiology: New Research on Ancient Exemplar Organisms |url=https://www.science.org/doi/10.1126/science.1193304 |journal=Science |language=en |volume=329 |issue=5998 |pages=1481–1485 |doi=10.1126/science.1193304 |pmid=20847260 |bibcode=2010Sci...329.1481B |issn=0036-8075 |archive-date=April 5, 2024 |access-date=April 5, 2024 |archive-url=https://web.archive.org/web/20240405184657/https://www.science.org/doi/10.1126/science.1193304 |url-status=live }}</ref>

Many [[phylogeny|phylogenetic]] analyses have found ''[[Tarbosaurus bataar]]'' to be the [[sister taxon]] of ''T. rex''.<ref name="holtz2004" /> The discovery of the tyrannosaurid ''[[Lythronax]]'' further indicates that ''Tarbosaurus'' and ''Tyrannosaurus'' are closely related, forming a clade with fellow Asian tyrannosaurid ''[[Zhuchengtyrannus]]'', with ''Lythronax'' being their sister taxon.<ref name="Loewen13" /><ref>{{cite magazine |url=https://news.nationalgeographic.com/news/2013/11/131106-king-gore-tyrannosaurus-dinosaur/ |archive-url=https://web.archive.org/web/20131108020332/http://news.nationalgeographic.com/news/2013/11/131106-king-gore-tyrannosaurus-dinosaur/ |archive-date=November 8, 2013 |title=Newfound "King of Gore" Dinosaur Ruled Before T. Rex |last=Vergano |first=D. |date=November 7, 2013 |magazine=National Geographic |access-date=November 10, 2017}}</ref> A further study from 2016 by Steve Brusatte, Thomas Carr and colleagues, also indicates that ''Tyrannosaurus'' may have been an immigrant from Asia, as well as a possible descendant of ''Tarbosaurus''.<ref>{{Cite web |url=http://www.livescience.com/53877-t-rex-was-invasive-species.html |title=''T. Rex'' Was Likely an Invasive Species |last=Geggel |first=L. |date=February 29, 2016 |website=Live Science |access-date=November 10, 2017 |archive-date=April 6, 2019 |archive-url=https://web.archive.org/web/20190406221051/https://www.livescience.com/53877-t-rex-was-invasive-species.html |url-status=live }}</ref>

Below is the cladogram of Tyrannosauridae based on the [[phylogenetic analysis]] conducted by Loewen and colleagues in 2013.<ref name="Loewen13">{{Cite journal |last1=Loewen |first1=M. A. |last2=Irmis |first2=R. B. |last3=Sertich |first3=J. J. W. |last4=Currie |first4=P. J. |author-link4=Philip J. Currie |last5=Sampson |first5=S. D. |author-link5=Scott D. Sampson |year=2013 |editor-last=Evans |editor-first=D. C |editor-link=David C. Evans (paleontologist) |title=Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans |journal=[[PLoS ONE]] |volume=8 |issue=11 |article-number=e79420 |bibcode=2013PLoSO...879420L |doi=10.1371/journal.pone.0079420 |pmc=3819173 |pmid=24223179 |ref={{sfnRef|Loewen et al.|2013}}|doi-access=free }}</ref>
{{clade| style=font-size:100%; line-height:100%
|label1=[[Tyrannosauridae]]
|1={{clade
   |label1=[[Albertosaurinae]]
   |1={{clade
      |1=''[[Gorgosaurus libratus]]'' [[File:Gorgosaurus flipped.png|70 px]]
      |2=''[[Albertosaurus sarcophagus]]'' <div style="{{MirrorH}}">[[File:Albertosaurus NT small.jpg|70px]]</div>}}
   |label2=[[Tyrannosaurinae]]
   |2={{clade
      |1=[[Dinosaur Park Formation|Dinosaur Park]] tyrannosaurid
      |2={{clade
         |1=''[[Daspletosaurus torosus]]'' [[File:Daspletosaurus torosus steveoc flipped.jpg|70 px]]
         |2={{clade
            |1=[[Two Medicine Formation|Two Medicine]] tyrannosaurid
            |2={{clade
               |1=''[[Teratophoneus curriei]]'' <div style="{{MirrorH}}">[[File:Teratophoneus curriei by PaleoGeek.png|70 px]]</div>
               |2={{clade
                  |1=''[[Bistahieversor sealeyi]]'' [[File:Bistahieversor sealeyi life restoration.jpg|70px]]
                  |2={{clade
                     |1=''[[Lythronax argestes]]'' [[File:Lythronax by Tomopteryx flipped.png|70 px]]
                     |2={{clade
                        |1='''''Tyrannosaurus rex''''' [[File:Tyrannosaurus-rex-Profile-steveoc86 (coloured).png|100 px]]
                        |2={{clade
                           |1=''[[Tarbosaurus bataar]]'' [[File:Tarbosaurus_Restorationadssasasdda.png|50 px]]
                           |2=''[[Zhuchengtyrannus magnus]]'' <div style="{{MirrorH}}">[[File:Zhuchengtyrannus magnus reconstruction.jpg|85px]]</div> 
}} }} }} }} }} }} }} }} }} }}

In their 2024 description of ''Tyrannosaurus mcraeensis'', Dalman et al. recovered similar results to previous analyses, with ''Tyrannosaurus'' as the sister taxon to the clade formed by ''Tarbosaurus'' and ''Zhuchengtyrannus'', called the Tyrannosaurini. They also found support for a [[monophyletic]] clade containing ''Daspletosaurus'' and ''[[Thanatotheristes]]'', typically referred to as the [[Daspletosaurini]].<ref name=T.mcraeensis/><ref name=SV24>{{Cite journal |last1=Scherer |first1=Charlie Roger |last2=Voiculescu-Holvad |first2=Christian |year=2024 |title=Re-analysis of a dataset refutes claims of anagenesis within ''Tyrannosaurus''-line tyrannosaurines (Theropoda, Tyrannosauridae) |journal=[[Cretaceous Research]] |volume=155 |article-number=105780 |doi=10.1016/j.cretres.2023.105780 |issn=0195-6671|doi-access=free |bibcode=2024CrRes.15505780S }}</ref>

{{clade
|{{clade
 |1={{clade
  |1=''[[Albertosaurus sarcophagus]]'' <div style="{{MirrorH}}">[[File:Albertosaurus NT small.jpg|70px]]</div>
  |2=''[[Gorgosaurus libratus]]'' [[File:Gorgosaurus flipped.png|70 px]]}}
  |3={{clade
  |1={{clade
  |1={{clade
 |1=''[[Daspletosaurus]] horneri''
 |2=''[[Thanatotheristes]]'' [[file:Thanatotheristes.jpg|70px]]}}
 |3={{clade
|1=''Daspletosaurus torosus'' [[File:Daspletosaurus torosus steveoc flipped.jpg|70 px]]
|2=''Daspletosaurus wilsoni'' }} }}
|3={{clade
|1=''[[Teratophoneus]]'' <div style="{{MirrorH}}">[[File:Teratophoneus curriei by PaleoGeek.png|70 px]]</div>
|2={{clade
 |1=''[[Nanuqsaurus]]'' [[File:Nanuqsaurus TD.png|70px]]
 |2={{clade
  |1=''[[Bistahieversor]]'' [[File:Bistahieversor sealeyi life restoration.jpg|70px]]
  |2={{clade
   |1=''[[Lythronax]]'' [[File:Lythronax by Tomopteryx flipped.png|70 px]]
   |label2=[[Tyrannosaurini]]
   |2={{clade
   |1={{clade
    |1='''''Tyrannosaurus mcraeensis''''' <div style="{{MirrorH}}">[[File:Tyrannosaurus mcraeensis.png|90 px]]</div>
    |2='''''Tyrannosaurus rex''''' [[File:Tyrannosaurus-rex-Profile-steveoc86 (coloured).png|100 px]] }}
    |3={{clade
   |1=''[[Zhuchengtyrannus]]'' <div style="{{MirrorH}}">[[File:Zhuchengtyrannus magnus reconstruction.jpg|85px]]</div>
   |2=''[[Tarbosaurus]]'' [[File:Tarbosaurus_Restorationadssasasdda.png|80 px]]
}} }} }} }} }} }} }} }} }}

===Additional species===
[[File:Tarbosaurus and Tyrannosaurus.jpg|thumb|Diagram showing the differences between a generalized ''Tarbosaurus'' (A) and ''Tyrannosaurus rex'' (B) skull]]
In 1955, Soviet [[paleontology|paleontologist]] [[Evgeny Maleev]] named a new species, ''Tyrannosaurus bataar'', from [[Mongolia]].<ref name="maleev1955">{{Cite journal |last=Maleev |first=E. A. |date=1955 |others=translated by F. J. Alcock |title=(title in Russian) |trans-title=Gigantic carnivorous dinosaurs of Mongolia |url=http://paleoglot.org/files/Maleev_55a.pdf |journal=[[Doklady Akademii Nauk SSSR]] |language=ru |volume=104 |issue=4 |pages=634–637 |archive-date=December 11, 2019 |access-date=April 30, 2013 |archive-url=https://web.archive.org/web/20191211124644/https://paleoglot.org/files/Maleev_55a.pdf |url-status=live }}</ref> By 1965, this species was renamed as a distinct genus, ''Tarbosaurus bataar''.<ref name="rozhdestvensky1965">{{Cite journal |last=Rozhdestvensky |first=A. K. |date=1965 |title=Growth changes in Asian dinosaurs and some problems of their taxonomy |journal=Paleontological Journal |volume=3 |pages=95–109}}</ref> While most paleontologists continue to maintain the two as distinct genera, some authors such as [[Thomas Holtz]], [[Kenneth Carpenter]], and [[Thomas Carr (paleontologist)|Thomas Carr]] argue that the two species are similar enough to be considered members of the same genus, restoring the Mongolian [[taxon]]'s original [[binomial nomenclature|binomial name]].<ref name=holtz1994/><ref name=carpenter1992>{{Cite book |title=Aspects of nonmarine Cretaceous geology |last=Carpenter |first=K. |date=1992 |publisher=China Ocean Press |isbn=978-7-5027-1463-5 |editor-last=Mateer |editor-first=N. J. |location=Beijing |pages=250–268 |chapter=Tyrannosaurids (Dinosauria) of Asia and North America |oclc=28260578 |author-link=Kenneth Carpenter |editor-last2=Chen |editor-first2=P.-j.}}</ref><ref name=carr2017/>

Some specimens from the Late Cretaceous deposits of [[China]] have been described as new species of ''Tyrannosaurus'': ''T.'' "lanpingensis" based on isolated [[lateral (anatomy)|lateral]] tooth from the red beds of [[Yunnan]] in 1975; ''T.'' "turpanensis" from the [[Subashi Formation]], [[Turpan Basin]], [[Xinjiang]] in 1978; and ''T. luanchuanensis'' from the [[Quiba Formation]], [[Tantou Basin]], [[Henan Province]] in 1979–1980.<ref>{{cite journal|author=Hurum, J.H., Sabath, K.|year=2003|url=https://www.app.pan.pl/archive/published/app48/app48-161.pdf|title=Giant theropod dinosaurs from Asia and North America: Skulls of ''Tarbosaurus bataar'' and ''Tyrannosaurus rex'' compared|journal=Acta Palaeontologica Polonica|volume=48|issue=2|pages=161–190|archive-url=https://web.archive.org/web/20230517131646/https://www.app.pan.pl/archive/published/app48/app48-161.pdf|archive-date=May 17, 2023}}</ref><ref name=Feng2016>{{cite journal|author=Li Feng, Bi Shundong, Michael Pittman, Stephen L. Brusatte, Xu Xing|year=2016|url=https://www.researchgate.net/publication/304145185|title=A new tyrannosaurine specimen (Theropoda: Tyrannosauroidea) with insect borings from the Upper Cretaceous Honglishan Formation of Northwestern China|journal=Cretaceous Research|volume=66|issue=|pages=155–162 |doi=10.1016/j.cretres.2016.06.002|bibcode=2016CrRes..66..155L |hdl=20.500.11820/a49b0878-3ba2-4c3e-b4b1-70fe282e43ea|hdl-access=free}}</ref><ref name=Lucas2018>{{cite journal|author=Sebastian G. Dalman, Spencer G. Lucas|date=January 2018|url=https://www.researchgate.net/publication/328676802|title=Tyrannosaurid dinosaurs (Theropoda: Tyrannosauridae) from the Upper Cretaceous (Early Campanian) Allison Member of the Menefee Formation, New Mexico: Implications for the origin of Tyrannosauridae in North America|series=New Mexico Museum of Natural History and Science Bulletin|journal=Fossil Record|volume=6|issue=79|pages=99–112|doi=}}</ref> The former two taxa were published without detailed descriptions and are therefore nomina nuda. ''T.'' "turpanensis" and ''T. luanchuanensis'' were tentatively listed as [[synonym (taxonomy)|junior synonyms]] of ''Tarbosaurus bataar'' by Holtz in 2004; Holtz also listed ''T.'' "lanpingensis," but as a nomen dubium.<ref name="holtz2004"/><ref name=Feng2016/><ref name=Lucas2018/>

VGI, no. 231/3, a large [[phalanx bone]], assigned to ''Tyrannosaurus'' sp. by Yarkov in 2000, was found in the Lower Maastrichtian of [[Bereslavka, Russia]]. In 2004, Averianov and Yarkov reinterpreted it as a [[metacarpal]] I or [[metatarsal]] I that possibly belongs to [[ceratosaur]].<ref>{{cite journal|author=A. O. Averianov, A. A. Yarkov|year=2004|url=https://repository.geologyscience.ru/bitstream/handle/123456789/39408/Aver_04.pdf?sequence=1|title=Carnivorous dinosaurs (Saurischia, Theropoda) from the Maastrichtian of the Volga-Don Interfluve, Russia|journal=Paleontological Journal|volume=38|issue=1|pages=78–82|archive-url=https://web.archive.org/web/20240305115625/https://repository.geologyscience.ru/bitstream/handle/123456789/39408/Aver_04.pdf?sequence=1|archive-date=March 5, 2024|url-status=live}}</ref> In their 2023 overview, Averianov and Lopatin mention this specimen as well as a single tooth from the same site only as Theropoda indet.<ref>{{cite journal|author=A. O. Averianov, A. V. Lopatin|year=2023|url=https://new.ras.ru/upload/iblock/a8f/vfw1g7hafto3gx7qbnwgpmuljd0j8ykk.pdf#page=45|title=Динозавры России: обзор местонахождений [Dinosaurs of Russia: Overview of locations]|journal=[[Herald of the Russian Academy of Sciences|Vestnik Rossiiskoi Akademii Nauk]]|volume=93|issue=4|pages=342–354|language=ru|doi=10.31857/S0869587323040023|archive-url=https://web.archive.org/web/20240216183756/https://new.ras.ru/upload/iblock/a8f/vfw1g7hafto3gx7qbnwgpmuljd0j8ykk.pdf#page=45|archive-date=February 16, 2024|url-status=live}}</ref>

In 2001, various tyrannosaurid teeth and a metatarsal unearthed in a quarry near [[Zhucheng]], China, were assigned by Chinese paleontologist [[Hu Chengzhi]] to the newly erected species ''Tyrannosaurus zhuchengensis''. However, in a nearby site, a right maxilla and left jawbone were assigned to the newly erected tyrannosaurid genus ''Zhuchengtyrannus'' in 2011. It is possible that ''T. zhuchengensis'' is [[synonym (taxonomy)|synonymous]] with ''Zhuchengtyrannus''. In any case, ''T. zhuchengensis'' is considered to be a ''[[nomen dubium]]'' as the holotype lacks [[diagnosis (taxonomy)|diagnostic]] features below the level Tyrannosaurinae.<ref>{{cite journal|first1=D. W. E.|last1=Hone|first2=K.|last2=Wang|first3=C.|last3=Sullivan|first4=X.|last4=Zhao|first5=S.|last5=Chen|first6=D.|last6=Li|first7=S.|last7=Ji|first8=Q.|last8=Ji|first9=X.|last9=Xu|year=2011|title=A new, large tyrannosaurine theropod from the Upper Cretaceous of China|journal=Cretaceous Research|volume=32|issue=4|pages=495–503|doi=10.1016/j.cretres.2011.03.005|bibcode=2011CrRes..32..495H }}</ref>

In 2006, a fragmentary tyrannosaurid lacrimal (CM 9401) from the [[Judith River Formation]] of Fergus County, Montana, was described as ?''Tyrannosaurus'' sp. This isolated right lacrimal was originally collected alongside the holotype specimen of ''Deinosuchus rugosus'', a giant crocodilian, and remained undescribed until its re-identification as belonging to a tyrannosaurid theropod in the 1980s by paleontologist [[Dale Russell]]. The lacrimal closely resembles those of ''Tyrannosaurus rex'' in both size and morphology. Notably, it lacks the "lacrimal horn" typically present in earlier tyrannosaurids like ''[[Albertosaurus]]'' and ''[[Gorgosaurus]]'', instead exhibiting a distinct rugosity along the dorsal surface—consistent with ''T. rex'' and its Asian relative ''Tarbosaurus''. The specimen's considerable size places it within the range of known ''T. rex'' individuals, suggesting the presence of large tyrannosaurids during the Campanian stage (~75 million years ago), a temporal range earlier than the established Maastrichtian age (~68–66 Ma) for ''Tyrannosaurus rex''. However, the exact age and provenance of CM 9401 remain uncertain due to a lack of detailed field documentation.<ref>{{Cite journal |last1=Urban |first1=Michael A. |last2=Lamanna |first2=Matthew C. |date=December 2006 |title=Evidence of a Giant Tyrannosaurid (Dinosauria: Theropoda) from the Upper Cretaceous (?Campanian) of Montana |url=http://www.bioone.org/doi/abs/10.2992/0097-4463%282006%2975%5B231%3AEOAGTD%5D2.0.CO%3B2 |journal=Annals of Carnegie Museum |language=en |volume=75 |issue=4 |pages=231–235 |doi=10.2992/0097-4463(2006)75[231:EOAGTD]2.0.CO;2 |issn=0097-4463|url-access=subscription }}</ref>

In 2018, a paper describing tyrannosaurid teeth from the Two Medicine Formation noted a premaxillary tooth (YPM VPPU 023469) had a strong resemblance to the teeth of [[Sue (Tyrannosaurus)|Sue]] to the exclusion of any Campanian tyrannosaurid. Additionally, the authors of this paper suggested that CM 9401 also comes from the Two Medicine Formation, as there were preservational similarities between its locality and the Willow Creek anticline, which is where the tooth was found.<ref>{{Cite journal |last1=Dalman |first1=Sebastian G. |last2=Lucas |first2=Spencer G. |last3=Malinzak |first3=D. Edward |date=2018 |title=Tyrannosaurid teeth from the upper Cretaceous (Campanian) Two Medicine Formation of Montana |url=https://www.researchgate.net/publication/328676947 |journal=New Mexico Museum of Natural History and Science Bulletin |volume=79 |issue= |pages=125–139}}</ref> Notably, this would place both specimens in the Flag Butte Member of the Two Medicine Formation, which dates from 77 to 76.3 Ma, far older than any other ''Tyrannosaurus'' specimen, and directly contemporaneous with ''Daspletosaurus.'' In 2025, these specimens, with their old geologic age, were used as evidence by Charlie Scherer to suggest that the Tyrannosaurini did not evolve directly from ''Daspletosaurus''.<ref name=Scherer2025>{{Cite journal |last=Scherer |first=Charlie Roger |date=January 11, 2025 |title=Multiple lines of evidence support anagenesis in Daspletosaurus and cladogenesis in derived tyrannosaurines |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667125000035 |journal=Cretaceous Research |volume=169 |article-number=106080 |doi=10.1016/j.cretres.2025.106080 |bibcode=2025CrRes.16906080S |issn=0195-6671 |archive-date=January 18, 2025 |access-date=January 17, 2025 |archive-url=https://web.archive.org/web/20250118220857/https://linkinghub.elsevier.com/retrieve/pii/S0195667125000035 |url-status=live |url-access=subscription }}</ref>

===''Tyrannosaurus imperator'' and ''Tyrannosaurus regina''===
In a 2022 study, [[Gregory S. Paul]] and colleagues argued that ''Tyrannosaurus rex'', as traditionally understood, actually represents three species: the type species ''Tyrannosaurus rex'', and two previously unrecognized species: ''T. imperator'' (meaning "tyrant lizard emperor") and ''T. regina'' (meaning "tyrant lizard queen"). The holotype of the former (''T. imperator'') is the [[Sue (dinosaur)|Sue]] specimen, and the holotype of the latter (''T. regina'') is [[Wankel rex]]. The division into multiple species was primarily based on the high degree of variation in the proportions and robusticity of the [[femur]] (and other skeletal elements) across ''T. rex'' specimens. Presumed robust and gracile morphotypes and the number of small incisiform teeth in the dentary were also used as a line of evidence. Paul and colleagues categorized the species as follows: ''T. rex'' demonstrates robust anatomy, a moderate ratio of femur length vs circumference, and the possession of a singular slender incisiform dentary tooth, ''T. imperator'' is robust with a small femur length to circumference ratio and two of the slender teeth, and ''T. regina'' is more gracile with a high femur ratio and one of the slender teeth.<ref name="paul2022">{{cite journal | url=https://link.springer.com/article/10.1007/s11692-022-09561-5#Sec12 | title=The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus | last1=Paul | first1=Gregory S. | last2=Persons IV | first2=W. Scott | last3=van Raalte | first3=Jay | journal=Evolutionary Biology | year=2022 | volume=49 | issue=2 | pages=156–179 | doi=10.1007/s11692-022-09561-5 | bibcode=2022EvBio..49..156P | s2cid=247200214 | archive-date=June 12, 2022 | access-date=March 1, 2022 | archive-url=https://web.archive.org/web/20220612011450/https://link.springer.com/article/10.1007/s11692-022-09561-5#Sec12 | url-status=live | url-access=subscription }}</ref>

However, several leading paleontologists, including [[Stephen Brusatte]], [[Thomas Carr (paleontologist)|Thomas Carr]], [[Thomas Holtz]], David Hone, [[Jingmai O'Connor]], and [[Lindsay Zanno]], criticized the study or expressed skepticism of its conclusions when approached by various media outlets for comment.<ref name="newyorktimes">{{cite journal| url=https://www.nytimes.com/2022/02/28/science/tyrannosaurus-rex-species.html? |archive-url=https://web.archive.org/web/20220301014637/https://www.nytimes.com/2022/02/28/science/tyrannosaurus-rex-species.html |archive-date=March 1, 2022 |url-access=subscription |url-status=live | title=They Want to Break T. Rex Into 3 Species. Other Paleontologists Aren't Pleased. | date=February 28, 2022 | journal=The New York Times | access-date=March 1, 2022 | last1=Elbein|first1=Asher}}</ref><ref>{{cite web | url = https://edition.cnn.com/2022/02/28/world/t-rex-three-different-dinosaurs-scn/index.html | title = Tyrannosaurus rex may have been misunderstood | first1 = Katie | last1 = Hunt | date = March 1, 2022 | work = CNN | access-date = March 4, 2022 | archive-date = March 4, 2022 | archive-url = https://web.archive.org/web/20220304034107/https://edition.cnn.com/2022/02/28/world/t-rex-three-different-dinosaurs-scn/index.html | url-status = live }}</ref><ref>{{cite web | url = https://www.nationalgeographic.com/science/article/call-to-split-tyrannosaurus-rex-into-3-species-sparks-fierce-debate | archive-url = https://web.archive.org/web/20220301010250/https://www.nationalgeographic.com/science/article/call-to-split-tyrannosaurus-rex-into-3-species-sparks-fierce-debate | archive-date = March 1, 2022 | title = Call to split T. rex into 3 species sparks fierce debate | work = National Geographic | first1 = Michael | last1 = Greshko | date = March 1, 2022 }}</ref> Their criticism was subsequently published in a technical paper.<ref name="Carr_et.al.(2022)">{{cite journal|last1=Carr|first1=T.D.|last2=Napoli|first2=J.G.|last3=Brusatte|first3=S.L.|last4=Holtz|first4=T.R.|last5=Hone|first5=D.W.E.|last6=Williamson|first6=T.E.|last7=Zanno|first7=L.E.|year=2022|title=Insufficient Evidence for Multiple Species of ''Tyrannosaurus'' in the Latest Cretaceous of North America: A Comment on "The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus ''Tyrannosaurus''"|journal=Evolutionary Biology|volume=49|issue=3|pages=314–341|doi=10.1007/s11692-022-09573-1|doi-access=free|bibcode=2022EvBio..49..327C }}</ref> Holtz and Zanno both remarked that it was plausible that more than one species of ''Tyrannosaurus'' existed, but felt the new study was insufficient to support the species it proposed. Holtz remarked that, even if ''Tyrannosaurus imperator'' represented a distinct species from ''Tyrannosaurus rex'', it may represent the same species as ''Nanotyrannus lancensis'' and would need to be called ''Tyrannosaurus lancensis''. O'Connor, a curator at the Field Museum, where the ''T. imperator'' holotype Sue is displayed, regarded the new species as too poorly-supported to justify modifying the exhibit signs. Brusatte, Carr, and O'Connor viewed the distinguishing features proposed between the species as reflecting natural variation within a species. Both Carr and O'Connor expressed concerns about the study's inability to determine which of the proposed species several well-preserved specimens belonged to. Another paleontologist, [[Philip J. Currie]], originally co-authored the study but withdrew from it as he did not want to be involved in naming the new species.<ref name="newyorktimes"/>

