View source for Stegosauria

{{Short description|Extinct clade of dinosaurs}}
{{automatic taxobox
| name = Stegosaurs
| fossil_range = <br>[[Middle Jurassic]] - [[Early Cretaceous]], {{fossilrange|earliest=Early Jurassic|169|100.5|latest=66}}<small>Possible [[Early Jurassic]], [[Aalenian]] and [[Maastrichtian|Late Maastrichtian]] records in the form of fossil tracks and referred fossils.<ref name=dinosauria/><ref name=NJGPA2017>{{cite journal |author=Peter M. Galton |year=2017 |title=Purported earliest bones of a plated dinosaur (Ornithischia: Stegosauria): a "dermal tail spine" and a centrum from the Aalenian-Bajocian (Middle Jurassic) of England, with comments on other early thyreophorans |journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen |volume=285 |issue=1 |pages=1–10 |doi=10.1127/njgpa/2017/0667 |bibcode=2017NJGPA.285....1G |s2cid=134361050 |url=https://zenodo.org/record/835532 }}</ref><ref name=NJGPA20172>{{cite journal |author1=Peter M. Galton |author2=Krishnan Ayyasami |year=2017 |title=Purported latest bone of a plated dinosaur (Ornithischia: Stegosauria), a "dermal plate" from the Maastrichtian (Upper Cretaceous) of southern India |journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen |volume=285 |issue=1 |pages=91–96 |doi=10.1127/njgpa/2017/0671 |bibcode=2017NJGPA.285...91G }}</ref></small>
| image = Stegosauria Infobox Panoply.png
| image_caption = Six stegosaurs (top left to bottom right):  ''[[Stegosaurus ungulatus]]'', ''[[Kentrosaurus]]'', ''[[Huayangosaurus]]'', ''[[Gigantspinosaurus]]'', ''[[Miragaia longicollum|Miragaia]]'' (or possibly ''[[Dacentrurus]]''), ''[[Tuojiangosaurus]]''
| image_upright = 1.3
| taxon = Stegosauria
| authority = [[Othniel Charles Marsh|Marsh]], 1877
| type_species = 
| type_species_authority = 
| subdivision_ranks = Subgroups<ref name="madzia2021"/><ref name="SF&C25" />
| subdivision = 
*{{extinct}}''[[Craterosaurus]]''
*{{extinct}}''[[Lexovisaurus]]''
*{{extinct}}''[[Mongolostegus]]''
*{{extinct}}''[[Monkonosaurus]]''
*{{extinct}}'''Huayangosauridae''' <small>Dong, Tang, & Zhou, 1982</small>
**{{extinct}}''[[Baiyinosaurus]]''
**{{extinct}}''[[Bashanosaurus]]''
**{{extinct}}''[[Gigantspinosaurus]]''
**{{extinct}}''[[Huayangosaurus]]''
**{{extinct}}''[[Isaberrysaura]]''
**{{extinct}}''[[Regnosaurus]]''?
*{{extinct}}'''Stegosauridae''' <small>Marsh, 1880</small>
**{{extinct}}''[[Chungkingosaurus]]''?
**{{extinct}}''[[Kentrosaurus]]''
**{{extinct}}''[[Paranthodon]]''
**{{extinct}}''[[Tuojiangosaurus]]''
**{{extinct}}'''Dacentrurinae''' <small>Mateus ''et al.'', 2009</small>
***{{extinct}}''[[Adratiklit]]''
***{{extinct}}''[[Alcovasaurus]]''
***{{extinct}}''[[Dacentrurus]]''
***{{extinct}}''[[Miragaia longicollum|Miragaia]]''
***{{extinct}}''[[Thyreosaurus]]''
**{{extinct}}'''Stegosaurinae''' <small>[[Nopcsa]], 1917</small>
***{{extinct}}''[[Chialingosaurus]]''?
***{{extinct}}''[[Hesperosaurus]]''
***{{extinct}}''[[Hypsirhophus]]''?
***{{extinct}}''[[Jiangjunosaurus]]''
***{{extinct}}''[[Loricatosaurus]]''
***{{extinct}}''[[Stegosaurus]]''
***{{extinct}}''[[Wuerhosaurus]]''
***{{extinct}}''[[Yanbeilong]]''
***{{extinct}}''[[Yingshanosaurus]]''?
}}
'''Stegosauria''' is a group of [[Herbivore|herbivorous]] [[ornithischian]] [[dinosaur]]s that lived during the [[Jurassic]] and early [[Cretaceous]] [[Period (geology)|periods]]. Stegosaurian fossils have been found mostly in the [[Northern Hemisphere]] ([[North America]], [[Europe]] and [[Asia]]), [[Africa]] and [[South America]]. Their geographical origins are unclear; the earliest unequivocal stegosaurian, ''[[Bashanosaurus primitivus]]'', was found in the [[Bathonian]] [[Shaximiao Formation]] of China.

Stegosaurians were armored dinosaurs ([[thyreophora]]ns). Originally, they did not differ much from more primitive members of that group, being small, low-slung, running animals protected by armored [[scute]]s. An early evolutionary innovation was the development of spikes as defensive weapons. Later species, belonging to a subgroup called the [[Stegosauridae]], became larger, and developed long hindlimbs that no longer allowed them to run. This increased the importance of active defence by the [[thagomizer]], which could ward off even large predators because the tail was in a higher position, pointing horizontally to the rear from the broad pelvis. Stegosaurids had complex arrays of spikes and plates running along their backs, hips and tails.

Stegosauria includes two families, the primitive '''Huayangosauridae''' and the more derived '''Stegosauridae'''. The stegosaurids like all other stegosaurians were quadrupedal herbivores that exhibited the characteristic stegosaurian dorsal dermal plates. These large, thin, erect plates are thought to be aligned parasagittally from the neck to near the end of the tail. The end of the tail has pairs of spikes, sometimes referred to as a [[thagomizer]].<ref name=":1">{{Cite journal|last1=Billon-Bruyat|first1=Jean-Paul|last2=Marty|first2=Daniel|date=2010-09-04|title=Preface: Symposium on Stegosauria proceedings|journal=[[Swiss Journal of Geosciences]]|language=en|volume=103|issue=2|pages=139–141|doi=10.1007/s00015-010-0027-z|issn=1661-8726|doi-access=free}}</ref><ref name=":2">{{Cite journal|last=Sereno|first=Paul C.|date=1999-06-25|title=The Evolution of Dinosaurs|journal=Science|language=en|volume=284|issue=5423|pages=2137–2147|doi=10.1126/science.284.5423.2137|issn=0036-8075|pmid=10381873}}</ref> It may be that this is the only scientific term derived from a joke (in this case a ''[[The Far Side]]'' comic). Although defense, thermo-regulation and display have been theorized to be the possible functions of these dorsal plates, a study of the ontogenetic histology of the plates and spikes suggests that the plates serve different functions at different stages of the stegosaurids' life histories. The terminal spikes in the tail are thought to have been used in old adults, at least, as a weapon for defence.<ref name=":4">{{Cite journal|last1=Hayashi|first1=Shoji|last2=Carpenter|first2=Kenneth|last3=Watabe|first3=Mahito|last4=McWHINNEY|first4=Lorrie A.|date=2012-01-01|title=Ontogenetic histology of Stegosaurus plates and spikes|journal=Palaeontology|language=en|volume=55|issue=1|pages=145–161|doi=10.1111/j.1475-4983.2011.01122.x|issn=1475-4983|doi-access=free|bibcode=2012Palgy..55..145H }}</ref> However, the function of stegosaurid plates and spikes, at different life stages, still remains a matter of great debate.

The first stegosaurian finds in the early 19th century were fragmentary. Better fossil material, of the genus ''[[Dacentrurus]]'', was discovered in 1874 in England. Soon after, in 1877, the first nearly-complete skeleton was discovered in the United States. Professor [[Othniel Charles Marsh]] that year classified such specimens in the new genus ''[[Stegosaurus]]'', from which the group acquired its name, and which is still by far the most famous stegosaurian. During the latter half of the twentieth century, many important Chinese finds were made, representing about half of the presently known diversity of stegosaurians.