In a subsequent paper published in 2025, Paul maintained the validity of ''T. imperator'' and ''T. regina'', arguing that these proposed species could be further distinguished by the shape of their postorbital bosses (bony rugosities behind the eyes).<ref name="Paul2025">{{Cite journal |last1=Paul |first1=Gregory S. |author1-link=Gregory S. Paul |date=June 30, 2025 |title=A presentation of the current data on the exceptionally diverse non-tyrannosaurid eutyrannosaur and Tyrannosaurini genera and species of western North America during the End Cretaceous North American Interchange |journal=Mesozoic |volume=2 |issue=2 |pages=085–138 |doi=10.11646/mesozoic.2.2.1  |doi-access=free |issn=3021-1867}}</ref>

===''Tyrannosaurus mcraeensis''===
{{multiple image
| align             = right
| direction         = vertical
| image1            = Tyrannosaurus mcraeensis (skull reconstruction).png
| image2            = Tyrannosaurus mcraeensis.png
| footer            = Reconstructed skull (top) and speculative [[life restoration]] (bottom) of ''T. mcraeensis''
}}

In 2024, Dalman and colleagues [[Species description|described]] the remains of a tyrannosaur discovered in 1983 in the Campanian-early Maastrichtian [[Hall Lake Formation]] in New Mexico. Reposited at the [[New Mexico Museum of Natural History and Science]], the fossil material (NMMNH P-3698) consists of the right [[postorbital]], right [[squamosal]], left [[palatine]], and an incomplete [[maxilla]] from the skull, the left [[dentary]], right [[splenial]], right prearticular, right [[Angular bone|angular]] and right [[articular]] from the lower jaws, isolated teeth, and [[Haemal arch|chevron]]s.<ref name=T.mcraeensis>{{Cite journal |last1=Dalman |first1=Sebastian G. |last2=Loewen |first2=Mark A. |last3=Pyron |first3=R. Alexander |last4=Jasinski |first4=Steven E. |last5=Malinzak |first5=D. Edward |last6=Lucas |first6=Spencer G. |last7=Fiorillo |first7=Anthony R. |last8=Currie |first8=Philip J. |last9=Longrich |first9=Nicholas R. |date=January 11, 2024 |title=A giant tyrannosaur from the Campanian–Maastrichtian of southern North America and the evolution of tyrannosaurid gigantism |journal=Scientific Reports |language=en |volume=13 |issue=1 |page=22124 |doi=10.1038/s41598-023-47011-0 |issn=2045-2322|pmid=38212342 |doi-access=free|pmc=10784284 }}</ref> Some of the bones were briefly mentioned in 1984 as belonging to ''T. rex'',<ref name=Lozinsky1984>{{Cite journal |last1=Lozinsky |first1=Richard P. |last2=Hunt |first2=Adrian P. |last3=Wolberg |first3=Donald L. |last4=Lucas |first4=Spencer G. |year=1984 |title=Late Cretaceous (Lancian) dinosaurs from the McRae Formation, Sierra County, New Mexico |journal=New Mexico Geology |language=en |volume=6 |issue=4 |pages=72–77 |doi=10.58799/NMG-v6n4.72 |doi-broken-date=July 12, 2025 |s2cid=237011797 |url=https://geoinfo.nmt.edu/publications/periodicals/nmg/6/n4/nmg_v6_n4_p72.pdf |issn=0196-948X |archive-date=November 18, 2023 |access-date=January 12, 2024 |archive-url=https://web.archive.org/web/20231118063409/http://geoinfo.nmt.edu/publications/periodicals/nmg/6/n4/nmg_v6_n4_p72.pdf |url-status=live }}</ref> and described in 1986.<ref name=Gillette1986>{{Cite journal |last1=Gillette |first1=David D. |last2=Wolberg |first2=Donald L. |last3=Hunt |first3=Adrian P. |year=1986 |title=''Tyrannosaurus rex'' from the McRae Formation (Lancian, Upper Cretaceous), Elephant Butte reservoir, Sierra County, New Mexico |journal=New Mexico Geological Society Guidebook |language=en |volume=37 |pages=235–238 |doi=10.56577/FFC-37.235 |doi-broken-date=July 12, 2025 |s2cid=251985284 |url=https://nmgs.nmt.edu/publications/guidebooks/downloads/37/37_p0235_p0238.pdf |archive-date=January 12, 2024 |access-date=January 12, 2024 |archive-url=https://web.archive.org/web/20240112195843/https://nmgs.nmt.edu/publications/guidebooks/downloads/37/37_p0235_p0238.pdf |url-status=live }}</ref>

Lehman and Carpenter (1990) suggested that NMMNH P-3698 belonged to a new tyrannosaurid genus,<ref>{{cite journal |last=Lehman |first=Thomas M. |author2=Carpenter, Kenneth |author-link2=Kenneth Carpenter |year=1990 |title=A partial skeleton of the tyrannosaurid dinosaur ''Aublysodon'' from the Upper Cretaceous of New Mexico |journal=Journal of Paleontology |volume=64 |issue=6 |pages=1026–1032 |jstor=1305741 |doi=10.1017/S0022336000019843 |bibcode=1990JPal...64.1026L |s2cid=132662000 |url=https://zenodo.org/record/1037493 |archive-date=July 15, 2023 |access-date=March 17, 2024 |archive-url=https://web.archive.org/web/20230715174200/https://zenodo.org/record/1037493 |url-status=live }}</ref> while Carr and Williamson (2000) disagreed with their claim.<ref>{{cite journal | last1 = Carr | first1 = Thomas D. | last2 = Williamson | first2 = Thomas E. | date = 2000 | title = A review of Tyrannosauridae (Dinosauria: Coelurosauria) from New Mexico | publisher = [[New Mexico Museum of Natural History and Science]] | journal = Bulletin | volume = 17 | pages = 113–145 | url = http://econtent.unm.edu/cdm/ref/collection/bulletins/id/1015 }}</ref> Sullivan and Lucas (2015) argued that there is little evidence to support NMMNH P-3698 as a specimen of ''Tyrannosaurus rex'', so they tentatively classified it as cf. ''Tyrannosaurus'' sp.; they also considered that the McRae tyrannosaur lived before the [[Lancian]] (before 67 million years ago) based on its probable association with the ''[[Alamosaurus]]'' fossil.<ref>{{cite journal|last1=Sullivan|first1=Robert M.|last2=Lucas|first2=Spencer G.|year=2015|title=Cretaceous Vertebrates of New Mexico|journal=New Mexico Museum of Natural History and Science Bulletin|volume=68|url=https://www.researchgate.net/publication/299592501}}</ref>

[[File:Tyrannosaurus mcraeensis (mandibular elements).png|thumb|left|upright|Mandibular elements of the ''T. mcraeensis'' holotype]]
Dalman et al. (2024) proposed the new name ''Tyrannosaurus mcraeensis'' for the holotype (NMMNH P-3698), referencing the McRae Group, the rock layers to which the Hall Lake Formation belongs. The holotype of ''T. mcraeensis'' is found in the strata that are around a few million years older than the accepted range of ''T. rex'', which existed at the end of the Maastrichtian. The rock layers were initially estimated to date to between 72.7 and 70.9 Ma, correlating to the latest Campanian or earliest Maastrichtian.<ref name=T.mcraeensis/> However, in a 2024 [[Academic conference|conference]] [[Abstract (summary)|abstract]]s, the specific stratigraphic layer which yielded ''T. mcraeensis'' was estimated to be younger than 69.0 ± 0.4 Ma and older than 66.0 Ma based on the sandstone from the same fossil locality,<ref>{{cite conference|author1=Schantz, E.|author2=Amato, J.M.|author3=Lawton, T.F.|title=Dating dinosaurs in the Laramide foreland: U-Pb geochronologic constraints on a stratigraphic section containing ''Alamosaurus'' and the postulated Tyrannosaurus mcraeensis in the Love Ranch Basin|conference=New Mexico Geological Society of America Abstracts with Programs|volume=56|page=9|url=https://gsa.confex.com/gsa/2024AM/webprogram/Paper405342.html}}</ref> which would suggest that the age of ''T. mcraeensis'' is much closer to ''T. rex'' than previously thought.<ref name=Scherer2025/> ''T. mcraeensis'' was estimated at {{convert|12|m|ft}} long, which is similar to the size of an adult ''T. rex''. The two are distinguished by characters of the skull. Amongst these, the dentary of ''T. mcraeensis'' is proportionately longer and possesses a less prominent chin, and the lower jaw shallower than that of ''T. rex'', suggesting a weaker bite. The teeth are likewise blunter and more laterally compressed, while the post orbital crests are less prominent. Likewise, the skeletal anatomy showcases shared characteristics with ''Tarbosaurus'' and ''Zhuchengtyrannus''.<ref name=T.mcraeensis/><ref name="NYT-20240111">{{cite news |last=Elbein |first=Asher |title=New Origin Story for ''Tyrannosaurus Rex'' Suggested by Fossil - Researchers say the species they named ''Tyrannosaurus mcraeensis'' predated the dinosaur era's great predator. |url=https://www.nytimes.com/2024/01/11/science/new-tyrannosaur-species-fossil.html |date=January 11, 2024 |work=[[The New York Times]] |url-status=live |archive-url=https://archive.today/20240112033027/https://www.nytimes.com/2024/01/11/science/new-tyrannosaur-species-fossil.html |archive-date=January 12, 2024 |access-date=January 12, 2024 }}</ref>

The validity of ''T. mcraeensis'' was subsequently questioned by other researchers in 2025. Morrison and colleagues noted the uncertainty in the previous age estimate of ''T. mcraeensis''. The authors argued that the inclusion of the titanosaurian fossil (cf. ''Alamosaurus'') as a biostratigraphic marker of the Hall Lake Formation fauna makes the dating problematic due to the fossil having a huge variability in assumed sedimentation rates. The study also suggested the uncertainty in the morphology of ''T. mcraeensis'' holotype being reliably outside the known variation of ''T. rex''. Regardless of the age and validity of ''T. mcraeensis'', the authors concluded that the genus ''Tyrannosaurus'' still most likely originated from Laramidia and that the ancestors of this genus possibly migrated from Asia.<ref>{{cite journal|author1=Morrison, C.|author2=Scherer, C.R.|author3=O'Callaghan, E.V.|author4=Layton, C.|author5=Boisvert, C.|author6=Rolando, M.A.|author7=Durrant, L.|author8=Salas, P.|author9=Allain, S.J.R.|author10=Gascoigne, S.J.L.|year=2025|title=Rise of the king: Gondwanan origins and evolution of megaraptoran dinosaurs|journal=Royal Society Open Science|volume=12|issue=5|article-number=242238|doi=10.1098/rsos.242238|doi-access=free|pmid=40337259 |pmc=12055284 |bibcode=2025RSOS...1242238M }}</ref> Later that year, Voris and colleagues regarded ''T. mcraeensis'' as a [[junior synonym]] of ''T. rex'', agreeing with the problematic stratigraphic data and finding all of the proposed diagnostic characters of ''T. mcraeensis'' to be in the known ''T. rex'' specimen range of variation.<ref name="voris25">{{Cite journal |last1=Voris |first1=Jared T. |last2=Zelenitsky |first2=Darla K. |author2-link=Darla Zelenitsky |last3=Kobayashi |first3=Yoshitsugu |author3-link=Yoshitsugu Kobayashi |last4=Modesto |first4=Sean P. |last5=Therrien |first5=François |last6=Tsutsumi |first6=Hiroki |last7=Chinzorig |first7=Tsogtbaatar |last8=Tsogtbaatar |first8=Khishigjav |date=June 11, 2025 |title=A new Mongolian tyrannosauroid and the evolution of Eutyrannosauria |journal=[[Nature (journal)|Nature]] |volume=642 |issue=8069 |pages=973–979 |doi=10.1038/s41586-025-08964-6 |pmid=40500434 |bibcode=2025Natur.642..973V |language=en |issn=0028-0836}} [https://www.nature.com/articles/s41586-025-08964-6#MOESM1 Supplementary Information] {{Webarchive|url=https://web.archive.org/web/20250612101315/https://www.nature.com/articles/s41586-025-08964-6#MOESM1 |date=June 12, 2025 }}</ref> In his study of the ''T. rex'' holotype skull, Carr also did not regard ''T. mcraeensis'' as a valid species, agreeing with the proposed characters of the ''T. mcraeensis'' holotype being visible throughout the hypodigm of ''T. rex''.<ref>{{cite journal|last=Carr|first=Thomas D.|year=2025|title=Observations on the skull of the type specimen of Tyrannosaurus rex Osborn, 1905|journal=All Earth|volume=37|issue=1|pages=1–66|article-number=2539638 |doi=10.1080/27669645.2025.2539638}}</ref>

===''Nanotyrannus''===
{{main|Nanotyrannus}}

[[File:Nanotyrannus lancensis skull.jpg|thumb|Cast of CMNH 7541, the [[holotype]] of ''Nanotyrannus lancensis'', sometimes interpreted as a juvenile ''Tyrannosaurus''.]]
Other tyrannosaur fossils found in the same formations as ''T. rex'' were originally classified as separate taxa, including ''Aublysodon'' and ''Albertosaurus megagracilis'',<ref name="paul1988" /> the latter being named ''Dinotyrannus megagracilis'' in 1995.<ref name="Olshevsky1995">{{Cite journal |last1=Olshevsky |first1=G. |last2=Ford |first2=T.L. |last3=Yamamoto |first3=S. |date=1995 |title=The origin and evolution of the tyrannosaurids |journal=Kyoryugaku Saizensen [Dino Frontline] |volume=9–10 |pages=92–119}}</ref> These fossils are now universally considered to belong to juvenile ''T. rex''.<ref name="carrwilliamson2004">{{Cite journal |last1=Carr |first1=T. D. |last2=Williamson |first2=T. E. |date=2004 |title=Diversity of late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America |journal=Zoological Journal of the Linnean Society |volume=142 |issue=4 |pages=479–523 |doi=10.1111/j.1096-3642.2004.00130.x|doi-access=free }}</ref> A small but nearly complete skull from Montana, {{convert|57.2|cm|ft|sp=us}} long, is an exception. This skull, [[Cleveland Museum of Natural History|CMNH]] 7541, was originally classified as a species of ''[[Gorgosaurus]]'' (''G. lancensis'') by [[Charles W. Gilmore]] in 1946.<ref name="gilmore1946">{{Cite journal |last=Gilmore |first=C. W. |date=1946 |title=A new carnivorous dinosaur from the Lance Formation of Montana |journal=Smithsonian Miscellaneous Collections |volume=106 |pages=1–19}}</ref> In 1988, the specimen was re-described by [[Robert T. Bakker]], Michael Williams, then the curator of paleontology at the Cleveland Museum of Natural History, and [[Philip J. Currie|Phil Currie]], where the original specimen was housed and is now on display. Their initial research indicated that the skull bones were fused, and that it therefore represented an adult specimen. In light of this, Bakker and colleagues assigned the skull to a new genus named ''Nanotyrannus'' (meaning "dwarf tyrant", for its apparently small adult size).<ref name="bakkeretal1988">{{cite journal | last1 = Bakker | first1 = R.T. | last2 = Williams | first2 = M. | last3 = Currie | first3 = P.J. | year = 1988 | title = ''Nanotyrannus'', a new genus of pygmy tyrannosaur, from the latest Cretaceous of Montana | journal = Hunteria | volume = 1 | pages = 1–30 }}</ref> However, in 1999, a detailed analysis by [[Thomas Carr (paleontologist)|Thomas Carr]] revealed the specimen to be a juvenile, leading Carr and many other paleontologists to consider it a juvenile ''T. rex'' individual.<ref name="carr1999">{{cite journal | last1 = Carr | first1 = T.D. | year = 1999 | title = Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria) | url = https://zenodo.org/record/3371479 | journal = Journal of Vertebrate Paleontology | volume = 19 | issue = 3 | pages = 497–520 | doi = 10.1080/02724634.1999.10011161 | bibcode = 1999JVPal..19..497C | s2cid = 83744433 | archive-date = February 20, 2020 | access-date = December 6, 2019 | archive-url = https://web.archive.org/web/20200220183407/https://zenodo.org/record/3371479 | url-status = live }}</ref><ref name=juvenilebataar>{{cite journal | last1 = Tsuihiji | first1 = T. | last2 = Watabe | first2 = M. | last3 = Tsogtbaatar | first3 = K. | last4 = Tsubamoto | first4 = T. | last5 = Barsbold | first5 = R. | last6 = Suzuki | first6 = S. | last7 = Lee | first7 = A.H. | last8 = Ridgely | first8 = R.C. | last9 = Kawahara | first9 = Y. | last10 = Witmer | first10 = L.M. | s2cid = 15369707 | year = 2011 | title = Cranial osteology of a juvenile specimen of ''Tarbosaurus bataar'' from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav, Mongolia | journal = Journal of Vertebrate Paleontology | volume = 31 | issue = 3| pages = 497–517 | doi = 10.1080/02724634.2011.557116 | bibcode = 2011JVPal..31..497T }}</ref>

[[File:Tyrannosaurus Rex Jane.jpg|thumb|left|Reconstructed skeleton of "Jane", [[Burpee Museum of Natural History]]]]
In 2001, a more complete juvenile tyrannosaur (nicknamed "Jane", [[Accession number (cultural property)|accession number]] BMRP 2002.4.1), suggested to belong to the same species as the original ''Nanotyrannus'' specimen, was uncovered. This discovery prompted a conference on tyrannosaurs focused on the issues of the validity of ''Nanotyrannus'', held at the [[Burpee Museum of Natural History]] in 2005. Several paleontologists who had previously published opinions that ''N. lancensis'' was a valid species, including Currie and Williams, saw the discovery of "Jane" as a confirmation that ''Nanotyrannus'' was, in fact, a juvenile ''T. rex''.<ref name=currie2003a>{{cite journal | last1 = Currie | first1 = P.J. | year = 2003a | title = Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada | url = | journal = Acta Palaeontologica Polonica | volume = 48 | issue = | pages = 191–226 }}</ref><ref name="currieetal2005">Currie, Henderson, Horner and Williams (2005). "On tyrannosaur teeth, tooth positions and the taxonomic status of ''Nanotyrannus lancensis''." In "The origin, systematics, and paleobiology of Tyrannosauridae", a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.</ref><ref name="henderson2005">Henderson (2005). "Nano No More: The death of the pygmy tyrant." In "The origin, systematics, and paleobiology of Tyrannosauridae", a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.</ref> [[Peter Larson]] continued to support the hypothesis that ''Nanotyrannus lancensis'' was a separate but closely related species, and also argued that ''[[Stygivenator]]'' (LACM 28471), which is generally considered to be a juvenile of ''Tyrannosaurus rex'', could be a younger specimen of ''Nanotyrannus''.<ref name="larson13">{{cite conference|author=Larson, P.|year=2013|title=The validity of ''Nanotyrannus lancensis'' (Theropoda, Lancian - Upper Maastrichtian of North America|conference=Society of Vertebrate Paleontology 73rd Annual Meeting|page=159|url=https://vertpaleo.org/wp-content/uploads/2021/03/SVP-2013-merged-book-10-15-2013.pdf|access-date=October 31, 2025|archive-date=March 3, 2022|archive-url=https://web.archive.org/web/20220303092634/https://vertpaleo.org/wp-content/uploads/2021/03/SVP-2013-merged-book-10-15-2013.pdf|url-status=live}}</ref><ref>{{cite book|last=Larson|first=P.L.|year=2013|chapter=The case for ''Nanotyrannus''|editor1=Parrish, J.M. |editor2=Molnar, R.A.|editor3=Currie, P.J.|editor4=Koppelhus, E.B.|title=Tyrannosaurid Paleobiology|publisher=University of Indiana Press|pages=15–53|isbn=978-0253009302}}</ref>

In late 2011, news reports about a 2006 discovery of a new, virtually complete theropod specimen found alongside a [[ceratopsid]] were made. The specimens were studied by Robert Bakker and Peter Larson on-site, who identified the ceratopsian as ''[[Triceratops]]'' and the theropod as ''Nanotyrannus''.<ref name="Nano_Smithsonian_2011">{{cite web|author=Black, R.|date=November 10, 2011|title="Montana's "Dueling Dinosaurs"|website=smithsonianmag.com|url=https://www.smithsonianmag.com/science-nature/montanas-dueling-dinosaurs-134669023/|access-date=October 30, 2025|archive-date=July 14, 2025|archive-url=https://web.archive.org/web/20250714000452/https://www.smithsonianmag.com/science-nature/montanas-dueling-dinosaurs-134669023/|url-status=live}}</ref> It was impossible to determine whether the theropod specimen, nicknamed "Bloody Mary", was distinct from ''T. rex'', as the specimen remained in private hands until 2020, when the ownership of the specimen was decided by the [[Montana Supreme Court]] to be given to the landowners Mary Anne and Lige Murray, who agreed to sell the paired fossils to a U.S.-based museum.<ref>{{cite web|author=Cornwall, W.|date=May 22, 2020|title=Court rules ‘Dueling Dinos' belong to landowners, in a win for science|website=science.org|url=https://www.science.org/content/article/court-rules-dueling-dinos-belong-landowners-win-science|access-date=October 30, 2025|archive-date=April 5, 2025|archive-url=https://web.archive.org/web/20250405074109/https://www.science.org/content/article/court-rules-dueling-dinos-belong-landowners-win-science|url-status=live}}</ref> The fossil was acquired by the [[North Carolina Museum of Natural Sciences]] in 2020, after which the museum built an additional research lab space in which to [[Fossil preparation|prepare]], study, and display the specimens.<ref>{{Cite web |last=Pishney |first=Jon |title=North Carolina Museum of Natural Sciences to receive the "Dueling Dinosaurs" |url=https://naturalsciences.org/calendar/news/north-carolina-museum-of-natural-sciences-to-receive-the-dueling-dinosaurs/ |date=November 17, 2020 |access-date=October 31, 2025 |language=en |archive-date=November 18, 2020 |archive-url=https://web.archive.org/web/20201118054601/https://naturalsciences.org/calendar/news/north-carolina-museum-of-natural-sciences-to-receive-the-dueling-dinosaurs/ |url-status=live }}</ref><ref>{{Cite web |last=Pishney |first=Jon |date=October 31, 2023 |title=Dueling Dinosaurs move into the SECU DinoLab {{!}} Programs and Events Calendar |url=https://naturalsciences.org/calendar/news/dueling-dinosaurs-move-into-the-secu-dinolab/ |access-date=October 31, 2025 |language=en |archive-date=June 19, 2024 |archive-url=https://web.archive.org/web/20240619143936/https://naturalsciences.org/calendar/news/dueling-dinosaurs-move-into-the-secu-dinolab/ |url-status=live }}</ref> In 2025, paleontologists [[Lindsay Zanno]] and James Napoli published an initial description of the "Bloody Mary" specimen as part of an extensive revision of the genus ''Nanotyrannus''. They identified this specimen as a skeletally mature individual of ''Nanotyrannus'' and provided several lines of evidence supporting the validity of this genus. They also described a second species, ''N. lethaeus'', based on the Jane specimen due to notable differences between it and ''N. lancensis''.<ref name="Z&N25">{{cite journal |last1=Zanno |first1=Lindsay E. |author1-link=Lindsay Zanno |last2=Napoli |first2=James G. |date=October 30, 2025 |title=''Nanotyrannus'' and ''Tyrannosaurus'' coexisted at the close of the Cretaceous |journal=[[Nature (journal)|Nature]] |doi=10.1038/s41586-025-09801-6 |issn=0028-0836}}</ref>

==Paleobiology==

===Life history===
[[File:Juvenile Tyrannosaurus skull LACM.jpg|left|upright|thumb|Skull of a juvenile ''T. rex'' formerly classified as ''Dinotyrannus megagracilis'']]
The identification of several specimens as juvenile ''T. rex'' has allowed scientists to document [[ontogeny|ontogenetic]] changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The ''Stygivenator'' holotype ([[Los Angeles County Museum of Natural History|LACM]] 28471, the "Jordan theropod"), possibly a juvenile ''T. rex'', is estimated to have weighed only {{cvt|30|kg}}, while the largest adults, such as [[Field Museum of Natural History|FMNH]] PR2081 (Sue) most likely weighed about {{cvt|5650|kg}}. [[Histology|Histologic]] analysis of ''T. rex'' bones showed LACM 28471 had aged only 2 years when it died. Sue was initially estimated at 28 years old, an age which was at the time considered close to the maximum for the species,<ref name="ericksonetal2004" /> but the most recent studies estimate Sue's age at 27–33 years.<ref>{{Cite journal |last1=Cullen |first1=Thomas M. |last2=Canale |first2=Juan I. |last3=Apesteguía |first3=Sebastián |last4=Smith |first4=Nathan D. |last5=Hu |first5=Dongyu |last6=Makovicky |first6=Peter J. |date=November 25, 2020 |title=Osteohistological analyses reveal diverse strategies of theropod dinosaur body-size evolution |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=287 |issue=1939 |article-number=20202258 |doi=10.1098/rspb.2020.2258 |issn=0962-8452 |pmc=7739506 |pmid=33234083}}</ref> Similarly, [[Trix (dinosaur)|Trix (RGM 792.000)]] is estimated to have been at least 30 years old at time of death.<ref>{{Cite web |title=Trix the T. rex is ready for her big Glasgow reveal |url=https://www.gla.ac.uk/news/archiveofnews/2019/april/headline_644272_en.html |access-date=May 23, 2025 |website=www.gla.ac.uk |language=en |archive-date=May 23, 2025 |archive-url=https://web.archive.org/web/20250523204700/https://www.gla.ac.uk/news/archiveofnews/2019/april/headline_644272_en.html |url-status=live }}</ref>

Histology has also allowed the age of other specimens to be determined. Growth curves can be developed when the ages of different specimens are plotted on a graph along with their mass. A ''T. rex'' growth curve is S-shaped, with juveniles remaining under {{cvt|1800|kg}} until approximately 14 years of age, when body size began to increase dramatically. During this rapid growth phase, a young ''T. rex'' would gain an average of {{cvt|600|kg}} a year for the next four years. At 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only {{cvt|600|kg}} separated the 28-year-old Sue from a 22-year-old Canadian specimen ([[Royal Tyrrell Museum of Palaeontology|RTMP]] 81.12.1).<ref name="ericksonetal2004" /> A 2004 histological study performed by different workers corroborates these results, finding that rapid growth began to slow at around 16 years of age.<ref name="hornerpadian2004">{{Cite journal |last1=Horner |first1=J. R. |last2=Padian |first2=K. |date=2004 |title=Age and growth dynamics of Tyrannosaurus rex |journal=Proceedings: Biological Sciences |volume=271 |issue=1551 |pages=1875–80 |doi=10.1098/rspb.2004.2829 |pmc=1691809 |pmid=15347508}}</ref>

[[File:Tyrannosauridae growth rates.svg|thumb|right|A graph showing the hypothesized growth curve, body mass versus age (drawn in black, with other tyrannosaurids for comparison), based on Erickson and colleagues 2004. Studies like this are now known to have been skewed by the inclusion of specimens now considered ''Nanotyrannus'']]
A study by Hutchinson and colleagues in 2011 corroborated the previous estimation methods in general, but their estimation of peak growth rates is significantly higher; it found that the "maximum growth rates for T. rex during the exponential stage are 1790 kg/year".<ref name="Hutchinsonet.al.2011" /> Although these results were much higher than previous estimations, the authors noted that these results significantly lowered the great difference between its actual growth rate and the one which would be expected of an animal of its size.<ref name="Hutchinsonet.al.2011" /> The sudden change in growth rate at the end of the growth spurt may indicate physical maturity, a hypothesis which is supported by the discovery of medullary tissue in the [[femur]] of a 16 to 20-year-old ''T. rex'' from Montana ([[Museum of the Rockies|MOR]] 1125, also known as [[B-rex]]). Medullary tissue is found only in female birds during ovulation, indicating that B-rex was of reproductive age.<ref name="schweitzeretal2005">{{Cite journal |last1=Schweitzer |first1=M. H. |last2=Wittmeyer |first2=J. L. |last3=Horner |first3=J. R. |s2cid=30264554 |date=2005 |title=Gender-specific reproductive tissue in ratites and ''Tyrannosaurus rex'' |journal=Science |volume=308 |issue=5727 |pages=1456–60 |bibcode=2005Sci...308.1456S |doi=10.1126/science.1112158 |pmid=15933198 |url=http://doc.rero.ch/record/14767/files/PAL_E1895.pdf |archive-date=March 12, 2023 |access-date=November 23, 2022 |archive-url=https://web.archive.org/web/20230312052627/https://doc.rero.ch/record/14767/files/PAL_E1895.pdf |url-status=live }}</ref> Further study indicates an age of 18 for this specimen.<ref name="LW08">{{Cite journal |last1=Lee |first1=A. H. |last2=Werning |first2=S. |year=2008 |title=Sexual maturity in growing dinosaurs does not fit reptilian growth models |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=2 |pages=582–587 |bibcode=2008PNAS..105..582L |doi=10.1073/pnas.0708903105 |pmc=2206579 |pmid=18195356|doi-access=free }}</ref> In 2016, it was finally confirmed by Mary Higby Schweitzer and Lindsay Zanno and colleagues that the soft tissue within the femur of MOR 1125 was medullary tissue. This also confirmed the identity of the specimen as a female. The discovery of [[medullary bone]] tissue within ''Tyrannosaurus'' may prove valuable in determining the sex of other dinosaur species in future examinations, as the chemical makeup of medullary tissue is unmistakable.<ref>{{Cite journal |last1=Schweitzer |first1=M. H. |last2=Zheng |first2=W. |last3=Zanno |first3=L. |last4=Werning |first4=S. |last5=Sugiyama |first5=T. |date=2016 |title=Chemistry supports the identification of gender-specific reproductive tissue in Tyrannosaurus rex |journal=Scientific Reports |volume=6 |article-number=23099 |doi=10.1038/srep23099 |pmc=4791554 |pmid=26975806|bibcode=2016NatSR...623099S }}</ref> Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes.<ref name="ericksonetal2006">{{Cite journal |last1=Erickson |first1=G. M. |last2=Currie |first2=P. J. |last3=Inouye |first3=B. D. |last4=Winn |first4=A. A. |s2cid=34191607 |date=2006 |title=Tyrannosaur life tables: an example of nonavian dinosaur population biology |journal=Science |volume=313 |issue=5784 |pages=213–7 |bibcode=2006Sci...313..213E |doi=10.1126/science.1125721 |pmid=16840697}}</ref>

An additional study published in 2020 by Woodward and colleagues, for the journal ''Science Advances'' indicates that during their growth from juvenile to adult, ''Tyrannosaurus'' was capable of slowing down its growth to counter environmental factors such as lack of food. The study, focusing on two juvenile specimens between 13 and 15 years old housed at the Burpee Museum in Illinois, indicates that the rate of maturation for ''Tyrannosaurus'' was dependent on resource abundance. This study also indicates that in such changing environments, ''Tyrannosaurus'' was particularly well-suited to an environment that shifted yearly in regards to resource abundance, hinting that other midsize predators might have had difficulty surviving in such harsh conditions and explaining the niche partitioning between juvenile and adult tyrannosaurs. The study further suggested that ''Tyrannosaurus'' and ''Nanotyrannus'' are synonymous, due to analysis of the growth rings in the bones of the two specimens studied.<ref>{{cite journal|last1=Woodward |first1=Holly N |last2=Tremaine |first2=Katie |last3=Williams |first3=Scott A |last4=Zanno |first4=Lindsay E |last5=Horner |first5=John R |last6=Myhrvold |first6=Nathan |date=January 1, 2020 |title=Growing up Tyrannosaurus rex: Osteohistology refutes the pygmy "Nanotyrannus" and supports ontogenetic niche partitioning in juvenile Tyrannosaurus |volume=6 |issue=1 |article-number=eaax6250 |journal=Science Advances |pmid=31911944 |doi=10.1126/sciadv.aax6250 |pmc=6938697 |bibcode=2020SciA....6.6250W }}</ref><ref>{{cite web|url=https://www.nationalgeographic.com/science/2020/01/nanotyrannus-fossils-really-are-teenage-t-rex-dinosaur-growth-rates/ |archive-url=https://web.archive.org/web/20200101225622/https://www.nationalgeographic.com/science/2020/01/nanotyrannus-fossils-really-are-teenage-t-rex-dinosaur-growth-rates/ |archive-date=January 1, 2020 |last=Greshko |first=Michael |date=January 1, 2020 |title=These sleek predatory dinosaurs really are teenage T. rex |work=[[National Geographic]] |access-date=January 2, 2020}}</ref>

Over half of the known ''T. rex'' specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. One study suggests that the rarity of juvenile ''T. rex'' fossils is due in part to low juvenile mortality rates; the animals were not dying in large numbers at these ages, and thus were not often fossilized. This rarity may also be due to the incompleteness of the [[fossil record]] or to the bias of fossil collectors towards larger, more spectacular specimens.<ref name="ericksonetal2006" /> In a 2013 lecture, Thomas Holtz Jr. suggested that dinosaurs "lived fast and died young" because they reproduced quickly whereas mammals have long lifespans because they take longer to reproduce.<ref name="HoltzLecture2013">{{Cite AV media |url=https://www.youtube.com/watch?v=sqkqkxYGNZc  |archive-url=https://ghostarchive.org/varchive/youtube/20211211/sqkqkxYGNZc| archive-date=December 11, 2021 |url-status=live|title=The Life and Times of Tyrannosaurus rex, with Dr. Thomas Holtz |date=March 19, 2013 |last=Holtz |first=T. R. Jr. |publisher=[[Burke Museum of Natural History and Culture]] |location=Seattle, WA |access-date=October 12, 2013 |orig-date=Lecture held March 8, 2013 |medium=Lecture}}{{cbignore}}</ref> Gregory S. Paul also writes that ''Tyrannosaurus'' reproduced quickly and died young but attributes their short lifespans to the dangerous lives they lived.<ref name="Paul2008Highrisklife">{{Cite book |title=''Tyrannosaurus'', The Tyrant King |last=Paul |first=G. S. |publisher=Indiana University Press |year=2008 |isbn=978-0-253-35087-9 |editor-last=Larson |editor-first=P. L. |pages=307–345 |chapter=Chapter 18: The Extreme Life Style and Habits of the Gigantic Tyrannosaurid Superpredators of the Cretaceous North America and Asia |access-date=September 14, 2013 |editor-last2=Carpenter |editor-first2=K. |chapter-url=https://books.google.com/books?id=5WH9RnfKco4C&pg=PA307}}</ref>

===Skin and possible filamentous feathering===
{{Main|Feathered dinosaur}}

[[File:Wyrex Tyrannosaurus Skin Impression.jpg|thumb|Fossilized skin impressions from the tail region of a ''Tyrannosaurus rex'', [[Houston Museum of Natural Science]]]]
The discovery of [[feathered dinosaur]]s led to debate regarding whether, and to what extent, ''Tyrannosaurus'' might have been feathered.<ref name="Belletal2017" /><ref name="NYT-20190307">{{Cite news |url=https://www.nytimes.com/2019/03/07/arts/design/t-rex-exhibition-american-museum-of-natural-history.html |archive-url=https://web.archive.org/web/20190308002505/https://www.nytimes.com/2019/03/07/arts/design/t-rex-exhibition-american-museum-of-natural-history.html |archive-date=March 8, 2019 |url-access=subscription |url-status=live |title=T. Rex Like You Haven't Seen Him: With Feathers |last=Farago |first=J. |date=March 7, 2019 |work=[[The New York Times]] |access-date=March 7, 2019}}</ref> Filamentous structures, which are commonly recognized as the precursors of [[feather]]s, have been reported in the small-bodied, basal tyrannosauroid ''[[Dilong paradoxus]]'' from the Early Cretaceous [[Yixian Formation]] of China in 2004.<ref name="xuetal2004">{{Cite journal |last1=Xing |first1=X. |last2=Norell |first2=M. A. |last3=Kuang |first3=X. |last4=Wang |first4=X. |last5=Zhao |first5=Q. |last6=Jia |first6=C. |s2cid=4381777 |date=October 7, 2004 |title=Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids |journal=[[Nature (journal)|Nature]] |volume=431 |issue=7009 |pages=680–684 |bibcode=2004Natur.431..680X |doi=10.1038/nature02855 |pmid=15470426 |url=http://doc.rero.ch/record/15283/files/PAL_E2582.pdf |archive-date=January 25, 2023 |access-date=January 23, 2023 |archive-url=https://web.archive.org/web/20230125185242/https://doc.rero.ch/record/15283/files/PAL_E2582.pdf |url-status=live }}</ref> Because [[integument]]ary impressions of larger tyrannosauroids known at that time showed evidence of [[scale (anatomy)|scales]], the researchers who studied ''Dilong'' speculated that insulating feathers might have been lost by larger species due to their smaller surface-to-volume ratio.<ref name="xuetal2004" /> The subsequent discovery of the giant species ''[[Yutyrannus huali]]'', also from the Yixian, showed that even some large tyrannosauroids had feathers covering much of their bodies, casting doubt on the hypothesis that they were a size-related feature.<ref name="yutyrannus">{{Cite journal |last1=Xing |first1=X. |last2=Wang |first2=K. |last3=Zhang |last4=Ma |first4=Q. |last5=Xing |first5=L. |last6=Sullivan |first6=C. |last7=Hu |first7=D. |last8=Cheng |first8=S. |last9=Wang |first9=S. |s2cid=29689629 |date=April 5, 2012 |title=A gigantic feathered dinosaur from the Lower Cretaceous of China |url=http://www.xinglida.net/pdf/Xu_et_al_2012_Yutyrannus.pdf  |journal=Nature |volume=484 |issue=7392 |pages=92–95 |bibcode=2012Natur.484...92X |doi=10.1038/nature10906 |pmid=22481363 |archive-url=https://web.archive.org/web/20120417134949/http://www.xinglida.net/pdf/Xu_et_al_2012_Yutyrannus.pdf |archive-date=April 17, 2012}}</ref> A 2017 study reviewed known skin impressions of tyrannosaurids, including those of a ''Tyrannosaurus'' specimen nicknamed "Wyrex" (HMNS 2006.1743.01, formerly known as BHI 6230) which preserves patches of mosaic scales on the tail, hip, and neck.<ref name="Belletal2017"/> The study concluded that feather covering of large tyrannosaurids such as ''Tyrannosaurus'' was, if present, limited to the upper side of the trunk.<ref name="Belletal2017">{{Cite journal |last1=Bell |first1=P. R. |last2=Campione |first2=N. E. |last3=Persons IV |first3=W. S. |last4=Currie |first4=P. J. |last5=Larson |first5=P. L. |last6=Tanke |first6=D. H. |last7=Bakker |first7=R. T. |date=2017 |title=Tyrannosauroid integument reveals conflicting patterns of gigantism and feather evolution |journal=Biology Letters |volume=13 |issue=6 |article-number=20170092 |doi=10.1098/rsbl.2017.0092|pmid=28592520 |pmc=5493735 }}</ref>

A conference abstract published in 2016 posited that theropods such as ''Tyrannosaurus'' had their upper teeth covered in lips, instead of bare teeth as seen in [[crocodilia]]ns. This was based on the presence of [[Tooth enamel|enamel]], which according to the study needs to remain hydrated, an issue not faced by aquatic animals like crocodilians.<ref name=":0">{{Cite journal |last1=Reisz |first1=R. R. |last2=Larson |first2=D. |year=2016 |title=Dental anatomy and skull length to tooth size ratios support the hypothesis that theropod dinosaurs had lips |url=https://ejournals.library.ualberta.ca/index.php/VAMP/article/download/28196/20702 |journal=4th Annual Meeting, 2016, Canadian Society of Vertebrate Palaeontology |issn=2292-1389 |archive-date=April 4, 2017 |access-date=April 3, 2017 |archive-url=https://web.archive.org/web/20170404043155/https://ejournals.library.ualberta.ca/index.php/VAMP/article/download/28196/20702 |url-status=live }}</ref> However, there has been criticism where it favors the idea for lips, with the 2017 analytical study proposing that tyrannosaurids had large, flat scales on their snouts instead of lips, as modern crocodiles do.<ref name="carr2017">{{Cite journal |last1=Carr |first1=T. D. |last2=Varricchio |first2=D. J. |last3=Sedlmayr |first3=J. C. |last4=Roberts |first4=E. M. |last5=Moore |first5=J. R. |date=March 30, 2017 |title=A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system |journal=Scientific Reports |language=en |volume=7 |article-number=44942 |bibcode=2017NatSR...744942C |doi=10.1038/srep44942 |issn=2045-2322 |pmc=5372470 |pmid=28358353}}</ref><ref name="naish2018">{{Cite web |url=https://blogs.scientificamerican.com/tetrapod-zoology/the-sensitive-face-of-a-big-predatory-dinosaur/ |title=The Sensitive Face of a Big Predatory Dinosaur |last=Naish |first=D. |website=Tetrapod Zoology |publisher=Scientific American Blog Network |access-date=December 5, 2018 |archive-date=December 6, 2018 |archive-url=https://web.archive.org/web/20181206102230/https://blogs.scientificamerican.com/tetrapod-zoology/the-sensitive-face-of-a-big-predatory-dinosaur/ |url-status=live }}</ref> But crocodiles possess rather cracked keratinized skin, not flat scales; by observing the hummocky rugosity of tyrannosaurids, and comparing it to extant lizards, researchers have found that tyrannosaurids had squamose scales rather than a crocodillian-like skin.<ref name="MontevialeCroc">{{cite web |title=Morphology, taxonomy, and phylogenetic relationships of the Monteviale crocodylians (Oligocene, Italy) p. 67 |url=https://scholar.google.com/scholar?hl=en&as_sdt=0%2C14&q=MORPHOLOGY%2C+TAXONOMY%2C+AND+PHYLOGENETIC+RELATIONSHIPS+OF+THE+MONTEVIALE+CROCODYLIANS+%28OLIGOCENE%2C+ITALY%29.&btnG= |website=The Annual Symposium of Vertebrate Palaeontology and Comparative Anatomy |year=2018 |access-date=October 9, 2020 |archive-date=November 10, 2021 |archive-url=https://web.archive.org/web/20211110091020/https://scholar.google.com/scholar?hl=en&as_sdt=0%2C14&q=MORPHOLOGY%2C+TAXONOMY%2C+AND+PHYLOGENETIC+RELATIONSHIPS+OF+THE+MONTEVIALE+CROCODYLIANS+%28OLIGOCENE%2C+ITALY%29.&btnG= |url-status=live }}</ref><ref>{{cite journal |last1=Milinkovitch |first1=Michel |last2=Manukyan |first2=Liana |last3=Debry |first3=Adrien |last4=Di-Poi |first4=Nicolas |last5=Martin |first5=Samuel |last6=Singh |first6=Daljit |last7=Lambert |first7=Dominique |last8=Zwicker |first8=Matthias |title=Crocodile Head Scales Are Not Developmental Units But Emerge from Physical Cracking |journal=Science |date=January 4, 2013 |volume=339 |issue=6115 |pages=78–81 |doi=10.1126/science.1226265 |pmid=23196908 |bibcode=2013Sci...339...78M |s2cid=6859452 |doi-access=free }}</ref>

In 2023, Cullen and colleagues supported the idea that theropods like tyrannosaurids had lips based on anatomical patterns, such as those of the foramina on their face and jaws, more similar to those of modern [[squamate]]s such as [[monitor lizard]]s or [[marine iguana]]s than those of modern [[crocodilia]]ns like [[alligator]]s. Comparison of the teeth of ''Daspletosaurus'' and [[American alligator]]s shows that the enamel of tyrannosaurids had no significant wear and that the teeth of modern crocodilians were eroded on the labial side and were substantially worn. This suggests that it is likely that theropod teeth were kept wet by lips. On the basis of the relationship between hydration and wear resistance, the authors argued that it is unlikely that the teeth of theropods, including tyrannosaurids, would have remained unworn when exposed for a long time, because it would have been hard to maintain hydration. The authors also performed regression analyses to demonstrate the relationship between tooth height and skull length, and found that [[varanid]]s like the [[crocodile monitor]] had substantially greater ratios of tooth height to skull length than those of ''Tyrannosaurus'', indicating that the teeth of theropods were not too big to be covered by extraoral tissues when the mouth was closed.<ref name=CullenEtAl23/>

===Sexual dimorphism===
[[File:MUJA 04.jpg|thumb|upright|left|Skeleton casts mounted in a mating position, [[Jurassic Museum of Asturias]]]]
As the number of known specimens increased, scientists began to analyze the variation between individuals and discovered what appeared to be two distinct body types, or ''morphs'', similar to some other theropod species. As one of these morphs was more solidly built, it was termed the 'robust' morph while the other was termed '[[Wikt:gracile|gracile]]'. Several [[morphology (biology)|morphological]] differences associated with the two morphs were used to analyze [[sexual dimorphism]] in ''T. rex'', with the 'robust' morph usually suggested to be female. For example, the [[pelvis]] of several 'robust' specimens seemed to be wider, perhaps to allow the passage of [[Egg (biology)|eggs]].<ref name="carpenter1990">{{Cite book |title=Dinosaur Systematics: Approaches and Perspectives |last=Carpenter |first=K. |publisher=[[Cambridge University Press]] |year=1992 |isbn=978-0-521-43810-0 |editor-last=Carpenter |editor-first=K. |location=[[Cambridge]] |pages=141–145 |chapter=Variation in ''Tyrannosaurus rex'' |author-link=Kenneth Carpenter |editor-last2=Currie |editor-first2=P. J.}}</ref> It was also thought that the 'robust' morphology correlated with a reduced [[chevron (anatomy)|chevron]] on the first tail vertebra, also ostensibly to allow eggs to pass out of the [[reproductive system|reproductive tract]], as had been erroneously reported for [[crocodile]]s.<ref name="larson1994">{{Cite book |last=Larson |first=P. L. |year=1994 |editor-last=Rosenberg |editor-first=G. D. |editor2-last=Wolberg |editor2-first=D. L. |title=Dino Fest |publisher=The Paleontological Society Special Publications |chapter=''Tyrannosaurus'' sex |volume=7 |pages=139–155}}</ref>

In recent years, evidence for sexual dimorphism has been weakened. A 2005 study reported that previous claims of sexual dimorphism in crocodile chevron anatomy were in error, casting doubt on the existence of similar dimorphism between ''T. rex'' sexes.<ref name="ericksonetal2005">{{Cite journal |last1=Erickson |first1=G. M. |last2=Kristopher |first2=L. A. |last3=Larson |first3=P. |year=2005 |title=Androgynous rex&nbsp;– the utility of chevrons for determining the sex of crocodilians and non-avian dinosaurs |journal=Zoology (Jena, Germany) |volume=108 |issue=4 |pages=277–86 |doi=10.1016/j.zool.2005.08.001 |pmid=16351976 |bibcode=2005Zool..108..277E |url=http://doc.rero.ch/record/14378/files/PAL_E1827.pdf |archive-date=April 4, 2023 |access-date=February 2, 2023 |archive-url=https://web.archive.org/web/20230404163719/https://doc.rero.ch/record/14378/files/PAL_E1827.pdf |url-status=live }}</ref> A full-sized chevron was discovered on the first tail vertebra of Sue, an extremely robust individual, indicating that this feature could not be used to differentiate the two morphs anyway. As ''T. rex'' specimens have been found from [[Saskatchewan]] to [[New Mexico]], differences between individuals may be indicative of geographic variation rather than sexual dimorphism. The differences could also be age-related, with 'robust' individuals being older animals.<ref name="brochu2003" />

Only a single ''Tyrannosaurus'' specimen has been conclusively shown to belong to a specific sex. Examination of B-rex demonstrated the preservation of [[soft tissue]] within several bones. Some of this tissue has been identified as a medullary tissue, a specialized tissue grown only in modern birds as a source of [[calcium]] for the production of [[eggshell]] during [[ovulation]]. As only female birds lay eggs, medullary tissue is only found naturally in females, although males are capable of producing it when injected with female reproductive [[hormone]]s like [[estrogen]]. This strongly suggests that B-rex was female and that she died during ovulation.<ref name="schweitzeretal2005" /> Recent research has shown that medullary tissue is never found in [[crocodilian]]s, which are thought to be the closest living relatives of dinosaurs. The shared presence of medullary tissue in birds and other theropod dinosaurs is further evidence of the close [[evolution]]ary relationship between the two.<ref name="schweitzeretal2007">{{Cite journal |last1=Schweitzer |first1=M. H. |last2=Elsey |first2=R. M. |last3=Dacke |first3=C. G. |last4=Horner |first4=J. R. |last5=Lamm |first5=E. T. |date=2007 |title=Do egg-laying crocodilian (''Alligator mississippiensis'') archosaurs form medullary bone? |journal=Bone |volume=40 |issue=4 |pages=1152–8 |doi=10.1016/j.bone.2006.10.029 |pmid=17223615 }}</ref>

===Posture===
[[File:T. rex old posture.jpg|thumb|Outdated reconstruction (by [[Charles R. Knight]]), showing upright pose]]
Like many [[bipedal]] dinosaurs, ''T. rex'' was historically depicted as a 'living tripod', with the body at 45 degrees or less from the vertical and the tail dragging along the ground, similar to a [[kangaroo]]. This concept dates from [[Joseph Leidy]]'s 1865 reconstruction of ''[[Hadrosaurus]]'', the first to depict a dinosaur in a bipedal posture.<ref name="leidy1865">{{Cite journal |last=Leidy |first=J. |year=1865 |title=Memoir on the extinct reptiles of the Cretaceous formations of the United States |journal=Smithsonian Contributions to Knowledge |volume=14 |pages=1–135}}</ref> In 1915, convinced that the creature stood upright, [[Henry Fairfield Osborn]], former president of the American Museum of Natural History, further reinforced the notion in unveiling the first complete ''T. rex'' skeleton arranged this way. It stood in an upright pose for 77 years, until it was dismantled in 1992.<ref name="amnhsite">{{Cite web |url=http://www.amnh.org/exhibitions/expeditions/treasure_fossil/Treasures/Tyrannosaurus/tyrannos.html?dinos |title=''Tyrannosaurus'' |publisher=[[American Museum of Natural History]] |archive-url=https://web.archive.org/web/20081208143829/http://www.amnh.org/exhibitions/expeditions/treasure_fossil/Treasures/Tyrannosaurus/tyrannos.html?dinos |archive-date=December 8, 2008 |access-date=October 16, 2008}}</ref>