==History of research==
The first known discovery of a possible stegosaurian was probably made in the early nineteenth century in England. It consisted of a lower jaw fragment and was in 1848 named ''[[Regnosaurus]]''. In 1845, in the area of the present state of [[South Africa]], remains were discovered that much later would be named ''[[Paranthodon]]''. In 1874, other remains from England were named ''[[Craterosaurus]]''. All three [[Taxon|taxa]] were based on fragmentary material and were not recognised as possible stegosaurians until the twentieth century. They gave no reason to suspect the existence of a new distinctive group of dinosaurs.
[[File:Position of bones in skeleton sketched by Arthur Lakes.jpg|left|thumb|''Stegosaurus'' bones illustrated by Arthur Lakes in 1879]]
In 1874, extensive remains of what was clearly a large herbivore equipped with spikes were uncovered in England; the first partial stegosaurian skeleton known.<ref name="maidment2010"/> They were named ''Omosaurus'' by [[Richard Owen]] in 1875. Later, this name was shown to be preoccupied by the [[phytosaur]] ''[[Omosaurus]]'' and the stegosaurian was renamed ''[[Dacentrurus]]''. Other English nineteenth century and early twentieth century finds would be assigned to ''Omosaurus''; later they would, together with French fossils, be partly renamed ''[[Lexovisaurus]]'' and ''[[Loricatosaurus]]''.

In 1877, [[Arthur Lakes]], a fossil hunter working for Professor [[Othniel Charles Marsh]], in [[Wyoming]] excavated a fossil that Marsh the same year named ''[[Stegosaurus]]''. At first, Marsh still entertained some incorrect notions about its morphology. He assumed that the plates formed a flat skin cover — hence the name, meaning "roof saurian" — and that the animal was bipedal with the spikes sticking out sideways from the rear of the skull. A succession of additional discoveries from the [[Como Bluff]] sites allowed a quick update of the presumed build. In 1882, Marsh was able to publish the first skeletal reconstruction of a stegosaur. Hereby, stegosaurians became much better known to the general public. The American finds at the time represented the bulk of known stegosaurian fossils, with about twenty skeletons collected.<ref name="maidment2010"/>

The next important discovery was made when a German expedition to the [[Tendaguru]], then part of [[German East Africa]], from 1909 to 1912 excavated over a thousand bones of ''[[Kentrosaurus]]''. The finds increased the known variability of the group, ''Kentrosaurus'' being rather small and having long rows of spikes on the hip and tail.
[[File:Stegosaurus ungulatus model Lull 1910.png|thumb|left|An early [[life restoration]] of a ''Stegosaurus'' from 1910]]
From the 1950s onwards, the geology of China was systematically surveyed in detail and infrastructural works led to a vast increase of digging activities in that country. This resulted in a new wave of Chinese stegosaurian discoveries, starting with ''[[Chialingosaurus]]'' in 1957. Chinese finds of the 1970s and 1980s included ''[[Wuerhosaurus]]'', ''[[Tuojiangosaurus]]'', ''[[Chungkingosaurus]]'', ''[[Huayangosaurus]]'', ''[[Yingshanosaurus]]'' and ''[[Gigantspinosaurus]]''. This increased the age range of good fossil stegosaurian material, as they represented the first relatively complete skeletons from the [[Middle Jurassic]] and the [[Early Cretaceous]]. Especially important was ''Huayangosaurus'', which provided unique information about the early evolution of the group.

Towards the end of the twentieth century, the so-called [[Dinosaur Renaissance]] took place in which a vast increase in scientific attention was given to the Dinosauria. In 2007, ''[[Jiangjunosaurus]]'' was reported, the first Chinese dinosaur named since 1994. Nevertheless, European and North-American sites have become productive again during the 1990s, ''[[Miragaia longicollum|Miragaia]]'' having been found in the [[Lourinhã Formation]] in [[Portugal]] and a number of relatively complete ''[[Hesperosaurus]]'' skeletons having been excavated in Wyoming. Apart from the fossils per se, important new insights have been gained by applying the method of [[cladistics]], allowing for the first time to exactly calculate stegosaurian evolutionary relationships.

==Description==
Stegosaurids are distinguished from other stegosaurians in that the former have lost the plesiomorphic pre-maxillary teeth and lateral scute rows along the trunk.<ref name=":5">Sereno, Paul C., and Dong Zhimin. "The Skull of the Basal Stegosaur Huayangosaurus Taibaii and a Cladistic Diagnosis of Stegosauria." ''Journal of Vertebrate Paleontology'' 12, no. 3 (1992): 318-43. {{JSTOR|4523456}}.</ref> Furthermore, stegosaurids have long narrow skulls and longer hindlimbs compared to their forelimbs.<ref name=":2" /> However, these two features are not diagnostic of Stegosauridae because they may also be present in non-stegosaurid stegosaurians.<ref name=dinosauria/>

===Skull===
Stegosaurians had characteristic small, long, flat, narrow heads and a horn-covered beak or [[beak#Anatomy|rhamphotheca]],<ref name=dinosauria/> which covered the front of the snout (two [[premaxilla]]ries) and lower jaw (a single [[predentary]]) bones. Similar structures are seen in [[turtle]]s and [[bird]]s. Apart from ''[[Huayangosaurus]]'', stegosaurians subsequently lost all premaxillary teeth within the upper beak. ''Huayangosaurus'' still had seven per side. The upper and lower jaws are equipped with rows of small teeth. Later species have a vertical bone plate covering the outer side of the lower jaw teeth. The structure of the upper jaw, with a low ridge above, and running parallel to, the tooth row, indicates the presence of a fleshy cheek. In stegosaurians, the typical [[archosauria]]n skull opening, the [[antorbital fenestra]] in front of the eye socket, is small, sometimes reduced to a narrow horizontal slit. In general, stegosaurids have proportionally long, low and narrow snouts with a deep mandible, compared to that of ''[[Huayangosaurus]]''. Stegosaurids also lack premaxillary teeth.<ref name=":5"/>

===Postcranial skeleton===
All stegosaurians are [[quadruped]]al, with hoof-like toes on all four limbs. All stegosaurians after ''Huayangosaurus'' have forelimbs much shorter than their hindlimbs. Their hindlimbs are long and straight, designed to carry the weight of the animal while stepping. The [[Knee#Articular bodies|condyles]] of the lower thighbone are short from the front to the rear. This would have limited the supported rotation of the knee joint, making running impossible. ''Huayangosaurus'' had a thighbone like a running animal. The upper leg was always longer than the lower leg.