By 1970, scientists realized this pose was incorrect and could not have been maintained by a living animal, as it would have resulted in the [[Dislocation (medicine)|dislocation]] or weakening of several [[joint]]s, including the hips and the articulation between the head and the [[spinal column]].<ref name="newman1970">{{Cite journal |last=Newman |first=B. H. |year=1970 |title=Stance and gait in the flesh-eating ''Tyrannosaurus'' |journal=Biological Journal of the Linnean Society |volume=2 |issue=2 |pages=119–123 |doi=10.1111/j.1095-8312.1970.tb01707.x |url=https://zenodo.org/record/3674749 |archive-date=August 4, 2020 |access-date=March 15, 2020 |archive-url=https://web.archive.org/web/20200804080335/https://zenodo.org/record/3674749 |url-status=live }}</ref> The inaccurate AMNH mount inspired similar depictions in many films and paintings (such as [[Rudolph F. Zallinger|Rudolph Zallinger]]'s famous mural ''[[The Age of Reptiles]]'' in [[Yale University]]'s [[Peabody Museum of Natural History]])<ref>{{Cite web |url=http://peabody.yale.edu/exhibits/age-reptiles-mural |title=The Age of Reptiles Mural |year=2008 |publisher=Yale University |access-date=October 16, 2008 |archive-date=September 29, 2018 |archive-url=https://web.archive.org/web/20180929053007/http://peabody.yale.edu/exhibits/age-reptiles-mural  }}</ref> until the 1990s, when films such as ''[[Jurassic Park (film)|Jurassic Park]]'' introduced a more accurate posture to the general public.<ref>{{Cite journal |last1=Ross |first1=R. M. |last2=Duggan-Haas |first2=D. |last3=Allmon |first3=W. D. |s2cid=162343784 |year=2013 |title=The Posture of ''Tyrannosaurus rex'': Why Do Student Views Lag Behind the Science? |journal=Journal of Geoscience Education |volume=61 |issue=1 |pages=145–160 |bibcode=2013JGeEd..61..145R |doi=10.5408/11-259.1}}</ref> Modern representations in museums, art, and film show ''T. rex'' with its body approximately parallel to the ground with the tail extended behind the body to balance the head.<ref>{{Cite web |url=https://www.aaas.org/tyrannosaurus-rex-not-tripod-anymore |title=''Tyrannosaurus Rex'': Not a tripod anymore |website=American Association for the Advancement of Science |date=April 2, 2013 |access-date=December 5, 2018 |archive-date=December 6, 2018 |archive-url=https://web.archive.org/web/20181206053308/https://www.aaas.org/tyrannosaurus-rex-not-tripod-anymore |url-status=live }}</ref>

To sit down, ''Tyrannosaurus'' may have settled its weight backwards and rested its weight on a pubic boot, the wide expansion at the end of the pubis in some dinosaurs. With its weight rested on the pelvis, it may have been free to move the hindlimbs. Getting back up again might have involved some stabilization from the diminutive forelimbs.<ref>{{Cite web|last=Stevens|first=Kent A.|date=2011|title=Tyrannosaurus rex – "Rex, sit"|url=http://ix.cs.uoregon.edu/~kent/paleontology/Tyrannosaurus/index.html|access-date=July 26, 2020|website=ix.cs.uoregon.edu|archive-date=October 3, 2020|archive-url=https://web.archive.org/web/20201003173931/http://ix.cs.uoregon.edu/~kent/paleontology/Tyrannosaurus/index.html|url-status=live}}</ref><ref name="newman1970"/> The latter known as Newman's pushup theory has been debated. Nonetheless, ''Tyrannosaurus'' was probably able to get up if it fell, which only would have required placing the limbs below the center of gravity, with the tail as an effective counterbalance. Healed stress fractures in the forelimbs have been put forward both as evidence that the arms cannot have been very useful<ref>{{Cite web|title=If T. rex fell, how did it get up, given its tiny arms and low center of gravity?|url=https://www.scientificamerican.com/article/if-t-rex-fell-how-did-it/|access-date=July 26, 2020|website=Scientific American|language=en|archive-date=July 26, 2020|archive-url=https://web.archive.org/web/20200726053130/https://www.scientificamerican.com/article/if-t-rex-fell-how-did-it/|url-status=live}}</ref><ref name="Padian (2022)" /> and as evidence that they were indeed used and acquired wounds,<ref name="Stevens et.al.2008">Stevens K.A., Larson P, Willis E.D. & Anderson A. "Rex, sit: digital modeling of ''Tyrannosaurus rex'' at rest". In Larson P & Carpenter K (eds.). ''Tyrannosaurus rex, the tyrant king'' (Indiana University Press, 2008). p. 192-203</ref> like the rest of the body.

===Arms===
[[File:Tyrannosaurus resting pose.jpg|thumb|left|The forelimbs might have been used to help ''T.&nbsp;rex'' rise from a resting pose, as seen in this cast ([[Bucky (Tyrannosaurus rex)|Bucky]] specimen)]]
When ''T. rex'' was first discovered, the [[humerus]] was the only element of the forelimb known.<ref name="osborn1905">{{Cite journal |last=Osborn |first=H. F. |author-link=Henry Fairfield Osborn |year=1905 |title=''Tyrannosaurus'' and other Cretaceous carnivorous dinosaurs |journal=Bulletin of the AMNH |volume=21 |issue=14 |pages=259–265 |hdl=2246/1464|hdl-access=free }} Retrieved October 6, 2008.</ref> For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of ''[[Allosaurus]]''.<ref name="osborn1917" /> A year earlier, [[Lawrence Lambe]] described the short, two-fingered forelimbs of the closely related ''Gorgosaurus''.<ref name="lambe1914">{{Cite journal |last=Lambe |first=L. M. |author-link=Lawrence Lambe |year=1914 |title=On a new genus and species of carnivorous dinosaur from the Belly River Formation of Alberta, with a description of the skull of ''Stephanosaurus marginatus'' from the same horizon |journal=Ottawa Naturalist |volume=27 |pages=129–135}}</ref> This strongly suggested that ''T. rex'' had similar forelimbs, but this [[hypothesis]] was not confirmed until the first complete ''T. rex'' forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex").<ref name="hornerlessem1993">{{Cite book |title=The complete T. rex |last1=Horner |first1=J. R. |last2=Lessem |first2=D. |publisher=[[Simon & Schuster]] |year=1993 |isbn=978-0-671-74185-3 |location=[[New York City]] |author-link=Jack Horner (paleontologist) |author-link2=Don Lessem |url=https://archive.org/details/completetrexhows00horn }}</ref><ref>{{Cite web|url=https://naturalhistory.si.edu/education/teaching-resources/paleontology/new-view-t-rex|title=A New View of T. Rex {{!}} Smithsonian National Museum of Natural History|date=April 13, 2020|archive-url=https://web.archive.org/web/20200413044033/https://naturalhistory.si.edu/education/teaching-resources/paleontology/new-view-t-rex|access-date=April 13, 2020|archive-date=April 13, 2020}}</ref> The remains of Sue also include complete forelimbs.<ref name="brochu2003" /> ''T. rex'' arms are very small relative to overall body size, measuring only {{convert|1|m|ft|sp=us}} long, and some scholars have labelled them as [[vestigial organs|vestigial]]. However, the bones show large areas for [[muscle]] attachment, indicating considerable strength. This was recognized as early as 1906 by Osborn, who speculated that the forelimbs may have been used to grasp a mate during [[copulation (zoology)|copulation]].<ref name="osborn1906">{{Cite journal |last1=Osborn |first1=H. F. |author-link=Henry Fairfield Osborn |last2=Brown |first2=B. |author-link2=Barnum Brown |year=1906 |title=''Tyrannosaurus'', Upper Cretaceous carnivorous dinosaur |journal=Bulletin of the AMNH |volume=22 |issue=16 |pages=281–296 |hdl=2246/1473}}</ref> Newman (1970) suggested that the forelimbs were used to assist ''Tyrannosaurus'' in rising from a prone position.<ref name="newman1970" /> Since then, other functions have been proposed, although some scholars find them implausible.<ref name="Padian (2022)" /> [[Kevin Padian|Padian]] (2022) argued that the reduction of the arms in tyrannosaurids did not serve a particular function but was a secondary adaptation, stating that as tyrannosaurids developed larger and more powerful skulls and jaws, the arms got smaller to avoid being bitten or torn by other individuals, particularly during group feedings.<ref name="Padian (2022)">Padian K (2022). [https://www.app.pan.pl/archive/published/app67/app009212021.pdf "Why tyrannosaurid forelimbs were so short: An integrative hypothesis"] {{Webarchive|url=https://web.archive.org/web/20220518090424/https://app.pan.pl/archive/published/app67/app009212021.pdf |date=May 18, 2022 }}. ''Acta Palaeontologica Polonica'' '''67'''(1): p. 63-76</ref>
[[File:Tyrannosaur arm 104.JPG|thumb|Diagram illustrating arm anatomy]]
Another possibility is that the forelimbs held struggling prey while it was killed by the tyrannosaur's enormous jaws. This hypothesis may be supported by [[biomechanics|biomechanical]] analysis. ''T. rex'' forelimb bones exhibit extremely thick [[Bone#Structure|cortical bone]], which has been interpreted as evidence that they were developed to withstand heavy loads. The [[biceps brachii]] muscle of an adult ''T. rex'' was capable of lifting {{convert|199|kg|lb|0}} by itself; other muscles such as the [[brachialis]] would work along with the biceps to make elbow flexion even more powerful. The [[M. biceps]] muscle of ''T.&nbsp;rex'' was 3.5 times as powerful as the [[human equivalent]]. A ''T. rex'' forearm had a limited range of motion, with the shoulder and elbow joints allowing only 40 and 45 degrees of motion, respectively. In contrast, the same two joints in ''[[Deinonychus]]'' allow up to 88 and 130 degrees of motion, respectively, while a human arm can rotate 360 degrees at the shoulder and move through 165 degrees at the elbow. The heavy build of the arm bones, strength of the muscles, and limited range of motion may indicate a system evolved to hold fast despite the stresses of a struggling prey animal. In the first detailed scientific description of ''Tyrannosaurus'' forelimbs, paleontologists Kenneth Carpenter and Matt Smith dismissed notions that the forelimbs were useless or that ''Tyrannosaurus'' was an obligate scavenger.<ref name="carpentersmith2001">{{Cite book |title=Mesozoic vertebrate life |last1=Carpenter |first1=K. |last2=Smith |first2=M. |publisher=Indiana University Press |year=2001 |isbn=978-0-253-33907-2 |editor-last=Tanke |editor-first=D. H. |editor-link=Darren Tanke |location=Bloomington |pages=[https://archive.org/details/mesozoicvertebra0000unse/page/90 90–116] |chapter=Forelimb Osteology and Biomechanics of ''Tyrannosaurus rex'' |author-link=Kenneth Carpenter |editor-last2=Carpenter |editor-first2=K. |editor-link2=Kenneth Carpenter |chapter-url=https://archive.org/details/mesozoicvertebra0000unse/page/90}}</ref>

The idea that the arms served as weapons when hunting prey have also been proposed by [[Steven M. Stanley]], who suggested that the arms were used for slashing prey, especially by using the claws to rapidly inflict long, deep gashes to its prey.<ref>{{cite magazine |url=https://news.nationalgeographic.com/2017/11/tyrannosaurus-rex-arms-weapons-paleontology-science/ |archive-url=https://web.archive.org/web/20171102164511/https://news.nationalgeographic.com/2017/11/tyrannosaurus-rex-arms-weapons-paleontology-science/ |archive-date=November 2, 2017 |title=T. Rex's Tiny Arms May Have Been Vicious Weapons |last=Pickrell |first=J. |date=November 2, 2017 |magazine=National Geographic |access-date=December 10, 2018}}</ref> This was dismissed by Padian, who argued that Stanley based his conclusion on incorrectly estimated forelimb size and range of motion.<ref name="Padian (2022)" />

===Thermoregulation===
{{Main|Physiology of dinosaurs}}

[[File:Tyrannosaurus rex mmartyniuk.png|thumb|left|Restoration showing partial feathering]]
''Tyrannosaurus'', like most dinosaurs, was long thought to have an [[ectotherm]]ic ("cold-blooded") reptilian [[metabolism]]. The idea of dinosaur ectothermy was challenged by scientists like [[Robert T. Bakker]] and [[John Ostrom]] in the early years of the "[[Dinosaur Renaissance]]", beginning in the late 1960s.<ref name="bakker1968">{{Cite journal |last=Bakker |first=R. T. |author-link=Robert T. Bakker |year=1968 |title=The superiority of dinosaurs |url=http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/Bakker%201968%20-%20Superiority%20of%20DInos.pdf  |journal=Discovery |volume=3 |issue=2 |pages=11–12 |archive-url=https://web.archive.org/web/20060909131058/http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/Bakker%201968%20-%20Superiority%20of%20DInos.pdf |archive-date=September 9, 2006 |access-date=October 7, 2008}}</ref><ref name="bakker1972">{{Cite journal |last=Bakker |first=R. T. |s2cid=4176132 |author-link=Robert T. Bakker |year=1972 |title=Anatomical and ecological evidence of endothermy in dinosaurs |url=http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/14-%20Bakker%201972%20-%20dino%20endothermy.pdf  |journal=Nature |volume=238 |issue=5359 |pages=81–85 |bibcode=1972Natur.238...81B |doi=10.1038/238081a0 |archive-url=https://web.archive.org/web/20060909173036/http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/14-%20Bakker%201972%20-%20dino%20endothermy.pdf |archive-date=September 9, 2006 |access-date=October 7, 2008}}</ref> ''T. rex'' itself was claimed to have been [[Warm-blooded|endothermic]] ("warm-blooded"), implying a very active lifestyle.<ref name="bakker1986" /> Since then, several paleontologists have sought to determine the ability of ''Tyrannosaurus'' to [[thermoregulation|regulate]] its body temperature. Histological evidence of high growth rates in young ''T. rex'', comparable to those of mammals and birds, may support the hypothesis of a high metabolism. Growth curves indicate that, as in mammals and birds, ''T. rex'' growth was limited mostly to immature animals, rather than the [[indeterminate growth]] seen in most other [[vertebrate]]s.<ref name="hornerpadian2004" />

[[Isotopes of oxygen|Oxygen isotope]] ratios in fossilized bone are sometimes used to determine the temperature at which the bone was deposited, as the ratio between certain isotopes correlates with temperature. In one specimen, the isotope ratios in bones from different parts of the body indicated a temperature difference of no more than {{convert|4|to|5|C-change|0}} between the vertebrae of the torso and the [[tibia]] of the lower leg. This small temperature range between the body core and the extremities was claimed by paleontologist Reese Barrick and [[geochemistry|geochemist]] William Showers to indicate that ''T. rex'' maintained a constant internal body temperature ([[homeotherm]]y) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals.<ref name="barrettshowers1994">{{Cite journal |last1=Barrick |first1=R. E. |last2=Showers |first2=W. J. |s2cid=39392327 |date=1994 |title=Thermophysiology of ''Tyrannosaurus rex'': Evidence from Oxygen Isotopes |journal=[[Science (journal)|Science]] |volume=265 |issue=5169 |pages=222–224 |bibcode=1994Sci...265..222B |doi=10.1126/science.265.5169.222 |pmid=17750663 }}</ref> Other scientists have pointed out that the ratio of oxygen isotopes in the fossils today does not necessarily represent the same ratio in the distant past, and may have been altered during or after fossilization ([[diagenesis]]).<ref name="truemanetal2003">{{Cite journal |last1=Trueman |first1=C. |last2=Chenery |first2=C. |last3=Eberth |first3=D. A. |last4=Spiro |first4=B. |s2cid=130658189 |year=2003 |title=Diagenetic effects on the oxygen isotope composition of bones of dinosaurs and other vertebrates recovered from terrestrial and marine sediments |journal=Journal of the Geological Society |volume=160 |issue=6 |pages=895–901 |doi=10.1144/0016-764903-019 |bibcode=2003JGSoc.160..895T |url=http://doc.rero.ch/record/14987/files/PAL_E2137.pdf |archive-date=April 4, 2023 |access-date=February 2, 2023 |archive-url=https://web.archive.org/web/20230404175035/https://doc.rero.ch/record/14987/files/PAL_E2137.pdf |url-status=live }}</ref> Barrick and Showers have defended their conclusions in subsequent papers, finding similar results in another theropod dinosaur from a different continent and tens of millions of years earlier in time (''[[Giganotosaurus]]'').<ref name="barrickshowers1999">{{Cite journal |last1=Barrick |first1=R. E. |last2=Showers |first2=W. J. |date=1999 |title=Thermophysiology and biology of ''Giganotosaurus'': comparison with ''Tyrannosaurus'' |url=http://palaeo-electronica.org/1999_2/gigan/issue2_99.htm |journal=Palaeontologia Electronica |volume=2 |issue=2 |access-date=October 7, 2008 |archive-date=May 17, 2011 |archive-url=https://web.archive.org/web/20110517220816/http://palaeo-electronica.org/1999_2/gigan/issue2_99.htm  }}</ref> [[Ornithischia]]n dinosaurs also showed evidence of homeothermy, while [[varanidae|varanid]] [[lizard]]s from the same formation did not.<ref name="barrickstevens1997">{{Cite book |title=The Complete Dinosaur |last1=Barrick |first1=R. E. |last2=Stoskopf |first2=M. K. |last3=Showers |first3=W. J. |publisher=Indiana University Press |year=1999 |isbn=978-0-253-21313-6 |editor-last=Farlow |editor-first=J. O. |location=Bloomington |pages=474–490 |chapter=Oxygen isotopes in dinosaur bones |editor-last2=Brett-Surman |editor-first2=M. K.}}</ref> In 2022, Wiemann and colleagues used a different approach—the [[spectroscopy]] of lipoxidation signals, which are byproducts of [[oxidative phosphorylation]] and correlate with metabolic rates—to show that various dinosaur genera including ''Tyrannosaurus'' had endothermic metabolisms, on par with that of modern birds and higher than that of mammals. They also suggested that such a metabolism was ancestrally common to all dinosaurs.<ref name="wiemann2022">{{cite journal |last1=Wiemann |first1=J. |last2=Menéndez |first2=I. |last3=Crawford |first3=J.M. |first4=M. |last4=Fabbri |first5=J.A. |last5=Gauthier |first6=P.M. |last6=Hull |first7=M.A. |last7=Norell |first8=D.E.G. |last8=Briggs |title=Fossil biomolecules reveal an avian metabolism in the ancestral dinosaur |journal=Nature |year=2022 |volume=606 |issue=7914 |pages=522–526 |doi=10.1038/s41586-022-04770-6|pmid=35614213 |bibcode=2022Natur.606..522W |s2cid=249064466 |url=https://resolver.caltech.edu/CaltechAUTHORS:20220531-924660000 }}</ref>

Even if ''T. rex'' does exhibit evidence of homeothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by [[gigantothermy]], as in some living [[sea turtle]]s.<ref name="paladinoetal1997">{{Cite book |title=The Complete Dinosaur |last1=Paladino |first1=F. V. |last2=Spotila |first2=J. R. |last3=Dodson |first3=P. |publisher=Indiana University Press |year=1999 |isbn=978-0-253-21313-6 |editor-last=Farlow |editor-first=J. O. |location=Bloomington |pages=491–504 |chapter=A blueprint for giants: modeling the physiology of large dinosaurs |editor-last2=Brett-Surman |editor-first2=M. K.}}</ref><ref name="chinsamyhillenius2004">{{Cite book |title=The dinosauria |url=https://archive.org/details/dinosauriandedit00weis |url-access=limited |last1=Chinsamy |first1=A. |last2=Hillenius |first2=W. J. |publisher=University of California Press |year=2004 |isbn=978-0-520-24209-8 |editor-last=Weishampel |editor-first=D. B. |location=Berkeley |pages=[https://archive.org/details/dinosauriandedit00weis/page/n661 643]–659 |chapter=Physiology of nonavian dinosaurs |editor-last2=Dodson |editor-first2=P. |editor-last3=Osmólska |editor-first3=H.}}</ref><ref>{{Cite journal |last=Seymour |first=R. S. |date=July 5, 2013 |title=Maximal Aerobic and Anaerobic Power Generation in Large Crocodiles versus Mammals: Implications for Dinosaur Gigantothermy |journal=PLOS ONE |volume=8 |issue=7 |article-number=e69361 |bibcode=2013PLoSO...869361S |doi=10.1371/journal.pone.0069361 |issn=1932-6203 |pmc=3702618 |pmid=23861968|doi-access=free }}</ref> Similar to contemporary crocodilians, openings (dorsotemporal fenestrae) in the skull roofs of ''Tyrannosaurus'' may have aided thermoregulation.<ref name="holliday2019">{{cite journal |last1=Holliday |first1=C.M. |last2=Porter |first2=W.R. |last3=Vilet |first3=K.A. |last4=Witmer |first4=L.M. |year=2019 |title=The Frontoparietal Fossa and Dorsotemporal Fenestra of Archosaurs and Their Significance for Interpretations of Vascular and Muscular Anatomy in Dinosaurs |journal=The Anatomical Record |volume=303 |issue=4 |pages=1060–1074 |doi=10.1002/ar.24218|pmid=31260177 |s2cid=195756776 |doi-access=free }}</ref>

===Soft tissue===
[[File:Tyrannosaurus peptides.jpg|thumb|upright|''T.&nbsp;rex'' femur (MOR 1125) from which demineralized matrix and [[peptides]] (insets) were obtained]]
In the March 2005 issue of ''[[Science (journal)|Science]]'', [[Mary Higby Schweitzer]] of [[North Carolina State University]] and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone from a ''T. rex''. The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue.<ref name="smithsonian-fields">{{Cite magazine |last=Fields |first=H. |date=2006 |title=Dinosaur Shocker |url=http://www.smithsonianmag.com/science-nature/10021606.html |magazine=[[Smithsonian Magazine]] |access-date=October 2, 2008 |archive-date=October 14, 2008 |archive-url=https://web.archive.org/web/20081014011547/http://www.smithsonianmag.com/science-nature/10021606.html  }}</ref> Designated as the Museum of the Rockies specimen 1125, or MOR 1125, the dinosaur was previously excavated from the [[Hell Creek Formation]]. Flexible, bifurcating [[blood vessel]]s and fibrous but elastic [[bone]] matrix tissue were recognized. In addition, microstructures resembling [[blood cell]]s were found inside the matrix and vessels. The structures bear resemblance to [[ostrich]] blood cells and vessels. Whether an unknown process, distinct from normal fossilization, preserved the material, or the material is original, the researchers do not know, and they are careful not to make any claims about preservation.<ref name="MHSetalb">{{Cite journal |last1=Schweitzer |first1=M. H. |last2=Wittmeyer |first2=J. L. |last3=Horner |first3=J. R. |last4=Toporski |first4=J. K. |s2cid=30456613 |date=2005 |title=Soft-tissue vessels and cellular preservation in ''Tyrannosaurus rex'' |journal=[[Science (journal)|Science]] |volume=307 |issue=5717 |pages=1952–5 |bibcode=2005Sci...307.1952S |doi=10.1126/science.1108397 |pmid=15790853 |author-link=Mary Higby Schweitzer}}</ref> If it is found to be original material, any surviving proteins may be used as a means of indirectly guessing some of the DNA content of the dinosaurs involved, because each protein is typically created by a specific gene. The absence of previous finds may be the result of people assuming preserved tissue was impossible, therefore not looking. Since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures.<ref name="smithsonian-fields" /> Research on some of the tissues involved has suggested that birds are closer relatives to tyrannosaurs than other modern animals.<ref>{{Cite news |url=http://news.bbc.co.uk/2/hi/science/nature/6548719.stm |title=Protein links T. rex to chickens |last=Rincon |first=P. |date=April 12, 2007 |work=[[BBC News]] |access-date=October 2, 2008 |archive-date=September 7, 2018 |archive-url=https://web.archive.org/web/20180907082950/http://news.bbc.co.uk/2/hi/science/nature/6548719.stm |url-status=live }}</ref> The original endogenous chemistry was also found in MOR 1125 based on preservation of elements associated with bone remodeling and redeposition (sulfur, calcium, zinc), which showed that the bone cortices are similar to those of extant birds.<ref>{{Cite journal|last1=Anné |first1=J. |last2=Canoville |first2=A. |last3=Edwards |first3=N. P. |last4=Schweitzer |first4=M. H. |last5=Zanno |first5=L. E. |title=Independent Evidence for the Preservation of Endogenous Bone Biochemistry in a Specimen of ''Tyrannosaurus rex'' |year=2023 |journal=Biology |volume=12 |issue=2 |article-number=264 |doi=10.3390/biology12020264 |pmid=36829540 |pmc=9953530 |doi-access=free }}</ref>

In studies reported in ''Science'' in April 2007, Asara and colleagues concluded that seven traces of [[collagen]] proteins detected in purified ''T. rex'' bone most closely match those reported in [[chicken]]s, followed by frogs and newts. The discovery of proteins from a creature tens of millions of years old, along with similar traces the team found in a mastodon bone at least 160,000 years old, upends the conventional view of fossils and may shift paleontologists' focus from bone hunting to biochemistry. Until these finds, most scientists presumed that fossilization replaced all living tissue with inert minerals. Paleontologist Hans Larsson of McGill University in Montreal, who was not part of the studies, called the finds "a milestone", and suggested that dinosaurs could "enter the field of molecular biology and really slingshot paleontology into the modern world".<ref>{{Cite news |url=https://www.usatoday.com/tech/science/discoveries/2007-04-12-trex-protein_N.htm |title=Yesterday's T. Rex is today's chicken |last=Vergano |first=D. |date=April 13, 2007 |work=[[USA Today]] |access-date=October 8, 2008 |archive-date=April 19, 2012 |archive-url=https://web.archive.org/web/20120419005821/http://www.usatoday.com/tech/science/discoveries/2007-04-12-trex-protein_N.htm |url-status=live }}</ref>

The presumed soft tissue was called into question by Thomas Kaye of the [[University of Washington]] and his co-authors in 2008. They contend that what was really inside the tyrannosaur bone was slimy [[biofilm]] created by bacteria that coated the voids once occupied by blood vessels and cells.<ref>{{Cite journal |last1=Kaye |first1=T. G. |last2=Gaugler |first2=G. |last3=Sawlowicz |first3=Z. |date=2008 |editor-last=Stepanova |editor-first=A. |title=Dinosaurian Soft Tissues Interpreted as Bacterial Biofilms |journal=PLOS ONE |volume=3 |issue=7 |article-number=e2808 |bibcode=2008PLoSO...3.2808K |doi=10.1371/journal.pone.0002808 |pmc=2483347 |pmid=18665236|doi-access=free }}</ref> The researchers found that what previously had been identified as remnants of blood cells, because of the presence of iron, were actually [[framboid]]s, microscopic mineral spheres bearing iron. They found similar spheres in a variety of other fossils from various periods, including an [[ammonite]]. In the ammonite, they found the spheres in a place where the iron they contain could not have had any relationship to the presence of blood.<ref>{{Cite press release |title=New Research Challenges Notion That Dinosaur Soft Tissues Still Survive |date=July 24, 2008 |publisher=Newswise |url=http://newswise.com/articles/view/542898/ |access-date=October 8, 2008 |archive-date=July 30, 2017 |archive-url=https://web.archive.org/web/20170730134938/http://newswise.com/articles/view/542898/ |url-status=live }}</ref> Schweitzer has strongly criticized Kaye's claims and argues that there is no reported evidence that biofilms can produce branching, hollow tubes like those noted in her study.<ref>{{Cite press release |title=Researchers Debate: Is It Preserved Dinosaur Tissue, or Bacterial Slime? |date=July 30, 2008 |publisher=Discover |url=http://blogs.discovermagazine.com/80beats/2008/07/30/researchers-debate-is-it-preserved-dinosaur-tissue-or-bacterial-slime/ |access-date=September 4, 2008 |archive-date=August 7, 2008 |archive-url=https://web.archive.org/web/20080807005940/http://blogs.discovermagazine.com/80beats/2008/07/30/researchers-debate-is-it-preserved-dinosaur-tissue-or-bacterial-slime/  }}</ref> San Antonio, Schweitzer and colleagues published an analysis in 2011 of what parts of the collagen had been recovered, finding that it was the inner parts of the collagen coil that had been preserved, as would have been expected from a long period of protein degradation.<ref>{{Cite journal |last1=San Antonio |first1=J. D. |last2=Schweitzer |first2=M. H. |last3=Jensen |first3=S. T. |last4=Kalluri |first4=R. |last5=Buckley |first5=M. |last6=Orgel |first6=J. P. R. O. |date=2011 |editor-last=Van Veen |editor-first=H. W. |title=Dinosaur Peptides Suggest Mechanisms of Protein Survival |journal=PLOS ONE |volume=6 |issue=6 |article-number=e20381 |bibcode=2011PLoSO...620381S |doi=10.1371/journal.pone.0020381 |pmc=3110760 |pmid=21687667|doi-access=free }}</ref> Other research challenges the identification of soft tissue as biofilm and confirms finding "branching, vessel-like structures" from within fossilized bone.<ref>{{Cite journal |last1=Peterson |first1=J. E. |last2=Lenczewski |first2=M. E. |last3=Scherer |first3=R. P. |date=October 12, 2010 |title=Influence of Microbial Biofilms on the Preservation of Primary Soft Tissue in Fossil and Extant Archosaurs |journal=PLOS ONE |volume=5 |issue=10 |article-number=e13334 |bibcode=2010PLoSO...513334P |doi=10.1371/journal.pone.0013334 |pmc=2953520 |pmid=20967227 |quote=[T]he interpretation of preserved organic remains as microbial biofilm [is] highly unlikely|doi-access=free }}</ref>

===Speed===
{{Annotated image/Skeletal anatomy of T rex right leg | float=left}}
Scientists have produced a wide range of possible maximum running speeds for ''Tyrannosaurus'': mostly around {{convert|9|m/s|km/h mph|sp=us}}, but as low as {{convert|4.5|–|6.8|m/s|km/h mph|sp=us}} and as high as {{convert|20|m/s|km/h mph|sp=us}}, though it running at this speed is very unlikely. ''Tyrannosaurus'' was a bulky and heavy carnivore so it is unlikely to run very fast at all compared to other theropods like ''[[Carnotaurus]]'' or ''[[Giganotosaurus]]''.<ref name="HutchinsonGarcia2002TrexSlow">{{Cite journal |last1=Hutchinson |first1=J. R. |last2=Garcia |first2=M. |s2cid=4389633 |date=2002 |title=''Tyrannosaurus'' was not a fast runner |journal=Nature |volume=415 |issue=6875 |pages=1018–21 |bibcode=2002Natur.415.1018H |doi=10.1038/4151018a |pmid=11875567 |url=http://researchonline.rvc.ac.uk/id/eprint/1204/ |archive-date=August 9, 2022 |access-date=January 23, 2023 |archive-url=https://web.archive.org/web/20220809012102/https://researchonline.rvc.ac.uk/id/eprint/1204/ |url-status=live |url-access=subscription }}</ref> Researchers have relied on various estimating techniques because, while there are many [[trackway|tracks]] of large theropods walking, none showed evidence of running.<ref name="Hutchinson2004">{{Cite journal |last=Hutchinson |first=J. R. |year=2004 |title=Biomechanical Modeling and Sensitivity Analysis of Bipedal Running Ability. II. Extinct Taxa |url=http://www.rvc.ac.uk/AboutUs/Staff/jhutchinson/documents/JRH13.pdf  |journal=Journal of Morphology |volume=262 |issue=1 |pages=441–461 |doi=10.1002/jmor.10240 |pmid=15352202 |bibcode=2004JMorp.262..441H |s2cid=15677774 |archive-url=https://web.archive.org/web/20081031093050/http://www.rvc.ac.uk/AboutUs/Staff/jhutchinson/documents/JRH13.pdf |archive-date=October 31, 2008}}</ref>

A 2002 report used a mathematical model (validated by applying it to three living animals: [[alligator]]s, [[chicken]]s, and [[human]]s; and eight more species, including emus and ostriches<ref name="Hutchinson2004" />) to gauge the leg muscle mass needed for fast running (over {{convert|40|km/h|mph|disp=or|abbr=on}}).<ref name="HutchinsonGarcia2002TrexSlow" /> Scientists who think that ''Tyrannosaurus'' was able to run point out that hollow bones and other features that would have lightened its body may have kept adult weight to a mere {{convert|4.5|MT|ST}} or so, or that other animals like [[ostrich]]es and [[horse]]s with long, flexible legs are able to achieve high speeds through slower but longer strides.<ref name="Hutchinson2004" /> Proposed top speeds exceeded {{convert|40|km/h|mph|sp=us}} for ''Tyrannosaurus'', but were deemed infeasible because they would require exceptional leg muscles of approximately 40–86%&nbsp;of total body mass. Even moderately fast speeds would have required large leg muscles. If the muscle mass was less, only {{convert|18|km/h|mph|sp=us}} for walking or jogging would have been possible.<ref name="HutchinsonGarcia2002TrexSlow" /> Holtz noted that tyrannosaurids and some closely related groups had significantly longer [[distal]] hindlimb components (shin plus foot plus toes) relative to the femur length than most other theropods, and that tyrannosaurids and their close relatives had a tightly interlocked [[metatarsus]] (foot bones).<ref name="Holtz1998TaxonomyCoelurosauria">{{Cite journal |last=Holtz |first=T. R. |author-link=Thomas R. Holtz Jr. |date=May 1, 1996 |title=Phylogenetic taxonomy of the Coelurosauria (Dinosauria; Theropoda) |url=http://jpaleontol.geoscienceworld.org/cgi/content/abstract/70/3/536 |journal=[[Journal of Paleontology]] |volume=70 |issue=3 |pages=536–538 |doi=10.1017/S0022336000038506 |bibcode=1996JPal...70..536H |s2cid=87599102 |access-date=October 3, 2008 |archive-date=October 26, 2008 |archive-url=https://web.archive.org/web/20081026053239/http://jpaleontol.geoscienceworld.org/cgi/content/abstract/70/3/536 |url-status=live |url-access=subscription }}</ref> The third metatarsal was squeezed between the second and fourth metatarsals to form a single unit called an [[arctometatarsal|arctometatarsus]]. This ankle feature may have helped the animal to run more efficiently.<ref>{{Cite book |url=https://books.google.com/books?id=VThUUUtM8A4C&q=tyrannosaurus+metatarsals+squeezing&pg=PA193 |title=Vertebrate Palaeontology |last=Benton |first=M. |year=2014 |isbn=978-1-118-40755-4 |edition=4th |page=193|publisher=John Wiley & Sons }}</ref> Together, these leg features allowed ''Tyrannosaurus'' to transmit locomotory forces from the foot to the lower leg more effectively than in earlier theropods.<ref name="Holtz1998TaxonomyCoelurosauria" />  
[[File:Tyrannosaurid trackway.png|thumb|Only known tyrannosaurid trackway (''[[Bellatoripes fredlundi]]''), from the [[Wapiti Formation]], [[British Columbia]]]]

Additionally, a 2020 study indicates that ''Tyrannosaurus'' and other tyrannosaurids were exceptionally efficient walkers. Studies by Dececchi et al., compared the leg proportions, body mass, and the gaits of more than 70 species of theropod dinosaurs including ''Tyrannosaurus'' and its relatives. The research team then applied a variety of methods to estimate each dinosaur's top speed when running as well as how much energy each dinosaur expended while moving at more relaxed speeds such as when walking. Among smaller to medium-sized species such as dromaeosaurids, longer legs appear to be an adaptation for faster running, in line with previous results by other researchers. But for theropods weighing over {{convert|1000|kg|lb|abbr=on}}, top running speed is limited by body size, so longer legs instead were found to have correlated with low-energy walking. The results further indicate that smaller theropods evolved long legs as a means to both aid in hunting and escape from larger predators while larger theropods that evolved long legs did so to reduce the energy costs and increase foraging efficiency, as they were freed from the demands of predation pressure due to their role as apex predators. Compared to more basal groups of theropods in the study, tyrannosaurs like ''Tyrannosaurus'' itself showed a marked increase in foraging efficiency due to reduced energy expenditures during hunting or scavenging. This in turn likely resulted in tyrannosaurs having a reduced need for hunting forays and requiring less food to sustain themselves as a result. Additionally, the research, in conjunction with studies that show tyrannosaurs were more agile than other large-bodied theropods, indicates they were quite well-adapted to a long-distance stalking approach followed by a quick burst of speed to go for the kill. Analogies can be noted between tyrannosaurids and modern wolves as a result, supported by evidence that at least some tyrannosaurids were hunting in group settings.<ref>{{Cite journal|title=The fast and the frugal: Divergent locomotory strategies drive limb lengthening in theropod dinosaurs |first1=T. Alexander |last1=Dececchi |first2=Aleksandra M. |last2=Mloszewska |first3=Thomas R. Jr. |last3=Holtz |first4=Michael B. |last4=Habib |first5=Hans C. E. |last5=Larsson |date=May 13, 2020 |journal=PLOS ONE |volume=15 |issue=5 |article-number=e0223698 |doi=10.1371/journal.pone.0223698 |pmid=32401793 |pmc=7220109 |bibcode = 2020PLoSO..1523698D |doi-access=free}}</ref><ref>{{cite news |title=T. rex was a champion walker, super-efficient at lower speeds |url=https://www.eurekalert.org/news-releases/500578 |access-date=August 16, 2023 |work=EurekAlert! |date=May 13, 2020 |language=en |archive-date=August 16, 2023 |archive-url=https://web.archive.org/web/20230816101705/https://www.eurekalert.org/news-releases/500578 |url-status=live }}</ref>

A study published in 2021 by Pasha van Bijlert et al., calculated the [[preferred walking speed]] of ''Tyrannosaurus'', reporting a speed of {{convert|1.28|m/s|km/h mph|sp=us}}. While walking, animals reduce their [[cost of transport|energy expenditure]] by choosing certain step rhythms at which their body parts [[resonate]]. The same would have been true for [[dinosaurs]], but previous studies did not fully account for the impact the tail had on their walking speeds. According to the authors, when a dinosaur walked, its tail would slightly sway up and down with each step as a result of the [[interspinous ligaments]] suspending the tail. Like rubber bands, these ligaments stored energy when they are stretched due to the swaying of the tail. Using a 3-D model of ''Tyrannosaurus'' specimen [[Trix (dinosaur)|Trix]], muscles and ligaments were reconstructed to simulate the tail movements. This results in a rhythmic, energy-efficient walking speed for ''Tyrannosaurus'' similar to that seen in living animals such as humans, ostriches and giraffes.<ref name=vanBijlert2021>{{cite journal |author1=van Bijlert, P. A. |author2=van Soest, A. J. K. |author3=Schulp, A. S. |title=Natural Frequency Method: estimating the preferred walking speed of ''Tyrannosaurus rex'' based on tail natural frequency. |journal=Royal Society Open Science |volume=8 |issue=4 |article-number=201441 |year=2021 |doi=10.1098/rsos.201441 |pmid=33996115 |pmc=8059583 |bibcode=2021RSOS....801441V |s2cid=233312053 |url=https://phys.org/news/2021-04-dinosaur-biomechanical-tyrannosaurus-rex-gait.html |archive-date=April 22, 2021 |access-date=April 22, 2021 |archive-url=https://web.archive.org/web/20210422224520/https://phys.org/news/2021-04-dinosaur-biomechanical-tyrannosaurus-rex-gait.html |url-status=live }}</ref>

A 2017 study estimated the top running speed of ''Tyrannosaurus'' as {{convert|17|mph|km/h|abbr=on}}, speculating that ''Tyrannosaurus'' exhausted its energy reserves long before reaching top speed, resulting in a parabola-like relationship between size and speed.<ref>{{Cite web |url=https://www.sciencedaily.com/releases/2017/07/170717115657.htm |title=Why ''Tyrannosaurus'' was a slow runner and why the largest are not always the fastest |date=July 17, 2017 |website=ScienceDaily |language=en |access-date=November 10, 2017 |archive-date=April 2, 2019 |archive-url=https://web.archive.org/web/20190402111657/https://www.sciencedaily.com/releases/2017/07/170717115657.htm |url-status=live }}</ref><ref>{{Cite journal |last1=Hirt |first1=M. R. |last2=Jetz |first2=W. |last3=Rall |first3=B. C. |last4=Brose |first4=U. |s2cid=425473 |date=2017 |title=A general scaling law reveals why the largest animals are not the fastest. |journal=Nature Ecology & Evolution |volume=1 |issue=8 |pages=1116–1122 |doi=10.1038/s41559-017-0241-4 |pmid=29046579|bibcode=2017NatEE...1.1116H }}</ref> Another 2017 study hypothesized that an adult ''Tyrannosaurus'' was incapable of running due to high skeletal loads. Using a calculated weight estimate of 7&nbsp;tons, the model showed that speeds above {{convert|11|mph|km/h|abbr=on}} would have probably shattered the leg bones of ''Tyrannosaurus''. The finding may mean that running was also not possible for other giant theropod dinosaurs like ''[[Giganotosaurus]]'', ''[[Mapusaurus]]'' and ''[[Acrocanthosaurus]]''.<ref>{{Cite journal |last1=Sellers |first1=W. I. |last2=Pond |first2=S. B. |last3=Brassey |first3=C. A. |last4=Manning |first4=P. L. |last5=Bates |first5=K. T. |date=July 18, 2017 |title=Investigating the running abilities of ''Tyrannosaurus rex'' using stress-constrained multibody dynamic analysis |journal=PeerJ |language=en |volume=5 |article-number=e3420 |doi=10.7717/peerj.3420 |issn=2167-8359 |pmc=5518979 |pmid=28740745 |doi-access=free }}</ref>
However, studies by Eric Snively and colleagues'','' published in 2019 indicate that ''Tyrannosaurus'' and other tyrannosaurids were more maneuverable than allosauroids and other theropods of comparable size due to low rotational inertia compared to their body mass combined with large leg muscles. As a result, it is hypothesized that ''Tyrannosaurus'' was capable of making relatively quick turns and could likely pivot its body more quickly when close to its prey, or that while turning, the theropod could "pirouette" on a single planted foot while the alternating leg was held out in a suspended swing during a pursuit. The results of this study potentially could shed light on how agility could have contributed to the success of tyrannosaurid evolution.<ref>{{Cite journal |last1=Cotton |first1=J. R. |last2=Hartman |first2=S. A. |last3=Currie |first3=P. J. |last4=Witmer |first4=L. M. |last5=Russell |first5=A. P. |last6=Holtz |first6=T. R. Jr. |last7=Burns |first7=M. E. |last8=Surring |first8=L. A. |last9=Mallison |first9=H. |date=February 21, 2019 |title=Lower rotational inertia and larger leg muscles indicate more rapid turns in tyrannosaurids than in other large theropods |journal=PeerJ |volume=7 |article-number=e6432 |doi=10.7717/peerj.6432 |pmid=30809441 |pmc=6387760 |first10=D. M. |last10=Henderson |first11=H. |last11=O'Brien |first12=E. |last12=Snively |doi-access=free }}</ref>

===Possible footprints===
[[File:Philmont T-Rex 2022.jpg|right|thumb|Probable footprint from [[New Mexico]]]]
Two isolated fossilized [[footprint]]s have been tentatively assigned to ''T. rex''. The first was discovered at [[Philmont Scout Ranch]], New Mexico, in 1983 by American geologist Charles Pillmore. Originally thought to belong to a [[hadrosaurid]], examination of the footprint revealed a large 'heel' unknown in [[ornithopod]] dinosaur tracks, and traces of what may have been a [[hallux]], the dewclaw-like fourth digit of the tyrannosaur foot. The footprint was published as the [[ichnogenus]] ''[[Tyrannosauripus pillmorei]]'' in 1994, by [[Martin Lockley]] and Adrian Hunt. Lockley and Hunt suggested that it was very likely the track was made by a ''T. rex'', which would make it the first known footprint from this species. The track was made in what was once a vegetated wetland mudflat. It measures {{convert|83|cm|in|sp=us}} long by {{convert|71|cm|in|sp=us}} wide.<ref name="lockley&hunt1994">{{Cite journal |last1=Lockley |first1=M. G. |last2=Hunt |first2=A. P. |year=1994 |title=A track of the giant theropod dinosaur ''Tyrannosaurus'' from close to the Cretaceous/Tertiary boundary, northern New Mexico |journal=Ichnos |volume=3 |issue=3 |pages=213–218  |doi=10.1080/10420949409386390|bibcode=1994Ichno...3..213L }}</ref>

A second footprint that may have been made by a ''Tyrannosaurus'' was first reported in 2007 by British paleontologist Phil Manning, from the [[Hell Creek Formation]] of Montana. This second track measures {{convert|72|cm|in|sp=us}} long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by ''Tyrannosaurus'' is unclear, though ''Tyrannosaurus'' is the only large theropod known to have existed in the Hell Creek Formation.<ref name="rextrack2007">{{Cite web |url=http://www.nhm.ac.uk/about-us/news/2007/october/news_12515.html |title=A Probable Tyrannosaurid Track From the Hell Creek Formation (Upper Cretaceous), Montana, United States |year=2007 |website=National Museum of History News  |access-date=December 18, 2007 |archive-url=https://web.archive.org/web/20071214014855/http://www.nhm.ac.uk/about-us/news/2007/october/news_12515.html |archive-date=December 14, 2007 }}</ref><ref name="manningetal2008">{{Cite journal |last1=Manning |first1=P. L. |last2=Ott |first2=C. |last3=Falkingham |first3=P. L. |s2cid=129985735 |year=2009 |title=The first tyrannosaurid track from the Hell Creek Formation (Late Cretaceous), Montana, U.S.A |journal=PALAIOS |volume=23 |issue=10 |pages=645–647 |bibcode=2008Palai..23..645M |doi=10.2110/palo.2008.p08-030r}}</ref>

A set of footprints in Glenrock, Wyoming dating to the [[Maastrichtian]] stage of the Late Cretaceous and hailing from the [[Lance Formation]] were described by Scott Persons, Phil Currie and colleagues in 2016, and are believed to belong to either a juvenile ''T. rex'' or ''Nanotyrannus lancensis''. From measurements and based on the positions of the footprints, the animal was believed to be traveling at a walking speed of around 2.8 to 5 miles per hour and was estimated to have a hip height of {{convert|1.56|to|2.06|m|ft|abbr=on}}.<ref>{{Cite journal |last1=Smith |first1=S. D. |last2=Persons |first2=W. S. |last3=Xing |first3=L. |year=2016 |title=A "Tyrannosaur" trackway at Glenrock, Lance Formation (Maastrichtian), Wyoming |url=https://www.sciencedaily.com/releases/2016/01/160116214746.htm |journal=Cretaceous Research |volume=61 |issue=1 |pages=1–4 |doi=10.1016/j.cretres.2015.12.020 |bibcode=2016CrRes..61....1S |archive-date=July 11, 2019 |access-date=March 9, 2018 |archive-url=https://web.archive.org/web/20190711130653/https://www.sciencedaily.com/releases/2016/01/160116214746.htm |url-status=live |url-access=subscription }}</ref><ref>{{Cite journal |last=Perkins |first=S. |year=2016 |title=You could probably have outrun a ''T. rex'' |url=https://www.science.org/content/article/you-could-probably-have-outrun-t-rex |journal=Palaeontology |doi=10.1126/science.aae0270 |archive-date=October 3, 2022 |access-date=June 30, 2022 |archive-url=https://web.archive.org/web/20221003205139/https://www.science.org/content/article/you-could-probably-have-outrun-t-rex |url-status=live |url-access=subscription }}</ref><ref>{{cite news |url=https://www.usatoday.com/story/news/2016/01/27/tyrannosaurs-faster-than-velociraptors/79423372/ |title=Forget all you know from Jurassic Park: For speed, ''T. rex'' beats ''velociraptor''s |last=Walton |first=T. |access-date=March 13, 2016 |newspaper=USA Today |year=2016 |archive-date=August 19, 2018 |archive-url=https://web.archive.org/web/20180819045903/https://www.usatoday.com/story/news/2016/01/27/tyrannosaurs-faster-than-velociraptors/79423372/ |url-status=live }}</ref> A follow-up paper appeared in 2017, increasing the speed estimations by 50–80%.<ref>{{Cite journal |last=Ruiz |first=J. |year=2017 |title=Comments on "A tyrannosaur trackway at Glenrock, Lance Formation (Maastrichtian), Wyoming" (Smith et al., ''Cretaceous Research'', v. 61, pp. 1–4, 2016) |journal=Cretaceous Research |volume=82 |pages=81–82 |doi=10.1016/j.cretres.2017.05.033}}</ref>

Rare fossil footprints and trackways found in New Mexico and Wyoming that are assigned to the ichnogenus ''[[Tyrannosauripus]]'' have been attributed to being made by ''Tyrannosaurus'', based on the stratigraphic age of the rocks they are preserved in. The first specimen, found in 1994 was described by Lockley and Hunt and consists of a single, large footprint. Another pair of ichnofossils, described in 2021, show a large tyrannosaurid rising from a prone position by rising up using its elbows in conjunction with the pads on their feet to stand. These two unique sets of fossils were found in Ludlow, Colorado and Cimarron, New Mexico.<ref>{{cite journal|url=https://www.researchgate.net/publication/348002331|last1=Caneer|first1=T.|last2=Molkestad|first2=T.|last3=Lucas|first3=S.G.|title=TRACKS IN THE UPPER CRETACEOUS OF THE RATON BASIN POSSIBLY SHOW TYRANNOSAURID RISING FROM A PRONE POSITION|journal=New Mexico Museum of Natural History and Science|year=2021|pages=29–37}}</ref> Another ichnofossil described in 2018, perhaps belonging to a juvenile ''Tyrannosaurus'' or ''Nanotyrannus'' was uncovered in the Lance Formation of Wyoming. The trackway itself offers a rare glimpse into the walking speed of tyrannosaurids, and the trackmaker is estimated to have been moving at a speed of {{convert|4.5-8.0|km/h|mph|sp=us}}, significantly faster than previously assumed for estimations of walking speed in tyrannosaurids.<ref>{{cite journal|url=https://www.sciencedirect.com/science/article/abs/pii/S0195667115301452|last1=Smith|first1=S.D|last2=Persons|first2=W.S.|last3=Xing|first3=Lida|title=A tyrannosaur trackway at Glenrock, Lance Formation (Maastrichtian), Wyoming|year=2016|journal=Cretaceous Research|volume=61|pages=1–4|doi=10.1016/j.cretres.2015.12.020|bibcode=2016CrRes..61....1S|archive-date=April 22, 2021|access-date=January 3, 2021|archive-url=https://web.archive.org/web/20210422134259/https://www.sciencedirect.com/science/article/abs/pii/S0195667115301452|url-status=live|url-access=subscription}}</ref><ref>{{cite journal|url=http://westerndigs.org/tyrannosaur-tracks-discovered-in-wyoming-reveal-dinosaurs-speed/|title=Tyrannosaur Tracks Discovered in Wyoming Reveal Dinosaur's Speed|last=De Pastino|first=B.|journal=Western Digs|year=2016|volume=61|pages=1–4|doi=10.1016/j.cretres.2015.12.020|bibcode=2016CrRes..61....1S|access-date=January 3, 2021|archive-date=January 18, 2021|archive-url=https://web.archive.org/web/20210118041135/http://westerndigs.org/tyrannosaur-tracks-discovered-in-wyoming-reveal-dinosaurs-speed/|url-access=subscription}}</ref>