''Huayangosaurus'' had relatively long and slender arms. The forelimbs of later forms are very robust, with a massive [[humerus]] and [[ulna]]. The [[Carpal bones|wrist bones]] were reinforced by a fusion into two blocks, an ulnar and a radial. The front feet of stegosaurians are commonly depicted in art and in museum displays with fingers splayed out and slanted downward. However, in this position, most bones in the hand would be disarticulated. In reality, the hand bones of stegosaurians were arranged into vertical columns, with the main fingers, orientated outwards, forming a tube-like structure. This is similar to the hands of [[Sauropoda|sauropod dinosaurs]], and is also supported by evidence from stegosaurian footprints and fossils found in a lifelike pose.<ref name=senter2010>{{cite journal|last=Senter|first=P.|year=2010|title=Evidence for a sauropod-like metacarpal configuration in stegosaurian dinosaurs|journal=Acta Palaeontologica Polonica|volume=55|issue=3|pages=427–432|doi=10.4202/app.2009.1105|s2cid=53328847|url=http://doc.rero.ch/record/32124/files/PAL_E2887.pdf|doi-access=free}}</ref>
[[File:DMSN dinosaurs.jpg|upright=1.35|thumb|''Stegosaurus'' mount showing to a good effect the high neck posture, the throat ossicles and the robust shoulder girdle and forelimbs]]
The long hindlimbs elevated the tail base, such that the tail pointed out behind the animal almost horizontally from that high position. While walking, the tail would not have sloped downwards as this would have impeded the function of the tail base retractor muscles, to pull the thighbones backwards. However, it has been suggested by [[Bob Bakker|Robert Thomas Bakker]] that stegosaurians could rear on their hind legs to reach higher layers of plants, the tail then being used as a "third leg". The mobility of the tail was increased by a reduction or absence of ossified tendons, that with many Ornithischia stiffen the hip region. ''Huayangosaurus'' still possessed them. In species that had short forelimbs, the relatively short torso towards the front curved strongly downwards. The dorsal vertebrae typically were very high, with very tall [[neural arch]]es and [[transverse processes]] pointing obliquely upwards to almost the level of the neural spine top. Stegosaurian back vertebrae can easily be identified by this unique configuration. The tall neural arches often house deep [[neural canal]]s; enlarged canals in the [[sacral vertebrae]] have given rise to the incorrect notion of a "second brain". Despite the downwards curvature of the rump, the neck base was not very low and the head was held a considerable distance off the ground. The neck was flexible and moderately long. ''Huayangosaurus'' still had the probably original number of nine cervical vertebrae; ''[[Miragaia longicollum|Miragaia]]'' has an elongated neck with seventeen.<ref name=mateus2010>{{Cite journal |last=Mateus |first=Octávio |author2=Maidment, Susannah C.R. |author3= Christiansen, Nicolai A.  |title=A new long-necked 'sauropod-mimic' stegosaur and the evolution of the plated dinosaurs |journal=Proceedings of the Royal Society B: Biological Sciences |year=2009 |volume=276 |doi=10.1098/rspb.2008.1909 |pmid=19324778 |issue=1663 |pages=1815–21 |pmc=2674496}}</ref>

The stegosaurian [[shoulder girdle]] was very robust. In ''Huayangosaurus'', the [[acromion]], a process on the lower front edge of the [[shoulderblade]], was moderately developed; the [[coracoid]] was about as wide as the lower end of the [[scapula]], with which it formed the [[shoulder joint]]. Later forms tend to have a strongly expanded acromion, while the coracoid, largely attached to the acromion, no longer extends to the rear lower corner of the scapula.

The stegosaurian pelvis was originally moderately large, as shown by ''Huayangosaurus''. Later species, however, convergent to the Ankylosauria developed very broad [[Pelvis|pelves]], in which the [[iliac bone]]s formed wide horizontal plates with flaring front blades to allow for an enormous belly-gut. The ilia were attached to the sacral vertebrae via a sacral yoke formed by fused sacral ribs. ''Huayangosaurus'' still had rather long and obliquely oriented [[ischium|ischia]] and [[pubic bone]]s. In more derived species, these became more horizontal and shorter to the rear, while the front prepubic process lengthened.