=== Brain and senses ===
[[File:Sue TRex Skull Full Frontal.JPG|thumb|upright|left|The eye-sockets faced mainly forwards, giving it good [[binocular vision]] ([[Sue specimen]]).]]
A study conducted by [[Lawrence Witmer]] and Ryan Ridgely of Ohio University found that ''Tyrannosaurus'' shared the heightened sensory abilities of other [[coelurosaur]]s, highlighting relatively rapid and coordinated eye and head movements; an enhanced ability to sense low frequency sounds, which would allow tyrannosaurs to track prey movements from long distances; and an enhanced sense of smell.<ref name="witmer2009">{{Cite journal |last1=Witmer |first1=L. M. |last2=Ridgely |first2=R. C. |date=2009 |title=New Insights into the Brain, Braincase, and Ear Region of Tyrannosaurs (Dinosauria, Theropoda), with Implications for Sensory Organization and Behavior |journal=The Anatomical Record |volume=292 |issue=9 |pages=1266–1296 |doi=10.1002/ar.20983 |pmid=19711459|s2cid=17978731 |doi-access=free }}</ref> A study published by Kent Stevens concluded that ''Tyrannosaurus'' had keen vision. By applying modified [[perimetry]] to facial reconstructions of several dinosaurs including ''Tyrannosaurus'', the study found that ''Tyrannosaurus'' had a binocular range of 55 degrees, surpassing that of modern hawks. Stevens estimated that ''Tyrannosaurus'' had 13 times the visual acuity of a human and surpassed the visual acuity of an eagle, which is 3.6 times that of a person. Stevens estimated a limiting far point (that is, the distance at which an object can be seen as separate from the horizon) as far as {{convert|6|km|mi|sp=us|abbr=on}} away, which is greater than the {{convert|1.6|km|mi|0|sp=us|abbr=on}} that a human can see.<ref name="Stevens2006Binocular"/><ref name="jaffe" /><ref name="stevenswebpage">{{Cite web |url=http://ix.cs.uoregon.edu/~kent/paleontology/binocularVision/ |title=The Binocular Vision of Theropod Dinosaurs |last=Stevens |first=K. A. |date=April 1, 2011 |access-date=July 19, 2013 |archive-date=August 19, 2018 |archive-url=https://web.archive.org/web/20180819050655/http://ix.cs.uoregon.edu/~kent/paleontology/binocularVision/ |url-status=live }}</ref>

Thomas Holtz Jr. would note that high depth perception of ''Tyrannosaurus'' may have been due to the prey it had to hunt, noting that it had to hunt ceratopsians such as ''[[Triceratops]]'', ankylosaurs such as ''[[Ankylosaurus]]'', and hadrosaurs. He would suggest that this made precision more crucial for ''Tyrannosaurus'' enabling it to, "get in, get that blow in and take it down." In contrast, ''[[Acrocanthosaurus]]'' had limited depth perception because they hunted large sauropods, which were relatively rare during the time of ''Tyrannosaurus''.<ref name="HoltzLecture2013" />

Though no ''Tyrannosaurus'' [[Scleral Ring|sclerotic ring]] has been found, [[Kenneth Carpenter]] estimated its size based on that of ''Gorgosaurus''. The inferred sclerotic ring for the [[Stan (dinosaur)|Stan specimen]] is ~{{convert|7|cm|in|abbr=on|sp=us}} in diameter with an internal aperture diameter of ~{{convert|3.5|cm|in|abbr=on|sp=us}}. Based on eye proportions in living reptiles, this implies a pupil diameter of about {{convert|2.5|cm|in|abbr=on|sp=us}}, an iris diameter about that of the sclerotic ring, and an eyeball diameter of {{convert|11-12|cm|in|abbr=on|sp=us}}. Carpenter also estimated an eyeball depth of ~{{convert|7.7-9.6|cm|in|abbr=on|sp=us}}. Based on these calculations, the [[f-number]] for Stan's eye is 3–3.8; since [[Diurnality|diurnal]] animals have f-numbers of 2.1 or higher, this would indicate that ''Tyrannosaurus'' had poor low-light vision and hunted during the day.<ref name="Trexpaleobiologychapter14">{{cite book|author=Carpenter, K.|chapter=A Closer Look at the Scavenging versus Predation by ''Tyrannosaurus rex''|title=Tyrannosaurid Paleobiology |year=2013 |publisher=Indiana University Press |isbn=978-0-253-00930-2 |editor-last=Parrish |editor-first=M. J. |editor-last2=Molnar |editor-first2=R. E. |editor-last3=Currie |editor-first3=P. J. |editor-last4=Koppelhus |editor-first4=E. B. |series=Life of the Past |location=Bloomington (Ind.) |pages=265–278 }}</ref>

''Tyrannosaurus'' had very large [[olfactory bulb]]s and [[olfactory nerve]]s relative to their brain size, the organs responsible for a heightened sense of smell. This suggests that the sense of smell was highly developed, and implies that tyrannosaurs could detect carcasses by scent alone across great distances. The sense of smell in tyrannosaurs may have been comparable to modern [[vulture]]s, which use scent to track carcasses for scavenging. Research on the olfactory bulbs has shown that ''T. rex'' had the most highly developed sense of smell of 21 sampled non-avian dinosaur species.<ref name="Calgary Herald">{{cite news |url=http://www.canada.com/calgaryherald/story.html?id=3641f27e-ca2e-44e8-a56b-f9a0b4aef4b5 |title=''T. Rex'' brain study reveals a refined 'nose' |date=October 28, 2008 |newspaper=Calgary Herald |access-date=October 29, 2008 |archive-date=December 6, 2008 |archive-url=https://web.archive.org/web/20081206065850/http://www.canada.com/calgaryherald/story.html?id=3641f27e-ca2e-44e8-a56b-f9a0b4aef4b5 |url-status=live }}</ref>
[[File:Tyrannosaurus brain aus.jpg|thumb|Cast of the braincase at the [[Australian Museum]], Sydney]]
Somewhat unusually among theropods, ''T.&nbsp;rex'' had a very long [[cochlea]]. The length of the cochlea is often related to hearing acuity, or at least the importance of hearing in behavior, implying that hearing was a particularly important sense to tyrannosaurs. Specifically, data suggests that ''T. rex'' heard best in the low-frequency range, and that low-frequency sounds were an important part of tyrannosaur behavior.<ref name="witmer2009" /> A 2017 study by Thomas Carr and colleagues found that the snout of tyrannosaurids was highly sensitive, based on a high number of small openings in the facial bones of the related ''Daspletosaurus'' that contained [[sensory neuron]]s. The study speculated that tyrannosaurs might have used their sensitive snouts to measure the temperature of their nests and to gently pick up eggs and hatchlings, as seen in modern crocodilians.<ref name="carr2017" /> 
Another study published in 2021 further suggests that ''Tyrannosaurus'' had an acute sense of touch, based on neurovascular canals in the front of its jaws, which it could utilize to better detect and consume prey. The study, published by Kawabe and Hittori et al., suggests that ''Tyrannosaurus'' could also accurately sense slight differences in material and movement, allowing it to utilize different feeding strategies on different parts of its prey's carcasses depending on the situation. The sensitive neurovascular canals of ''Tyrannosaurus'' also likely were adapted to performing fine movements and behaviors such as nest building, parental care, and other social behavior such as intraspecific communication. The results of this study also align with results made in studying the related tyrannosaurid ''[[Daspletosaurus horneri]]'' and the [[allosauroid]] ''[[Neovenator]]'', which have similar neurovascular adaptations, suggesting that the faces of theropods were highly sensitive to pressure and touch.<ref>{{Cite journal|doi=10.1080/08912963.2021.1965137|title=Complex neurovascular system in the dentary of Tyrannosaurus|year=2021|last1=Kawabe|first1=Soichiro|last2=Hattori|first2=Soki|journal=Historical Biology|volume=34 |issue=7 |pages=1137–1145|doi-access=free|bibcode=2022HBio...34.1137K }}</ref><ref>{{Cite web|url=https://phys.org/news/2021-08-rex-jaw-sensors-fearsome-predator.html|title=T. rex's jaw had sensors that made it an even more fearsome predator|website=phys.org|access-date=August 23, 2021|archive-date=August 23, 2021|archive-url=https://web.archive.org/web/20210823232627/https://phys.org/news/2021-08-rex-jaw-sensors-fearsome-predator.html|url-status=live}}</ref> However, a more recent study reviewing the evolution of the trigeminal canals among sauropsids notes that a much denser network of neurovascular canals in the snout and lower jaw is more commonly encountered in aquatic or semiaquatic taxa (e.g., ''[[Spinosaurus]]'', ''[[Halszkaraptor]]'', ''[[Plesiosaurus]]''), and taxa that developed a rhamphotheca (e.g., ''[[Caenagnathasia]]''), while the network of canals in ''Tyrannosaurus'' appears simpler, though still more derived than in most ornithischians, and overall  
terrestrial taxa such as tyrannosaurids and ''Neovenator'' may have had average facial sensitivity for non-edentulous terrestrial theropods, although further research is needed. The neurovascular canals in ''Tyrannosaurus'' may instead have supported soft tissue structures for thermoregulation or social signaling, the latter of which could be confirmed by the fact that the neurovascular network of canals may have changed during ontogeny.<ref>{{Cite journal|last=Benoit|first=Florian Bouabdellah, Emily Lessner, and Julien|date=January 20, 2022|title=The rostral neurovascular system of Tyrannosaurus rex|url=https://palaeo-electronica.org/content/2022/3518-t-rex-trigeminal-canals|journal=Palaeontologia Electronica|language=English|volume=25|issue=1|pages=1–20|doi=10.26879/1178|s2cid=246204236|issn=1094-8074|doi-access=free|archive-date=March 16, 2022|access-date=January 22, 2022|archive-url=https://web.archive.org/web/20220316214524/https://palaeo-electronica.org/content/2022/3518-t-rex-trigeminal-canals|url-status=live}}</ref>

A study by Grant R. Hurlburt, Ryan C. Ridgely and Lawrence Witmer obtained estimates for [[Encephalization Quotient]]s (EQs), based on reptiles and birds, as well as estimates for the ratio of cerebrum to brain mass. The study concluded that ''Tyrannosaurus'' had the relatively largest brain of all adult non-avian dinosaurs with the exception of certain small maniraptoriforms (''[[Bambiraptor]]'', ''[[Troodon]]'' and ''[[Ornithomimus]]''). The study found that ''Tyrannosaurus'''s relative brain size was still within the range of modern reptiles, being at most 2 [[standard deviations]] above the mean of non-avian reptile EQs. The estimates for the ratio of cerebrum mass to brain mass would range from 47.5 to 49.53 percent. According to the study, this is more than the lowest estimates for extant birds (44.6 percent), but still close to the typical ratios of the smallest sexually mature alligators which range from 45.9–47.9 percent.<ref name="Trexpaleobiologychapter6">{{Cite book |title=Tyrannosaurid Paleobiology |last1=Hurlburt |first1=G. S. |last2=Ridgely |first2=R. C. |last3=Witmer |first3=L. M. |date=July 5, 2013 |publisher=Indiana University Press |isbn=978-0-253-00947-0 |pages=134–154 |chapter=Relative size of brain and cerebrum in Tyrannosaurid dinosaurs: an analysis using brain-endocast quantitative relationships in extant alligators |access-date=October 20, 2013 |editor-last=Parrish |editor-first=M. J. |editor-last2=Molnar |editor-first2=R. E. |editor-last3=Currie |editor-first3=P. J. |editor-last4=Koppelhus |editor-first4=E. B. |chapter-url=https://www.researchgate.net/publication/256536375}}</ref> Other studies, such as those by Steve Brusatte, indicate the encephalization quotient of ''Tyrannosaurus'' was similar in range (2.0–2.4) to a [[chimpanzee]] (2.2–2.5), though this may be debatable as reptilian and mammalian encephalization quotients are not equivalent.<ref>{{cite book|last=Brusatten|first=Steve|title=The Rise and Fall of the Dinosaurs|date=2018|publisher=HarperCollins Publishers|location=New York, New York|isbn=978-0-06-249043-8|page=219}}</ref>

=== Social behavior ===
[[File:Tyrannosaurus Growth Series LACM.jpg|left|thumb|Mounted skeletons of different age groups (skeleton in lower left based on ''[[Stygivenator]]''), [[Natural History Museum of Los Angeles County]]]]
[[Philip J. Currie]] suggested that Tyrannosaurus may have been [[pack hunter]]s, comparing ''T. rex'' to related species ''[[Tarbosaurus bataar]]'' and ''[[Albertosaurus sarcophagus]]'', citing fossil evidence that may indicate [[Sociality|gregarious]] (describing animals that travel in herds or packs) behavior.<ref name="discoverdinogangs">{{cite web|date=June 22, 2011|title=Dino Gangs|url=http://www.discoveryuk.com/the-loop/dino-gangs/|archive-url=https://web.archive.org/web/20120119125039/http://www.discoveryuk.com/the-loop/dino-gangs/|archive-date=January 19, 2012|access-date=January 19, 2012|website=Discovery Channel}}</ref> A find in [[South Dakota]] where three ''T. rex'' skeletons were in close proximity may suggest the formation of a pack.<ref name="tgraphpack">{{Cite news|last=Collins|first=N.|date=June 22, 2011|title=Tyrannosaurus Rex 'hunted in packs'|work=The Telegraph|url=https://www.telegraph.co.uk/news/science/dinosaurs/8589113/Tyrannosaurus-Rex-hunted-in-packs.html |archive-url=https://ghostarchive.org/archive/20220110/https://www.telegraph.co.uk/news/science/dinosaurs/8589113/Tyrannosaurus-Rex-hunted-in-packs.html |archive-date=January 10, 2022 |url-access=subscription |url-status=live|access-date=March 23, 2014}}{{cbignore}}</ref><ref name="djournal">{{Cite web|last=Wallis|first=P.|date=June 11, 2012|title=Op-Ed: T. Rex pack hunters? Scary, but likely to be true|url=http://digitaljournal.com/article/326451|access-date=December 23, 2015|website=Digitaljournal.com|archive-date=April 16, 2021|archive-url=https://web.archive.org/web/20210416141803/http://www.digitaljournal.com/article/326451|url-status=live}}</ref> Cooperative pack hunting may have been an effective strategy for subduing prey with advanced [[anti-predator adaptation]]s which pose potential lethality such as ''[[Triceratops]]'' and ''[[Ankylosaurus]]''.<ref name="discoverdinogangs" />

Currie's pack-hunting ''T. rex'' hypothesis has been criticized for not having been [[peer-review]]ed, but rather was discussed in a television interview and book called ''Dino Gangs''.<ref name="switek2011dinogangs">{{Cite web|last=Switek|first=B.|date=July 25, 2011|title=A bunch of bones doesn't make a gang of bloodthirsty tyrannosaurs|url=https://www.theguardian.com/science/blog/2011/jul/25/bunch-bones-gang-bloodthirsty-tyrannosaurs|access-date=June 21, 2015|website=The Guardian|archive-date=December 21, 2018|archive-url=https://web.archive.org/web/20181221011020/https://www.theguardian.com/science/blog/2011/jul/25/bunch-bones-gang-bloodthirsty-tyrannosaurs|url-status=live}}</ref> The Currie theory for pack hunting by ''T. rex'' is based mainly by analogy to a different species, ''Tarbosaurus bataar''. Evidence of gregariousness in ''T. bataar'' itself has not been peer-reviewed, and to Currie's own admission, can only be interpreted with reference to evidence in other closely related species. According to Currie gregariousness in ''Albertosaurus sarcophagus'' is supported by the discovery of 26 individuals with varied ages in the Dry Island bonebed. He ruled out the possibility of a predator trap due to the similar preservation state of individuals and the near absence of herbivores.<ref name="switek2011dinogangs" /><ref name="currie1998">{{cite journal|last=Currie|first=Philip J.|author-link=Philip J. Currie|year=1998|title=Possible evidence of gregarious behaviour in tyrannosaurids|url=http://www.mnhn.ul.pt/geologia/gaia/21.pdf|journal=Gaia|volume=15|pages=271–277|archive-url=https://web.archive.org/web/20090326062833/http://www.mnhn.ul.pt/geologia/gaia/21.pdf|archive-date=March 26, 2009|access-date=May 3, 2009}} (not printed until 2000)</ref>

Additional support of tyrannosaurid gregariousness can be found in fossilized [[trackway]]s from the Upper Cretaceous [[Wapiti Formation]] of northeastern [[British Columbia]], Canada, left by three tyrannosaurids traveling in the same direction.<ref name="TG-20140724">{{Cite web|last=Sample|first=I.|date=July 23, 2014|title=Researchers find first sign that tyrannosaurs hunted in packs|url=https://www.theguardian.com/science/2014/jul/23/tyrannosaurs-hunted-packs-tracks-canada|access-date=July 28, 2014|website=[[The Guardian]]|archive-date=December 15, 2018|archive-url=https://web.archive.org/web/20181215141823/https://www.theguardian.com/science/2014/jul/23/tyrannosaurs-hunted-packs-tracks-canada|url-status=live}}</ref><ref>{{Cite journal|last=McCrea|first=R. T.|year=2014|title=A 'Terror of Tyrannosaurs': The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae|journal=PLOS ONE|volume=9|issue=7|article-number=e103613|bibcode=2014PLoSO...9j3613M|doi=10.1371/journal.pone.0103613|pmc=4108409|pmid=25054328|doi-access=free}}</ref> According to scientists assessing the Dino Gangs program, the evidence for pack hunting in ''Tarbosaurus'' and ''Albertosaurus'' is weak and based on group skeletal remains for which alternate explanations may apply (such as drought or a flood forcing dinosaurs to die together in one place).<ref name="switek2011dinogangs" /> Others researchers have speculated that instead of large theropod social groups, some of these finds represent behavior more akin to [[Komodo dragon]]-like mobbing of carcasses, even going as far as to say true pack-hunting behavior may not exist in any non-avian dinosaurs due to its rarity in modern predators.<ref name="roachbrinkman2007">{{cite journal|last=Roach|first=Brian T.|author2=Brinkman, Daniel T.|year=2007|title=A reevaluation of cooperative pack hunting and gregariousness in ''Deinonychus antirrhopus'' and other nonavian theropod dinosaurs|journal=Bulletin of the Peabody Museum of Natural History|volume=48|issue=1|pages=103–138|doi=10.3374/0079-032X(2007)48[103:AROCPH]2.0.CO;2|s2cid=84175628 }}</ref> Pathologies of ''Tyrannosaurus'' specimens have been suggested as evidence of conspecific attack, including "Wyrex" with a hole penetrating its jugual and severe trauma on its tail that shows signs of [[bone remodeling]] (not regrowth).<ref name="Trexpaleobiologychapter10">{{cite book|author=Rothschild, B.M.|chapter=Clawing Their Way to the Top: Tyrannosaurid Pathology and Lifestyle|title=Tyrannosaurid Paleobiology |year=2013 |publisher=Indiana University Press |isbn=978-0-253-00930-2 |editor-last=Parrish |editor-first=M. J. |editor-last2=Molnar |editor-first2=R. E. |editor-last3=Currie |editor-first3=P. J. |editor-last4=Koppelhus |editor-first4=E. B. |series=Life of the Past |location=Bloomington (Ind.) |pages=211–222 }}</ref><ref>{{cite journal|author1=Anné, J.|author2=Whitney, M.|author3=Brocklehurst, R.|author4=Donnelly, K.|author5=Rothschild, B.|year=2023|title=Unusual lesions seen in the caudals of the hadrosaur, ''Edmontosaurus annectens''|journal=The Anatomical Record|volume=306|issue=3|pages=594–606|doi=10.1002/ar.25078|pmid=36089756 }}</ref>

===Diet and feeding behavior===
{{Main|Feeding behavior of Tyrannosaurus|l1 = Feeding behavior of ''Tyrannosaurus''}}

{{multiple image
|align = right
| direction = horizontal
|perrow=2/1
|total_width = 350

|image1 = Tyrannosaurus tooth marks.png
| alt1 =
|image2 = Tyrannosaurus cannibalism evidence.png
| alt2 =

|footer = ''Tyrannosaurus'' tooth marks on bones of various herbivorous dinosaurs (left) as well as other ''Tyrannosaurus'' (right)
}}

Most paleontologists accept that ''Tyrannosaurus'' was both an active [[predator]] and a [[scavenger]] like most large [[carnivores]].<ref name="nationalgeographic">{{cite magazine |url=https://www.nationalgeographic.com/science/phenomena/2013/07/16/time-to-slay-the-t-rex-scavenger-debate/ |title=Time to Slay the ''T. rex'' Scavenger "Debate" |date=July 16, 2013 |magazine=National Geographic |archive-url=https://web.archive.org/web/20180712030717/https://www.nationalgeographic.com/science/phenomena/2013/07/16/time-to-slay-the-t-rex-scavenger-debate/ |archive-date=July 12, 2018 }}</ref> By far the largest carnivore in its environment, ''T. rex'' was most likely an [[apex predator]], preying upon [[hadrosaur]]s, armored herbivores like [[ceratopsia]]ns and [[ankylosaur]]s, and possibly [[sauropod]]s.<ref>{{Cite journal |url=https://www.smithsonianmag.com/science-nature/when-tyrannosaurus-chomped-sauropods-67170161/ |title=When ''Tyrannosaurus'' Chomped Sauropods |last=Black |first=Riley |date=April 13, 2012 |publisher=Smithsonian Media |access-date=August 24, 2013 |journal=Smithsonian Magazine |volume=25 |page=469 |doi=10.1671/0272-4634(2005)025[0469:TRFTUC]2.0.CO;2 |s2cid=131583311 |archive-date=April 12, 2019 |archive-url=https://web.archive.org/web/20190412174912/https://www.smithsonianmag.com/science-nature/when-tyrannosaurus-chomped-sauropods-67170161/ |url-status=live |url-access=subscription }}</ref> Enamel δ<sup>44/42</sup>Ca values also suggest the possibility that ''T. rex'' occasionally fed on carcasses of marine reptiles and fish washed up on the shores of the Western Interior Seaway.<ref>{{Cite journal |last1=Martin |first1=Jeremy E. |last2=Hassler |first2=Auguste |last3=Montagnac |first3=Gilles |last4=Therrien |first4=François |last5=Balter |first5=Vincent |date=February 10, 2022 |title=The stability of dinosaur communities before the Cretaceous–Paleogene (K–Pg) boundary: A perspective from southern Alberta using calcium isotopes as a dietary proxy |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article/134/9-10/2548/611716/The-stability-of-dinosaur-communities-before-the |journal=[[Geological Society of America Bulletin]] |language=en |volume=134 |issue=9–10 |pages=2548–2560 |doi=10.1130/B36222.1 |bibcode=2022GSAB..134.2548M |issn=0016-7606 |access-date=November 18, 2024 |via=GeoScienceWorld |hdl=2164/20498 |hdl-access=free |archive-date=October 12, 2024 |archive-url=https://web.archive.org/web/20241012034919/https://pubs.geoscienceworld.org/gsa/gsabulletin/article/134/9-10/2548/611716/The-stability-of-dinosaur-communities-before-the |url-status=live }}</ref> A study in 2012 by Karl Bates and Peter Falkingham found that ''Tyrannosaurus'' had the most powerful bite of any terrestrial animal that has ever lived, finding an adult ''Tyrannosaurus'' could have exerted 35,000 to 57,000 [[Newton (unit)|N]] (7,868 to 12,814 [[Pound (force)|lbf]]) of force in the back teeth.<ref>{{Cite web |url=https://www.smithsonianmag.com/science-nature/the-tyrannosaurus-rexs-dangerous-and-deadly-bite-37252918/ |title=The ''Tyrannosaurus rex''s Dangerous and Deadly Bite |last=Black |first=Riley |date=2012 |website=Smithsonian Magazine |publisher=Smithsonian Institution |access-date=December 20, 2019 |archive-date=May 13, 2014 |archive-url=https://web.archive.org/web/20140513065820/https://www.smithsonianmag.com/science-nature/the-tyrannosaurus-rexs-dangerous-and-deadly-bite-37252918/ |url-status=live }}</ref><ref name="BatesFalkingham2012">{{Cite journal |last1=Bates |first1=K. T. |last2=Falkingham |first2=P. L. |date=February 29, 2012 |title=Estimating maximum bite performance in ''Tyrannosaurus rex'' using multi-body dynamics |journal=Biology Letters |volume=8 |issue=4 |pages=660–664 |doi=10.1098/rsbl.2012.0056 |pmc=3391458 |pmid=22378742 }}</ref><ref>{{Cite book |title=Oxford Handbook of Applied Dental Sciences |last=Scully |first=C. |publisher=Oxford University Press |year=2002 |isbn=978-0-19-851096-3 |page=[https://archive.org/details/oxfordhandbookof00cris/page/156 156] |url=https://archive.org/details/oxfordhandbookof00cris |url-access=registration }}</ref> Even higher estimates were made by Mason B. Meers in 2003.<ref name="MM03" /> This allowed it to crush bones during repetitive biting and fully consume the carcasses of large dinosaurs.<ref name="gignac" /> Stephan Lautenschlager and colleagues calculated that ''Tyrannosaurus'' was capable of a maximum jaw gape of around 80 degrees, a necessary adaptation for a wide range of jaw angles to power the creature's strong bite.<ref>{{Cite journal |title=Estimating cranial musculoskeletal constraints in theropod dinosaurs |date=November 4, 2015 |journal=Royal Society Open Science |volume=2 |issue=11 |article-number=150495 |doi=10.1098/rsos.150495 |pmid=26716007 |pmc=4680622 |last1=Lautenschlager |first1=Stephan |bibcode=2015RSOS....250495L }}</ref><ref>{{Cite web |url=https://www.sciencedaily.com/releases/2015/11/151103213705.htm |title=The better to eat you with? How dinosaurs' jaws influenced diet |date=November 3, 2015 |website=Science Daily |archive-url=https://web.archive.org/web/20151104162130/https://www.sciencedaily.com/releases/2015/11/151103213705.htm |archive-date=November 4, 2015 |access-date=September 14, 2018}}</ref>

A debate exists, however, about whether ''Tyrannosaurus'' was primarily a [[predation|predator]] or a pure [[scavenger]]. The debate originated in a 1917 study by Lambe which argued that large theropods were pure scavengers because ''Gorgosaurus'' teeth showed hardly any wear.<ref name="Lambe1917Gorgosaurus">{{Cite journal |last=Lambe |first=L. B. |year=1917 |title=The Cretaceous theropodous dinosaur ''Gorgosaurus'' |journal=Memoirs of the Geological Survey of Canada |volume=100 |pages=1–84 |doi=10.4095/101672 |url=https://www.biodiversitylibrary.org/item/252624 |doi-access=free |archive-date=September 9, 2021 |access-date=August 11, 2021 |archive-url=https://web.archive.org/web/20210909121735/https://www.biodiversitylibrary.org/item/252624 |url-status=live }}</ref> This argument disregarded the fact that theropods replaced their teeth quite rapidly. Ever since the first discovery of ''Tyrannosaurus'' most scientists have speculated that it was a predator; like modern large predators it would readily scavenge or steal another predator's kill if it had the opportunity.<ref name="FarlowHoltz2002FossilRecordPredation">{{Cite book |title=The Fossil Record of Predation |last1=Farlow |first1=J. O. |last2=Holtz |publisher=T. R. Jr. |year=2002 |editor-last=Kowalewski |editor-first=M. |series=The Paleontological Society Papers |volume=8 |pages=251–266 |chapter=The fossil record of predation in dinosaurs |editor-last2=Kelley |editor-first2=P. H. |chapter-url=http://www.yale.edu/ypmip/predation/Chapter_09.pdf |archive-url=https://web.archive.org/web/20081031093048/http://www.yale.edu/ypmip/predation/Chapter_09.pdf |archive-date=October 31, 2008 }}</ref>

Paleontologist [[Jack Horner (paleontologist)|Jack Horner]] has been a major proponent of the view that ''Tyrannosaurus'' was not a predator at all but instead was exclusively a scavenger.<ref name="hornerlessem1993" /><ref name="Horner1994SteakKnives">{{Cite journal |last=Horner |first=J. R. |year=1994 |title=Steak knives, beady eyes, and tiny little arms (a portrait of ''Tyrannosaurus'' as a scavenger) |journal=The Paleontological Society Special Publication |volume=7 |pages=157–164|doi=10.1017/S2475262200009497 }}</ref><ref name="BBC2003TrexOnTrial">{{cite news |url=http://news.bbc.co.uk/1/hi/sci/tech/3112527.stm |title=Science/Nature: ''T. rex'' goes on trial |last=Amos |first=J. |date=July 31, 2003 |work=BBC News |access-date=December 23, 2015 |archive-date=March 13, 2012 |archive-url=https://web.archive.org/web/20120313130020/http://news.bbc.co.uk/1/hi/sci/tech/3112527.stm |url-status=live }}</ref> He has put forward arguments in the popular literature to support the pure scavenger hypothesis:

[[File:Tyrannosaurus and Triceratops at Natural History Museum of Los Angeles County.jpg|left|thumb|A ''Tyrannosaurus'' mounted next to a ''[[Triceratops]]'' at the [[Los Angeles Natural History Museum]]]]
* Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey.<ref name="BBC2003TrexOnTrial2">{{cite news|last=Amos|first=J.|date=July 31, 2003|title=Science/Nature: ''T. rex'' goes on trial|work=BBC News|url=http://news.bbc.co.uk/1/hi/sci/tech/3112527.stm|access-date=December 23, 2015|archive-date=March 13, 2012|archive-url=https://web.archive.org/web/20120313130020/http://news.bbc.co.uk/1/hi/sci/tech/3112527.stm|url-status=live}}</ref> Other paleontologists such as [[Thomas R. Holtz Jr.|Thomas Holtz Jr.]] argued that there are plenty of modern-day predators that do not use their forelimbs to hunt such as [[Wolf|wolves]], [[hyena]]s, and [[Secretarybird|secretary birds]] as well as other extinct animals thought to be predators that would not have used their forelimbs such as [[Phorusrhacidae|phorusrhacids]].<ref name="FarlowHoltz2002FossilRecordPredation2">{{Cite journal|last1=Farlow|first1=J. O.|last2=Holtz|first2=T.R.|year=2002|editor-last=Kowalewski|editor-first=M.|editor2-last=Kelley|editor2-first=P. H.|title=The Fossil Record of Predation in Dinosaurs|url=http://www.yale.edu/ypmip/predation/Chapter_09.pdf|journal=The Paleontological Society Papers|volume=8|pages=251–266|doi=10.1017/S108933260000111X|archive-url=https://web.archive.org/web/20081031093048/http://www.yale.edu/ypmip/predation/Chapter_09.pdf|archive-date=October 31, 2008}}</ref><ref name="Tyrantkingbook">{{cite book|last1=Holtz|first1=Thomas R.|title=Tyrannosaurus rex: The Tyrant King|publisher=Book Publishers|year=2008|isbn=978-0-253-35087-9|editor-last1=Larson|editor-first1=Peter|pages=371–394|chapter=Chapter 20: A critical re-appraisal of the obligate scavenging hypothesis for Tyrannosaurus rex and other tyrant dinosaurs|editor-last2=Carpenter|editor-first2=Kenneth|chapter-url=https://www.academia.edu/293223|archive-date=November 15, 2021|access-date=November 15, 2021|archive-url=https://web.archive.org/web/20211115021956/https://www.academia.edu/293223|url-status=live}}</ref>
* Tyrannosaurs had large [[olfactory bulb]]s and [[olfactory nerve]]s (relative to their brain size). These suggest a highly developed sense of smell which could sniff out carcasses over great distances, as modern [[vulture]]s do. Research on the olfactory bulbs of dinosaurs has shown that ''Tyrannosaurus'' had the most highly developed sense of smell of 21 sampled dinosaurs.<ref name="Calgary Herald" />
* Tyrannosaur teeth could crush bone, and therefore could extract as much food ([[bone marrow]]) as possible from carcass remnants, usually the least nutritious parts. Karen Chin and colleagues have found bone fragments in [[coprolite]]s (fossilized feces) that they attribute to tyrannosaurs, but point out that a tyrannosaur's teeth were not well adapted to systematically chewing bone like [[hyena]]s do to extract marrow.<ref name="ChinEtal1998KingSizeCoprolite">{{Cite journal |last1=Chin |first1=K. |last2=Tokaryk |first2=T. T. |last3=Erickson |first3=G. M. |last4=Calk |first4=L. C. |s2cid=4343329 |date=June 18, 1998 |title=A king-sized theropod coprolite |journal=Nature |volume=393 |issue=6686 |pages=680–682 |bibcode=1998Natur.393..680C |doi=10.1038/31461 |url=https://zenodo.org/record/3943146 |archive-date=October 3, 2020 |access-date=August 12, 2020 |archive-url=https://web.archive.org/web/20201003143612/https://zenodo.org/record/3943146 |url-status=live }} Summary at {{cite journal |last=Monastersky |first=R. |date=June 20, 1998 |title=Getting the scoop from the poop of ''T. rex'' |journal=Science News |doi=10.2307/4010364 |jstor=4010364 |volume=153 |issue=25 |page=391 |url=http://www.sciencenews.org/pages/sn_arc98/6_20_98/fob2.htm |archive-url=https://web.archive.org/web/20130511121022/http://www.sciencenews.org/pages/sn_arc98/6_20_98/fob2.htm |archive-date=May 11, 2013 |url-access=subscription }}</ref>
* Since at least some of ''Tyrannosaurus''{{'}}s potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger.<ref name="Horner1994SteakKnives" /> On the other hand, recent analyses suggest that ''Tyrannosaurus'', while slower than large modern terrestrial predators, may well have been fast enough to prey on large [[hadrosaurs]] and [[ceratopsians]].<ref name="HutchinsonGarcia2002TrexSlow" /><ref name="manningetal2008" />

Other evidence suggests hunting behavior in ''Tyrannosaurus''. The eye sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them [[binocular vision]] slightly better than that of modern [[hawk]]s. It is not obvious why [[natural selection]] would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced [[depth perception]] that [[stereoscopic vision]] provides.<ref name="Stevens2006Binocular" /><ref name="jaffe" /> In modern animals, binocular vision is found mainly in predators.

[[File:DMNS Edmontosaurus.png|thumb|right|The damage to the tail vertebrae of this ''Edmontosaurus annectens'' skeleton (on display at the Denver Museum of Nature and Science) indicates that it may have been bitten by a ''Tyrannosaurus'']]
A skeleton of the hadrosaurid ''[[Edmontosaurus]] annectens'' has been described from Montana with healed tyrannosaur-inflicted damage on its tail [[vertebra]]e. The fact that the damage seems to have healed suggests that the ''Edmontosaurus'' survived a tyrannosaur's attack on a living target, i.e. the tyrannosaur had attempted active predation.<ref name="carpenter1998">{{Cite journal |last=Carpenter |first=K. |author-link=Kenneth Carpenter |year=1998 |title=Evidence of predatory behavior by theropod dinosaurs |url=http://vertpaleo.org/publications/jvp/15-576-591.cfm |journal=Gaia |volume=15 |pages=135–144 |archive-url=https://web.archive.org/web/20071117132451/http://vertpaleo.org/publications/jvp/15-576-591.cfm <!--Added by H3llBot--> |archive-date=November 17, 2007 |access-date=December 5, 2007}}</ref> Despite the consensus that the tail bites were caused by ''Tyrannosaurus'', there has been some evidence to show that they might have been created by other factors. For example, a 2014 study suggested that the tail injuries might have been due to ''Edmontosaurus'' individuals stepping on each other,<ref>{{cite book|title=Hadrosaurs|chapter=Paleopathology in Late Cretaceous Hadrosauridae from Alberta, Canada |date=2015|pages=540–571|publisher=Indiana University Press|isbn=978-0-253-01390-3|editor1=Eberth, David A.|editor2=Evans, David C.}} [https://www.researchgate.net/publication/290310286_Paleopathology_in_Late_Cretaceous_Hadrosauridae_from_Alberta_Canada preprint] {{Webarchive|url=https://web.archive.org/web/20200703105409/https://www.researchgate.net/publication/290310286_Paleopathology_in_Late_Cretaceous_Hadrosauridae_from_Alberta_Canada |date=July 3, 2020 }}</ref> while another study in 2020 backs up the hypothesis that biomechanical stress is the cause for the tail injuries.<ref>{{cite journal |journal=PALAIOS |date=2020 |volume=35 |issue=4 |doi=10.2110/palo.2019.079 |url=https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/35/4/201/584648/SKELETAL-TRAUMA-WITH-IMPLICATIONS-FOR-INTRATAIL?redirectedFrom=fulltext-- |title=Skeletal Trauma with Implications for Intratail Mobility in Edmontosaurus Annectens from a Monodominant Bonebed, Lance Formation (Maastrichtian), Wyoming USA |last1=Siviero |first1=ART V. |last2=Brand |first2=Leonard R. |last3=Cooper |first3=Allen M. |last4=Hayes |first4=William K. |last5=Rega |first5=Elizabeth |last6=Siviero |first6=Bethania C.T. |s2cid=218503493 |pages=201–214 |bibcode=2020Palai..35..201S |archive-date=July 4, 2020 |access-date=July 2, 2020 |archive-url=https://web.archive.org/web/20200704084853/https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/35/4/201/584648/SKELETAL-TRAUMA-WITH-IMPLICATIONS-FOR-INTRATAIL?redirectedFrom=fulltext-- |url-status=live |url-access=subscription }}</ref> There is also evidence for an aggressive interaction between a ''[[Triceratops]]'' and a ''Tyrannosaurus'' in the form of partially healed tyrannosaur tooth marks on a ''Triceratops'' brow horn and [[squamosal]] (a bone of the [[neck frill]]); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor.<ref name="JH08">{{Cite book |title=Tyrannosaurus rex, the Tyrant King (Life of the Past) |last1=Happ |first1=J. |last2=Carpenter |first2=K. |publisher=Indiana University Press |year=2008 |isbn=978-0-253-35087-9 |editor-last=Carpenter |editor-first=K. |location=Bloomington |pages=355–368 |chapter=An analysis of predator–prey behavior in a head-to-head encounter between ''Tyrannosaurus rex'' and ''Triceratops'' |editor-last2=Larson |editor-first2=P. E.}}</ref> Since the ''Triceratops'' wounds healed, it is most likely that the ''Triceratops'' survived the encounter and managed to overcome the ''Tyrannosaurus''. In a battle against a bull ''Triceratops'', the ''Triceratops'' would likely defend itself by inflicting fatal wounds to the ''Tyrannosaurus'' using its sharp horns.<ref>{{Cite book |title=The Horned Dinosaurs |year=1996 |url=https://archive.org/details/horneddinosaursn00dods |url-access=limited |last=Dodson |first=P. |publisher=Princeton University Press |page=[https://archive.org/details/horneddinosaursn00dods/page/n32 19]}}</ref> Studies of [[Sue (dinosaur)|Sue]] found a broken and healed [[fibula]] and tail vertebrae, scarred facial bones and a tooth from another ''Tyrannosaurus'' embedded in a neck vertebra, providing evidence for aggressive behavior.<ref name="TC98">{{Cite journal |last1=Tanke |first1=D. H. |last2=Currie |first2=P. J. |year=1998 |title=Head-biting behavior in theropod dinosaurs: paleopathological evidence |url=http://www.mnhn.ul.pt/geologia/gaia/12.pdf  |journal=Gaia |issue=15 |pages=167–184 |issn=0871-5424 |archive-url=https://web.archive.org/web/20080227134632/http://www.mnhn.ul.pt/geologia/gaia/12.pdf |archive-date=February 27, 2008 |author-link=Darren Tanke}}</ref> Studies on hadrosaur vertebrae from the Hell Creek Formation that were punctured by the teeth of what appears to be a late-stage juvenile ''Tyrannosaurus'' indicate that despite lacking the bone-crushing adaptations of the adults, young individuals were still capable of using the same bone-puncturing feeding technique as their adult counterparts.<ref name="Peterson">{{Cite journal |last1=Peterson |first1=J. E. |last2=Daus |first2=K. N. |date=March 4, 2019 |title=Feeding traces attributable to juvenile ''Tyrannosaurus rex'' offer insight into ontogenetic dietary trends |journal=PeerJ |volume=7 |article-number=e6573 |doi=10.7717/peerj.6573 |issn=2167-8359 |pmid=30863686|pmc=6404657 |doi-access=free }}</ref>

''Tyrannosaurus'' may have had infectious [[saliva]] used to kill its prey, as proposed by [[William Abler]] in 1992. Abler observed that the {{Dinogloss|serrations}} (tiny protuberances) on the cutting edges of the teeth are closely spaced, enclosing little chambers. These chambers might have trapped pieces of carcass with bacteria, giving ''Tyrannosaurus'' a deadly, infectious bite much like the [[Komodo dragon]] was thought to have.<ref name="abler1992">{{Cite journal |last=Abler |first=W. L. |date=1992 |title=The serrated teeth of tyrannosaurid dinosaurs, and biting structures in other animals |journal=Paleobiology |volume=18 |issue=2 |pages=161–183 |doi=10.1017/S0094837300013956|bibcode=1992Pbio...18..161A |s2cid=88238481 }}</ref><ref name="goldstein2013">{{Cite journal |last1=Goldstein |first1=E. J. C. |last2=Tyrrell |first2=K. L. |last3=Citron |first3=D. M. |last4=Cox |first4=C. R. |last5=Recchio |first5=I. M. |last6=Okimoto |first6=B. |last7=Bryja |first7=J. |last8=Fry |first8=B. G. |s2cid=9932073 |date=June 1, 2013 |title=Anaerobic and aerobic bacteriology of the saliva and gingiva from 16 captive Komodo dragons (''Varanus komodoensis''): new implications for the "bacteria as venom" model |journal=Journal of Zoo and Wildlife Medicine |volume=44 |issue=2 |pages=262–272 |doi=10.1638/2012-0022R.1 |pmid=23805543 |issn=1042-7260}}</ref> Jack Horner and Don Lessem, in a 1993 popular book, questioned Abler's hypothesis, arguing that ''Tyrannosaurus''{{'}}s tooth serrations as more like cubes in shape than the serrations on a Komodo monitor's teeth, which are rounded.<ref name="hornerlessem1993" />{{rp|214–215}}

''Tyrannosaurus'', and most other theropods, probably primarily processed carcasses with lateral shakes of the head, like crocodilians. The head was not as maneuverable as the skulls of [[allosauroidea|allosauroids]], due to flat joints of the neck vertebrae.<ref name="ESetal2013">{{Cite journal |last1=Snively |first1=E. |last2=Cotton |first2=J. R. |last3=Ridgely |first3=R. |last4=Witmer |first4=L. M. |year=2013 |title=Multibody dynamics model of head and neck function in ''Allosaurus'' (Dinosauria, Theropoda) |journal=Palaeontologia Electronica |volume=16 |issue=2 |page=338 |doi=10.26879/338|doi-access=free |bibcode=2013PalEl..16..338S }}</ref>

Evidence also strongly suggests that tyrannosaurs were at least occasionally cannibalistic. ''Tyrannosaurus'' itself has strong evidence pointing towards it having been cannibalistic in at least a scavenging capacity based on tooth marks on the foot bones, humerus, and metatarsals of one specimen.<ref name="HornerCurrie_et.al._2010_Trex_cannibalism">{{Cite journal |last1=Longrich |first1=N. R. |last2=Horner |first2=J. R. |last3=Erickson |first3=G. M. |last4=Currie |first4=P. J. |year=2010 |title=Cannibalism in ''Tyrannosaurus rex'' |journal=PLOS ONE |volume=5 |issue=10 |article-number=e13419 |doi=10.1371/journal.pone.0013419 |pmc=2955550 |pmid=20976177|bibcode=2010PLoSO...513419L |doi-access=free }}</ref>

=== Parenting ===
While there is no direct evidence of ''Tyrannosaurus'' raising their young (the rarity of juvenile and nest Tyrannosaur fossils has left researchers guessing), it has been suggested by some that like its closest living relatives, modern archosaurs (birds and crocodiles) ''Tyrannosaurus'' may have protected and fed its young. Crocodilians and birds are often suggested by some paleontologists to be modern analogues for dinosaur parenting.<ref>{{Cite book|last=Farlow|first=James Orville|url=https://books.google.com/books?id=jXU6atz3RTYC&dq=dinosaur+parenting+behavior&pg=PA21|title=Paleobiology of the Dinosaurs|date=1989|publisher=Geological Society of America|isbn=978-0-8137-2238-2|language=en}}</ref> Direct evidence of parental behavior exists in other dinosaurs such as ''[[Maiasaura|Maiasaura peeblesorum]]'', the first dinosaur to have been discovered to raise its young, as well as more closely related [[Oviraptoridae|Oviraptorids]], the latter suggesting parental behavior in theropods.<ref>"Maiasaura," Dodson, et al. (1994); pages 116-117</ref><ref>{{cite journal|last1=Horner|first1=J.R.|last2=Makela|first2=R.|year=1979|title=Nest of juveniles provides evidence of family structure among dinosaurs|journal=Nature|volume=282|issue=5736|pages=296–298|bibcode=1979Natur.282..296H|doi=10.1038/282296a0|s2cid=4370793}}</ref><ref>{{cite web|title="The Best of all Mothers" Maiasaura peeblesorum|url=http://bioweb.uwlax.edu/bio203/s2014/fischbac_sama/interactions.htm|access-date=March 22, 2021|website=bioweb.uwlax.edu/|publisher=University of Wisconsin-La Crosse|archive-date=June 16, 2022|archive-url=https://web.archive.org/web/20220616015020/http://bioweb.uwlax.edu/bio203/s2014/fischbac_sama/interactions.htm|url-status=live}}</ref><ref>{{Cite journal|last1=Norell|first1=Mark A.|last2=Clark|first2=James M.|last3=Chiappe|first3=Luis M.|last4=Dashzeveg|first4=Demberelyin|date=1995|title=A nesting dinosaur|url=https://www.nature.com/articles/378774a0|journal=Nature|language=en|volume=378|issue=6559|pages=774–776|doi=10.1038/378774a0|bibcode=1995Natur.378..774N|s2cid=4245228|issn=1476-4687|url-access=subscription|archive-date=November 2, 2021|access-date=November 15, 2021|archive-url=https://web.archive.org/web/20211102205739/https://www.nature.com/articles/378774a0|url-status=live}}</ref><ref>{{Cite journal|last=Watanabe|first=Myrna E.|date=March 1, 2009|title=Evolving Ideas on the Origins of Parental Care|journal=BioScience|volume=59|issue=3|page=272|doi=10.1525/bio.2009.59.3.17|s2cid=85066992|issn=0006-3568}}</ref>

===Pathology===

{{multiple image
|align = right
| direction = vertical
|perrow=2/1
|total_width = 250

|image1 = Common-Avian-Infection-Plagued-the-Tyrant-Dinosaurs-pone.0007288.g002.jpg
| alt1 =
|image2 = T. rex infection.png
| alt2 =

|footer = Jaw bones (top) and life restoration showing injuries caused by either parasite infections or bites
}}

In 2001, Bruce Rothschild and others published a study examining evidence for [[stress fractures]] and [[tendon avulsions]] in [[theropod]] dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by regular behavior than other types of injuries. Of the 81 ''Tyrannosaurus'' foot bones examined in the study, one was found to have a stress fracture, while none of the 10 hand bones were found to have stress fractures. The researchers found tendon avulsions only among ''Tyrannosaurus'' and ''[[Allosaurus]]''. An avulsion injury left a divot on the humerus of Sue the ''T.&nbsp;rex'', apparently located at the origin of the [[deltoid muscle|deltoid]] or [[teres major]] muscles. The presence of avulsion injuries being limited to the forelimb and shoulder in both ''Tyrannosaurus'' and ''Allosaurus'' suggests that theropods may have had a musculature more complex than and functionally different from those of birds. The researchers concluded that Sue's tendon avulsion was probably obtained from struggling prey. The presence of stress fractures and tendon avulsions, in general, provides evidence for a "very active" predation-based diet rather than obligate scavenging.<ref name="rothschild-dino">{{Cite book |title=Mesozoic Vertebrate Life |last1=Rothschild |first1=B. |last2=Tanke |first2=D. H. |last3=Ford |first3=T. L. |publisher=Indiana University Press |year=2001 |editor-last=Tanke |editor-first=D. H. |pages=331–336 |chapter=Theropod stress fractures and tendon avulsions as a clue to activity |editor-last2=Carpenter |editor-first2=K.}}</ref>

A 2009 study showed that smooth-edged holes in the skulls of several specimens might have been caused by ''[[Trichomonas]]''-like parasites that commonly infect [[bird]]s. According to the study, seriously infected individuals, including "Sue" and MOR 980 ("Peck's Rex"), might therefore have died from starvation after feeding became increasingly difficult. Previously, these holes had been explained by the bacterious bone infection [[Actinomycosis]] or by intraspecific attacks.<ref name="Wolff">{{Cite journal |last1=Wolff |first1=E. D. S. |last2=Salisbury |first2=S. W. |last3=Horner |first3=J. R. |last4=Varricchi |first4=D. J. |year=2009 |editor-last=Hansen |editor-first=D. M. |title=Common Avian Infection Plagued the Tyrant Dinosaurs |journal=PLOS ONE |volume=4 |issue=9 |article-number=e7288 |bibcode=2009PLoSO...4.7288W |doi=10.1371/journal.pone.0007288 |pmc=2748709 |pmid=19789646|doi-access=free }}</ref> A subsequent study found that while trichomoniasis has many attributes of the model proposed (osteolytic, intra oral) several features make the assumption that it was the cause of death less supportable by evidence. For example, the observed sharp margins with little reactive bone shown by the radiographs of ''Trichomonas''-infected birds are dissimilar to the reactive bone seen in the affected ''T. rex'' specimens. Also, trichomoniasis can be very rapidly fatal in birds (14 days or less) albeit in its milder form, and this suggests that if a ''Trichomonas''-like protozoan is the culprit, trichomoniasis was less acute in its non-avian dinosaur form during the Late Cretaceous. Finally, the relative size of this type of lesions is much larger in small bird throats, and may not have been enough to choke a ''T. rex''.<ref>{{Cite book |last=Rega |first=E. |chapter=Disease in Dinosaurs |editor-last1=Brett-Surman |editor-first1=M. |editor-last2=Holtz |editor-first2=T. |editor-last3=Farlow |editor-first3=J. |title=The Complete Dinosaur |publisher=Indiana University Press |location=Bloomington |year=2012}}</ref> A more recent study examining the pathologies concluded that the osseous alteration observed most closely resembles those around healing human cranial trepanations and healing fractures in the Triassic reptile ''[[Stagonolepis]],'' in the absence of infection. The possible cause may instead have been intraspecific combat.<ref>{{Cite journal |last1=Rothschild |first1=Bruce |last2=O'Connor |first2=Jingmai |last3=Lozado |first3=María Cecilia |date=December 1, 2022 |title=Closer examination does not support infection as cause for enigmatic Tyrannosaurus rex mandibular pathologies |url=https://www.sciencedirect.com/science/article/pii/S0195667122002178 |journal=Cretaceous Research |language=en |volume=140 |article-number=105353 |doi=10.1016/j.cretres.2022.105353 |bibcode=2022CrRes.14005353R |s2cid=252055157 |issn=0195-6671|url-access=subscription }}</ref>