===Armor and ornamention===
Like all [[Thyreophora]], stegosaurians were protected by bony [[scute]]s that were not part of the skeleton proper but skin ossifications instead: the so-called [[osteoderm]]s. ''Huayangosaurus'' had several types. On its neck, back, and tail were two rows of paired small vertical plates and spikes. The very tail end bore a small club. Each flank had a row of smaller osteoderms, culminating in a long shoulder spine in front, curving to the rear.{{citation needed|date=July 2024}} Later forms show very variable configurations, combining plates of various shape and size on the neck and front torso with spikes more to the rear of the animal. They seem to have lost the tail club and the flank rows are apparently absent also, with the exception of the shoulder spine, still shown by ''[[Kentrosaurus]]'' and extremely developed, as its name indicates, in ''[[Gigantspinosaurus]]''. As far as is known, all forms possessed some sort of thagomizer, though these are rarely preserved articulated allowing to establish the exact arrangement. A fossil of ''[[Chungkingosaurus]]'' sp. has been reported with three pairs of spikes pointing outwards and a fourth pair pointing to the rear.<ref>Z. Dong, S. Zhou, and Y. Zhang, 1983, "[Dinosaurs from the Jurassic of Sichuan]". ''Palaeontologia Sinica, New Series C'', '''162'''(23): 1-136</ref> The most derived species, like ''[[Stegosaurus]]'', ''[[Hesperosaurus]]'' and ''[[Wuerhosaurus]]'', have very large and flat back plates. Stegosaurid plates have a thick base and central portion, but are transversely thin elsewhere. The plates become remarkably large and thin in ''Stegosaurus''. They are found in varying sizes along the dorsum, with the central region of the back usually having the largest and tallest plates. The arrangement of these parasagittal dorsal plates has been intensely debated in the past. Discoverer [[Othniel Charles Marsh]] suggested a single median row of plates running post-cranially along the longitudinal axis<ref>Marsh, O. C. (1891). Restoration of Stegosaurus. American Journal of Science, 3rd series, 42, 179–182.</ref> and [[Richard Swann Lull|Lull]] argued in favour of bilaterally paired arrangement throughout the series.<ref>Lull, R. S. (1910a). Stegosaurus ungulatus Marsh, recently mounted at the Peabody Museum of Yale University. American Journal of Science, 4th series, 30, 361–377</ref> Current scientific consensus lies in the arrangement proposed by [[Charles W. Gilmore|Gilmore]] - two parasagittal rows of staggered alternates, after the discovery of an almost complete skeleton preserved in this manner in rock.<ref name="gilmore14"/> Furthermore, no two plates share the same size and shape, making the possibility of bilaterally paired rows even less likely. Plates are usually found with distinct vascular grooves on their lateral surfaces, suggesting the presence of a circulatory network. Stegosaurids also have osteoderms on the throat in the form of small depressed ossicles and two pairs of elongated spike-like tail-spines.<ref name=dinosauria/> With ''Stegosaurus'' fossils also ossicles have been found in the throat region, bony skin discs that protected the lower neck.<ref>{{cite book|title=The Evolution and Extinction of the Dinosaurs|year=2005|chapter=Stegosauria:Hot Plates|editor1=Fastovsky D.E. |editor2=Weishampel D.B. |author1=Fastovsky D.E. |author2=Weishampel D.B. |pages=107–130|publisher=Cambridge University Press|isbn=978-0-521-81172-9|edition=2nd}}</ref>

Many basal stegosaurs like ''[[Gigantspinosaurus]]'' and ''Huayangosaurus'' have been discovered with parascapular spines, or spines emerging from the shoulder region. Among stegosaurids, only ''Kentrosaurus'' has been found with parascapular spines, which project posteriorly out of the lower part of the shoulder plates. These spines are long, rounded and comma-shaped in lateral view and have an enlarged base. ''Loricatosaurus'' was also believed to have a parascapular spine, but Maidment ''et al''. (2008) observed that the discovered specimen, from which the spine is described, has a completely different morphology than the parascapular spine specimens of other stegosaurs. They suggest it may be a fragmentary tail spine instead.<ref name="maidment2008"/> Stegosaurids also lack lateral scute rows that run longitudinally on either side of the trunk in ''Huayangosaurus'' and [[Ankylosauria|ankylosaurs]], indicating yet another secondary loss of a plesiomorphic characters.<ref name=":5" /> However, the absence of lateral scutes as well as pre-maxillary teeth mentioned above are not specifically diagnostic of stegosaurids, since these features are also present in some other stegosaurians, whose phylogenetic relationships are unclear.<ref name=":5" /><ref name="maidment2008"/>

The discovery of an impression of the skin covering the dorsal plates has implications for all possible functions of stegosaurian plates. Christiansen and Tschopp (2010)<ref name=":8">{{Cite journal|last1=Christiansen|first1=Nicolai A.|last2=Tschopp|first2=Emanuel|date=2010-09-07|title=Exceptional stegosaur integument impressions from the Upper Jurassic Morrison Formation of Wyoming|journal=[[Swiss Journal of Geosciences]]|language=en|volume=103|issue=2|pages=163–171|doi=10.1007/s00015-010-0026-0|s2cid=129246092|issn=1661-8726|doi-access=free|bibcode=2010SwJG..103..163C }}</ref> found that the skin was smooth with long, parallel, shallow grooves indicating a keratinous structure covering the plates. The addition of [[beta-keratin]], a strong protein, would indeed allow the plates to bear more weight, suggesting they may have been used for active defense. A keratinous covering would also allow greater surface area for the plates to be uses as a mating display structures, which could be potentially coloured like the beaks of modern birds. At the same time this finding implies that the use of plates for thermo-regulation may be less likely because the keratinous covering would make heat transfer from the bone highly ineffective.<ref name=":8"/>