One study of ''Tyrannosaurus'' specimens with tooth marks in the bones attributable to the same genus was presented as evidence of [[cannibalism]].<ref name="HornerCurrie_et.al._2010_Trex_cannibalism"/> Tooth marks in the [[humerus]], foot bones and [[metatarsal]]s, may indicate opportunistic scavenging, rather than wounds caused by combat with another ''T. rex''.<ref name="HornerCurrie_et.al._2010_Trex_cannibalism" /><ref>{{Cite journal |last=Perkins |first=S. |date=October 29, 2015 |title=Tyrannosaurs were probably cannibals (Comment) |url=https://www.science.org/content/article/tyrannosaurs-were-probably-cannibals |journal=Science |access-date=November 2, 2015 |archive-date=October 5, 2022 |archive-url=https://web.archive.org/web/20221005112604/https://www.science.org/content/article/tyrannosaurs-were-probably-cannibals |url-status=live }}</ref> Other [[tyrannosaurids]] may also have practiced cannibalism.<ref name="HornerCurrie_et.al._2010_Trex_cannibalism" />

==Paleoecology==
[[File:Hell Creek Formation Fauna.png|thumb|upright=1.4|left|Fauna of Hell Creek (''Tyrannosaurus'' in dark red, left).]]
''Tyrannosaurus'' lived during what is referred to as the [[Lancian]] faunal stage ([[Maastrichtian]] age) at the end of the Late Cretaceous. ''Tyrannosaurus'' ranged from [[Canada]] in the north to at least New Mexico in the south of [[Laramidia]].<ref name="larson2008" />
Several notable ''Tyrannosaurus'' remains have been found in the [[Hell Creek Formation]]. During the Maastrichtian this area was [[subtropical]], with a warm and humid climate. The flora consisted mostly of [[angiosperms]], but also included trees like dawn redwood (''[[Metasequoia]]'').<ref>{{cite book |last1=Arens |first1=Nan Crystal |last2=Allen |first2=Sarah E. |title=Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas |chapter=A florule from the base of the Hell Creek Formation in the type area of eastern Montana: Implications for vegetation and climate |date=January 1, 2014 |doi=10.1130/2014.2503(06) |isbn=978-0-8137-2503-1 }}</ref> Archosaurs discovered from this formation include the [[ceratopsia]]ns ''[[Leptoceratops]]'', ''[[Torosaurus]]'', and ''[[Triceratops]]'',<ref>{{cite book|last=Ott|first=C.J.|year=2006|chapter=Cranial Anatomy and Biogeography of the First ''Leptoceratops gracilis'' (Dinosauria: Ornithischia) Specimens from the Hell Creek Formation, Southeast Montana|editor-last=Carpenter|editor-first=K.|title=Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs|publisher=Indiana University Press|pages=213–234|isbn=0-253-34817-X}}</ref> the hadrosaurid ''[[Edmontosaurus annectens]]'',<ref>{{cite journal | last1 = Campione | first1 = N.E. | last2 = Evans | first2 = D.C. | year = 2011 | title = Cranial Growth and Variation in Edmontosaurs (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous Megaherbivore Diversity in North America | journal = PLOS ONE | volume = 6 | issue = 9| article-number = e25186 | doi = 10.1371/journal.pone.0025186 | pmid = 21969872 | pmc=3182183| bibcode = 2011PLoSO...625186C | doi-access = free }}</ref> the [[Parksosauridae|parksosaurid]] ''[[Thescelosaurus]]'',<ref>{{cite book |last1=Weishampel |first1=D.B. |last2=Barrett |first2=P.M. |last3=Coria |first3=R.A. |last4=Le Loeufff |first4=J. |last5=Xu |first5=X. |last6=Zhao |first6=X. |last7=Sahni |first7=A. |last8=Gomani |first8=E.P.M. |last9=Noto |first9=C.R. |editor1-last=Weishampel |editor1-first=D.B. |editor2-last=Osmólska |editor2-first=H. |editor3-last=Dodson |editor3-first=P. |title=The Dinosauria |date=2004 |publisher=University of California Press |isbn=0-520-24209-2 |pages=517–606 |edition=2nd |chapter=Dinosaur Distribution}}</ref> the [[ankylosaur]]s ''[[Ankylosaurus]]'' and ''[[Denversaurus]]'',<ref>{{cite thesis|author=Bruns, M.E.|year=2015|title=Intraspecific variation in the armoured dinosaurs (Dinosauria: Ankylosauria)|publisher=University of Alberta Library|degree=PhD|doi=10.7939/R39K46485}}</ref> the [[pachycephalosaur]]s ''[[Pachycephalosaurus]]'', ''[[Platytholus]]'' and ''[[Sphaerotholus]]'',<ref>{{Cite journal |last1=Woodruff |first1=D. Cary |last2=Schott |first2=Ryan K. |last3=Evans |first3=David C. |date=November 15, 2023 |title=Two new species of small-bodied pachycephalosaurine (Dinosauria, Marginocephalia) from the uppermost Cretaceous of North America suggest hidden diversity in well-sampled formations |journal=Papers in Palaeontology |language=en |volume=9 |issue=6 |article-number=e1535 |doi=10.1002/spp2.1535 |bibcode=2023PPal....9E1535W |issn=2056-2799}}</ref><ref>{{Cite journal |last1=Horner |first1=John R. |last2=Goodwin |first2=Mark B. |last3=Evans |first3=David C. |date=April 14, 2023 |title=A new pachycephalosaurid from the Hell Creek Formation, Garfield County, Montana, U.S.A. |journal=Journal of Vertebrate Paleontology |volume= 42|issue= 4|article-number=e2190369 |doi=10.1080/02724634.2023.2190369 |issn=0272-4634}}</ref> the [[Paraves|paravian]] theropods ''[[Acheroraptor]]'' and ''[[Pectinodon]]'',<ref>{{cite journal|author1=Williamson, T.E.|author2=Brusatte, S.L.|year=2014|title=Small Theropod Teeth from the Late Cretaceous of the San Juan Basin, Northwestern New Mexico and Their Implications for Understanding Latest Cretaceous Dinosaur Evolution|journal=PLOS ONE|volume=9|issue=4|article-number=e93190|doi=10.1371/journal.pone.0093190|doi-access=free |pmid=24709990 |pmc=3977837 |bibcode=2014PLoSO...993190W }}</ref> other [[maniraptora]]n theropods ''[[Anzu wyliei|Anzu]]'', ''[[Eoneophron]]'', ''[[Trierarchuncus]]'' and indeterminate [[ornithomimid]]s,<ref>{{Cite journal|last1=Atkins-Weltman |first1=K. L. |last2=Simon |first2=D. J. |last3=Woodward |first3=H. N. |last4=Funston |first4=G. F. |last5=Snively |first5=E. |title=A new oviraptorosaur (Dinosauria: Theropoda) from the end-Maastrichtian Hell Creek Formation of North America |year=2024 |journal=PLOS ONE |volume=19 |issue=1 |article-number=e0294901 |doi=10.1371/journal.pone.0294901 |doi-access=free |pmid=38266012 |pmc=10807829 |bibcode=2024PLoSO..1994901A }}</ref><ref>{{cite journal |author1=Denver W. Fowler |author2=John P. Wilson |author3=Elizabeth A. Freedman Fowler |author4=Christopher R. Noto |author5=Daniel Anduza |author6=John R. Horner |year=2020 |title=''Trierarchuncus prairiensis'' gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana |journal=Cretaceous Research |volume=116 |article-number=104560 |doi=10.1016/j.cretres.2020.104560 |s2cid=225630913 |doi-access=free |bibcode=2020CrRes.11604560F }}</ref> the [[tyrannosauroid]] ''[[Nanotyrannus]]'',<ref name="Z&N25"/> and the [[azhdarchid]] [[pterosaur]] ''[[Infernodrakon]]''.<ref>{{Cite journal |last1=Thomas |first1=Henry N. |last2=Hone |first2=David W. E. |last3=Gomes |first3=Timothy |last4=Peterson |first4=Joseph E. |date=February 28, 2025 |title=''Infernodrakon hastacollis'' gen. et sp. nov., a new azhdarchid pterosaur from the Hell Creek Formation of Montana, and the pterosaur diversity of Maastrichtian North America |journal=[[Journal of Vertebrate Paleontology]] |volume=44 |issue=4 |article-number=e2442476 |doi=10.1080/02724634.2024.2442476 |issn=0272-4634}}</ref> 

[[File:Hell Creek dinosaurs and pterosaurs by durbed.jpg|thumb|''Tyrannosaurus'' and other animals of the Hell Creek Formation]]
Another formation with ''Tyrannosaurus'' remains is the [[Lance Formation]] of Wyoming. This has been interpreted as a [[bayou]] environment similar to today's Gulf Coast. The fauna was very similar to Hell Creek, but with ''[[Struthiomimus]]'' replacing its relative ''Ornithomimus''. The small ceratopsian ''[[Leptoceratops]]'' also lived in the area.<ref>{{Cite book |title=The Dinosaurs of Wyoming |last=Derstler |first=K. |publisher=Wyoming Geological Association Guidebook, 44th Annual Field Conference. Wyoming Geological Association |year=1994 |editor-last=Nelson |editor-first=G. E. |pages=127–146 |chapter=Dinosaurs of the Lance Formation in eastern Wyoming}}</ref>

In its southern range, specifically based on remains discovered from the [[North Horn Formation]] of [[Utah]], ''Tyrannosaurus rex'' lived alongside the [[Titanosauria|titanosaur]] ''[[Utetitan]]'', the [[Ceratopsidae|ceratopsid]] ''[[Torosaurus]]'' and the indeterminate [[Troodontidae|troodontid]]s and [[Hadrosauridae|hadrosaurid]]s.<ref>{{cite journal |last1=Sampson |first1=Scott D. |last2=Loewon |first2=Mark A. |title=''Tyrannosaurus rex'' from the Upper Cretaceous (Maastrichtian) North Horn Formation of Utah: Biogeographic and Paleoecologic Implications |journal=Journal of Vertebrate Paleontology |date=June 27, 2005 |volume=25 |issue=2 |pages=469–472 |doi=10.1671/0272-4634(2005)025[0469:TRFTUC]2.0.CO;2 |jstor=4524461 |s2cid=131583311 }}</ref><ref>{{cite book |last=Cifelli |first=Richard L. |author2=Nydam, Randall L. |author3=Eaton, Jeffrey G. |author4=Gardner, James D. |author5=Kirkland, James I. |year=1999 |title=Vertebrate Paleontology in Utah |chapter=Vertebrate faunas of the North Horn Formation (Upper Cretaceous–Lower Paleocene), Emery and Sanpete Counties, Utah |editor=Gillette, David D. |pages=377–388|publisher=Utah Geological Survey |location=Salt Lake City |isbn=1-55791-634-9}}</ref><ref name=Utetitan>{{Cite journal |last1=Paul |first1=Gregory S. |author1-link=Gregory S. Paul |date=October 7, 2025 |title=Stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the Late Cretaceous (Campanian-Maastrichtian) of southwestern North America |url=https://giw.utahgeology.org/giw/index.php/GIW/article/view/156 |journal=Geology of the Intermountain West |volume=12 |pages=201–220 |doi=10.31711/giw.v12.pp201-220 |archive-date=October 10, 2025 |access-date=October 9, 2025 |archive-url=https://web.archive.org/web/20251010051116/https://giw.utahgeology.org/giw/index.php/GIW/article/view/156 |url-status=live }}</ref> ''Tyrannosaurus mcraeensis'' from the [[McRae Group]] of [[New Mexico]] coexisted with the [[Ceratopsidae|ceratopsid]] ''[[Sierraceratops]]'' and possibly the titanosaur ''Alamosaurus''.<ref name=T.mcraeensis/> Potential remains identified as cf. ''Tyrannosaurus'' have also been discovered from the [[Javelina Formation]] of [[Texas]],<ref name=T.mcraeensis/> where the remains of the titanosaur (either ''Alamosaurus'' or ''Utetitan''),<ref name=Utetitan/> the ceratopsid ''[[Bravoceratops]]'', the [[pterosaur]]s ''[[Quetzalcoatlus]]'' and ''[[Wellnhopterus]]'', and possible species of troodontids and hadrosaurids are found.<ref>{{cite journal |last1=Wick |first1=Steven L. |last2=Lehman |first2=Thomas M. |title=A new ceratopsian dinosaur from the Javelina Formation (Maastrichtian) of West Texas and implications for chasmosaurine phylogeny |journal=Naturwissenschaften |date=July 1, 2013 |volume=100 |issue=7 |pages=667–682 |doi=10.1007/s00114-013-1063-0 |pmid=23728202 |bibcode=2013NW....100..667W |s2cid=16048008 }}</ref><ref name="wellnhopterus">{{cite journal |first1=B. |last1=Andres |first2=W. Jr. |last2=Langston |title=Morphology and taxonomy of ''Quetzalcoatlus'' Lawson 1975 (Pterodactyloidea: Azhdarchoidea) |journal=Journal of Vertebrate Paleontology |year=2021 |volume=41 |issue=sup1 |page=142 |doi=10.1080/02724634.2021.1907587 |bibcode=2021JVPal..41S..46A |s2cid=245125409 |issn=0272-4634|doi-access=free }}</ref><ref>{{cite journal|last1=Tweet|first1=J.S.|last2=Santucci|first2=V.L.|year=2018|title=An Inventory of Non-Avian Dinosaurs from National Park Service Areas|journal=New Mexico Museum of Natural History and Science Bulletin|volume=79|pages=703–730|url=http://npshistory.com/publications/paleontology/nmmnhs-79-703.pdf|archive-date=November 2, 2024|access-date=June 9, 2024|archive-url=https://web.archive.org/web/20241102020100/https://npshistory.com/publications/paleontology/nmmnhs-79-703.pdf|url-status=live}}</ref> Its southern range is thought to have been dominated by semi-arid inland plains, following the probable retreat of the [[Western Interior Seaway]] as global sea levels fell.<ref>{{Cite journal |last1=Jasinski |first1=S. E. |last2=Sullivan |first2=R. M. |last3=Lucas |first3=S. G. |year=2011 |title=Taxonomic composition of the Alamo Wash local fauna from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member) San Juan Basin, New Mexico |journal=Bulletin |volume=53 |pages=216–271}}</ref>

''Tyrannosaurus'' may have also inhabited Mexico's [[Lomas Coloradas Formation]] in Sonora. Though skeletal evidence is lacking, six shed and broken teeth from the fossil bed have been thoroughly compared with other theropod genera and appear to be identical to those of ''Tyrannosaurus''. If true, the evidence indicates the range of ''Tyrannosaurus'' was possibly more extensive than previously believed.<ref>{{Cite journal |last1=Serrano-Brañas |first1=C. I. |last2=Torres-Rodrígueza |first2=E. |last3=Luna |first3=P. C. R. |last4=González |first4=I. |last5=González-León |first5=C. |year=2014 |title=Tyrannosaurid teeth from the Lomas Coloradas Formation, Cabullona Group (Upper Cretaceous) Sonora, México |journal=Cretaceous Research |volume=49 |pages=163–171 |doi=10.1016/j.cretres.2014.02.018|bibcode=2014CrRes..49..163S }}</ref> It is possible that tyrannosaurs were originally Asian species, migrating to North America before the end of the Cretaceous period.<ref>{{Cite journal |last1=Brusatte |first1=S. L. |last2=Carr |first2=T. D. |year=2016 |title=The phylogeny and evolutionary history of tyrannosauroid dinosaurs |journal=[[Scientific Reports]] |volume=6 |article-number=20252 |doi=10.1038/srep20252 |pmc=4735739 |pmid=26830019|bibcode=2016NatSR...620252B }}</ref> 

===Population estimates===
[[File:Upper Cretaceous Hell Creek dinosaur census 2.svg|left|thumb|Chart of the time-averaged census for large-bodied dinosaurs from the entire Hell Creek Formation in the study area]]
According to studies published in 2021 by Charles Marshall et al., the total population of adult ''Tyrannosaurus'' at any given time was perhaps 20,000 individuals, with computer estimations also suggesting a total population no lower than 1,300 and no higher than 328,000. The authors themselves suggest that the estimate of 20,000 individuals is probably lower than what should be expected, especially when factoring in that disease pandemics could easily wipe out such a small population. Over the span of the genus' existence, it is estimated that there were about 127,000 generations and that this added up to a total of roughly 2.5 billion animals until their extinction.<ref name="nytimes2021"/><ref name="Marshall2021"/>

In the same paper, it is suggested that in a population of ''Tyrannosaurus'' adults numbering 20,000, the number of individuals living in an area the size of California could be as high as 3,800 animals, while an area the size of Washington D.C. could support a population of only two adult ''Tyrannosaurus''. The study does not take into account the number of juvenile animals in the genus present in this population estimate due to their occupation of a different niche than the adults, and thus it is likely the total population was much higher when accounting for this factor. Simultaneously, studies of living carnivores suggest that some predator populations are higher in density than others of similar weight (such as jaguars and hyenas, which are similar in weight but have vastly differing population densities). Lastly, the study suggests that in most cases, only one in 80 million ''Tyrannosaurus'' would become fossilized, while the chances were likely as high as one in every 16,000 of an individual becoming fossilized in areas that had more dense populations.<ref name="nytimes2021">{{Cite news|url=https://www.nytimes.com/2021/04/15/science/tyrannosaurus-rex-population.html |archive-url=https://ghostarchive.org/archive/20211228/https://www.nytimes.com/2021/04/15/science/tyrannosaurus-rex-population.html |archive-date=December 28, 2021 |url-access=limited|title=How Many Tyrannosaurus Rexes Ever Lived on Earth? Here's a New Clue.|first=Kenneth|last=Chang|newspaper=The New York Times|date=April 15, 2021}}{{cbignore}}</ref><ref name="Marshall2021">{{Cite journal|title=Absolute abundance and preservation rate of Tyrannosaurus rex|first1=Charles R.|last1=Marshall|first2=Daniel V.|last2=Latorre|first3=Connor J.|last3=Wilson|first4=Tanner M.|last4=Frank|first5=Katherine M.|last5=Magoulick|first6=Joshua B.|last6=Zimmt|first7=Ashley W.|last7=Poust|date=April 16, 2021|journal=Science|volume=372|issue=6539|pages=284–287|doi=10.1126/science.abc8300|pmid=33859033|bibcode=2021Sci...372..284M|doi-access=free}}</ref>

Meiri (2022) questioned the reliability of the estimates, citing uncertainty in metabolic rate, body size, sex and age-specific survival rates, habitat requirements and range size variability as shortcomings Marshall et al. did not take into account.<ref>{{Cite journal|last=Meiri|first=Shai|date=2022|title=Population sizes of T. rex cannot be precisely estimated|url=https://escholarship.org/uc/item/8mj4015f|journal=Frontiers of Biogeography|volume=14|issue=2|language=en|doi=10.21425/F5FBG53781|s2cid=245288933|doi-access=free|archive-date=February 4, 2022|access-date=February 8, 2022|archive-url=https://web.archive.org/web/20220204051249/https://escholarship.org/uc/item/8mj4015f|url-status=live}}</ref> The authors of the original publication replied that while they agree that their reported uncertainties were probably too small, their framework is flexible enough to accommodate uncerainty in physiology, and that their calculations do not depend on short-term changes in population density and geographic range, but rather on their long-term averages. Finally, they remark that they did estimate the range of reasonable survivorship curves and that they did include uncertainty in the time of onset of sexual maturity and in the growth curve by incorporating the
uncertainty in the maximum body mass.<ref>{{Cite journal|last1=Marshall|first1=Charles R.|last2=Latorre|first2=Daniel V.|last3=Wilson|first3=Connor J.|last4=Frank|first4=Tanner M.|last5=Magoulick|first5=Katherine M.|last6=Zimmt|first6=Joshua P.|last7=Poust|first7=Ashley W.|date=2022|title=With what precision can the population size of Tyrannosaurus rex be estimated? A reply to Meiri|url=https://escholarship.org/uc/item/8vv2g57c|journal=Frontiers of Biogeography|volume=14|issue=2|language=en|doi=10.21425/F5FBG55042|s2cid=245314491|doi-access=free|hdl=10852/101238|hdl-access=free|archive-date=January 21, 2022|access-date=February 8, 2022|archive-url=https://web.archive.org/web/20220121045413/https://escholarship.org/uc/item/8vv2g57c|url-status=live}} [[File:CC BY icon.svg|50px|class=noviewer]] Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License] {{Webarchive|url=https://web.archive.org/web/20171016050101/https://creativecommons.org/licenses/by/4.0/ |date=October 16, 2017 }}.</ref>

==Cultural significance==
{{Main|Tyrannosaurus in popular culture}}

[[File:King Kong vs Tyrannosaurus.jpg|alt=|right|thumb|[[King Kong]] fighting ''Tyrannosaurus'' in the 1933 film]]
''Tyrannosaurus'' is the most widely known dinosaur in [[popular culture]]. Science writer [[Riley Black]] states, "In all of prehistory, there is no animal that commands our attention quite like ''Tyrannosaurus rex'', the king of the tyrant lizards. Since the time this dinosaur was officially named in 1905, the enormous carnivore has stood as the ultimate dinosaur."<ref>{{cite book |author=Riley Black |title=The Last Days of the Dinosaurs: An Asteroid, Extinction, and the Beginning of Our World |location=New York |publisher=St Martin's Press |year=2022 |page=219 |isbn=978-1-250-27105-1 |url=https://books.google.com/books?id=6CtBEAAAQBAJ&q=%22in.all.of.prehistory%22&pg=PA1}}</ref> Paleontologist David Hone notes the popularity of ''Tyrannosaurus'' models and skeletal displays in museums and writes that films like  ''[[Jurassic Park (film)|Jurassic Park]]'' and ''[[King Kong (1933 film)|King Kong]]'' "would not have been the same without it."<ref>{{cite book|last=Hone|first=David|year=2016|title=The Tyrannosaur Chronicles: The Biology of the Tyrant Dinosaurs|publisher=Bloomsbury Publishing|page=23|isbn=978-1-4729-1127-8}}</ref> ''T. rex'' is the only dinosaur that is commonly known to the general public by its full scientific name ([[Binomial nomenclature|binomial name]]) and the scientific abbreviation ''T.&nbsp;rex'' has also come into wide usage.<ref name="brochu2003" /> [[Robert T. Bakker]] notes this in ''[[The Dinosaur Heresies]]'' and explains that, "a name like {{'}}''T. rex''{{'}} is just irresistible to the tongue."<ref name="bakker1986" />

== See also ==
* [[History of paleontology]]

==Notes==
{{notelist}}

==References==
{{Reflist}}

==Further reading==
* {{Cite journal
 | last1=Farlow |first1=J. O.
 | last2=Gatesy |first2=S. M.
 | last3=Holtz |first3=T. R. Jr.
 | last4=Hutchinson |first4=J. R.
 | last5=Robinson |first5=J. M.
 | title=Theropod Locomotion
 | journal=American Zoologist
 | volume=40
 | issue=4
 | pages=640–663
 | year=2000
 | doi=10.1093/icb/40.4.640
 | jstor=3884284
| doi-access=free | ref=none
 }}

==External links==
{{Sister project links |wikt=no |commons=Tyrannosaurus |b=Wikijunior:Dinosaurs/Tyrannosaurus |n=no |q=Tyrannosaurus |s=Tyrannosaurus and Other Cretaceous Carnivorous Dinosaurs |v=no |species=Tyrannosaurus}}
* [https://www.youtube.com/watch?v=hVJmPmb_LWY The University of Edinburgh Lecture Dr Stephen Brusatte – Tyrannosaur Discoveries Feb 20, 2015]
* [http://www.livescience.com/53877-t-rex-was-invasive-species.html 28 species in the tyrannosaur family tree, when and where they lived] [[Stephen Brusatte]] [[Thomas Carr (paleontologist)|Thomas Carr]] 2016
* [https://onesearch.slq.qld.gov.au/permalink/61SLQ_INST/dls06p/alma99274923402061 Australia's answer to T-Rex], [[State Library of Queensland]]

===Exhibits===
* [http://www.amnh.org/exhibitions/permanent-exhibitions/fossil-halls/hall-of-saurischian-dinosaurs/tyrannosaurus-rex American Museum of Natural History]

{{Theropoda|C.|state=autocollapse}}
{{Portal bar|Dinosaurs|Paleontology|United States}}
{{Taxonbar|from=Q14332}}
{{Authority control}}

[[Category:Tyrannosaurus| ]]
[[Category:Dinosaur genera]]
[[Category:Maastrichtian dinosaurs]]
[[Category:Hell Creek Formation]]
[[Category:Lance Formation]]
[[Category:Laramie Formation]]
[[Category:Scollard Formation]]
[[Category:Taxa named by Henry Fairfield Osborn]]
[[Category:Fossil taxa described in 1905]]
[[Category:Dinosaurs of Canada]]
[[Category:Dinosaurs of the United States]]
[[Category:Apex predators]]