==Classification==
[[File:Stegosauridae Trinity.jpg|thumb|left|250px|Illustration comparing three stegosaurids by Danny Cicchetti, 2013.]]In 1877, Othniel Marsh discovered and named ''Stegosaurus armatus'', from which the name of the family 'Stegosauridae' was erected in 1880.<ref name="maidment2010"/> In comparison to basal stegosaurians, notable synapomorphies of Stegosauridae include a large antitrochanter (supracetabular process) in the [[Ilium (bone)|ilium]], a long prepubic process and long [[femur]] relative to the length of the [[humerus]].<ref>David	E. Fastovsky , David B. Weishampel. The Evolution and Extinction of	the Dinosaurs. p. 123</ref> Furthermore, stegosaurid sacral ribs are T-shaped in parasagittal cross-section<ref name=dinosauria/> and the dorsal [[vertebra]]e have an elongated neural arch.<ref name="maidment2010"/> The first exact clade definition of Stegosauria was given by [[Peter Malcolm Galton]] in 1997: all [[thyreophora]]n [[Ornithischia]] more closely related to ''Stegosaurus'' than to ''[[Ankylosaurus]]''.<ref>Galton, P.M., 1997, "Stegosauria", pp. 701-703 in: P.J. Currie and K. Padian (eds.), ''Encyclopedia of Dinosaurs'', Academic Press, San Diego</ref> This definition was formalized in the ''[[PhyloCode]]'' by Daniel Madzia and colleagues in 2021 as "the largest clade containing ''[[Stegosaurus stenops]]'', but not ''[[Ankylosaurus magniventris]]''".<ref name="madzia2021">{{cite journal|last1=Madzia|first1=D.|last2=Arbour|first2=V.M.|last3=Boyd|first3=C.A.|last4=Farke|first4=A.A.|last5=Cruzado-Caballero|first5=P.|last6=Evans|first6=D.C.|year=2021|title=The phylogenetic nomenclature of ornithischian dinosaurs|journal=PeerJ|volume=9|pages=e12362|doi=10.7717/peerj.12362|pmid=34966571|pmc=8667728 |doi-access=free }}</ref> Thus defined, the Stegosauria are by definition the [[sister group]] of the [[Ankylosauria]] within the [[Eurypoda]]. The vast majority of stegosaurian dinosaurs thus far recovered belong to the Stegosauridae, which lived in the later part of the Jurassic and early Cretaceous, and which were defined by [[Paul Sereno]] as all stegosaurians more closely related to ''Stegosaurus'' than to ''Huayangosaurus''.<ref>Sereno, P.C., 1998, "A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria", ''Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen'' '''210''': 41-83</ref> This definition was also formalized in the ''[[PhyloCode]]'' by Daniel Madzia and colleagues in 2021 as "the largest clade containing ''[[Stegosaurus stenops]]'', but not ''[[Huayangosaurus taibaii]]''".<ref name="madzia2021"/> They include per definition the well-known ''[[Stegosaurus]]''. This group is widespread, with members across the Northern Hemisphere, [[Africa]] and [[South America]].<ref name=Pereda-Suberbiola2013>{{cite journal|last=Pereda-Suberbiola|first=Xabier|author2=Galton, Peter M. |author3=Mallison, Heinrich |author4= Novas, Fernando |title=A plated dinosaur (Ornithischia, Stegosauria) from the Early Cretaceous of Argentina, South America: an evaluation|journal=Alcheringa: An Australasian Journal of Palaeontology|year=2013|volume=37|issue=1|pages=65–78|doi=10.1080/03115518.2012.702531|bibcode=2013Alch...37...65P |s2cid=128632458|hdl=11336/67876|hdl-access=free}}</ref><ref>{{Cite journal |last1=Rauhut |first1=Oliver W. M. |last2=Carballido |first2=José Luis |last3=Pol |first3=Diego |date=2020-12-10 |title=First osteological record of a stegosaur (Dinosauria, Ornithischia) from the Upper Jurassic of South America |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1862133 |journal=Journal of Vertebrate Paleontology |language=en |volume=40 |issue=6 |pages=e1862133 |doi=10.1080/02724634.2020.1862133 |bibcode=2020JVPal..40E2133R |s2cid=234161169 |issn=0272-4634|url-access=subscription }}</ref>

Huayangosauridae (derived from ''[[Huayangosaurus]]'', "[[Sichuan|Huayang]] reptile") is a family of stegosaurian [[dinosaur]]s from the [[Jurassic]] of [[China]].<ref name="dong1982">{{cite journal|last1=Dong|first1=Z.|last2=Tang|first2=Z.|last3=Zhou|first3=S.W.|year=1982|title=四川自贡大山铺蜀龙动物群简报1.剑龙|trans-title=Note on the new Mid-Jurassic stegosaur from Sichuan Basin, China|language=zh-cn|journal=Vertebrata PalAsiatica|volume=20|issue=1|pages=83–87|url=http://www.ivpp.cas.cn/cbw/gjzdwxb/xbwzxz/200904/P020100311296596082254.pdf}}</ref> The group is defined as all taxa closer to the namesake genus ''Huayangosaurus'' than ''[[Stegosaurus]]'', and was originally named as the family Huayangosaurinae by [[Dong Zhiming]] and colleagues in the description of ''Huayangosaurus''.<ref name="dong1982"/><ref name="madzia2021">{{cite journal|last1=Madzia|first1=D.|last2=Arbour|first2=V.M.|last3=Boyd|first3=C.A.|last4=Farke|first4=A.A.|last5=Cruzado-Caballero|first5=P.|last6=Evans|first6=D.C.|year=2021|title=The phylogenetic nomenclature of ornithischian dinosaurs|journal=PeerJ|volume=9|pages=e12362|doi=10.7717/peerj.12362|pmid=34966571|pmc=8667728 |doi-access=free }}</ref> Huayangosaurinae was originally differentiated by the remaining taxa within [[Stegosauridae]] by the presence of [[teeth]] in the {{dinogloss|premaxilla}}, an {{dinogloss|antorbital fenestra}}, and a {{dinogloss|mandibular fenestra}}. Huayangosaurinae, known from the [[Middle Jurassic]] of the [[Shaximiao Formation]], was proposed to be intermediate between [[Scelidosaurinae]] and [[Stegosaurinae]], suggesting that the origins of stegosaurs lay in Asia.<ref name="dong1982"/> Following phylogenetic analyses, Huayangosauridae was expanded to also include the taxon ''[[Chungkingosaurus]]'', known from specimens from younger Late Jurassic deposits of the Shaximiao Formation.<ref name="maidment2008">{{Cite journal|last1=Maidment|first1=S.C.R.|last2=Norman|first2=D.B.|last3=Barrett|first3=P.M.|last4=Upchurch|first4=P.|year=2008|title=Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia)|journal=Journal of Systematic Palaeontology|volume=6|issue=4|pages=367–407|doi=10.1017/S1477201908002459|bibcode=2008JSPal...6..367M |s2cid=85673680 }}</ref> Huayangosauridae is either the sister taxon to all other stegosaurs,<ref name="maidment2008"/><ref name="maidment2010">{{cite journal|last=Maidment|first=S.C.R.|year=2010|title=Stegosauria: a historical review of the body fossil record and phylogenetic relationships|journal=[[Swiss Journal of Geosciences]]|volume=103|issue=Supplement 2, Symposium on Stegosauria|pages=199–210|doi=10.1007/s00015-010-0023-3|bibcode=2010SwJG..103..199M |s2cid=84415016 }}</ref> or close to the origin of the clade, with taxa like ''[[Gigantspinosaurus]]'' or ''[[Isaberrysaura]]'' outside the Stegosauridae-Huayangosauridae split.<ref name="madzia2021"/><ref name="maidment2010"/> Huayangosauridae was formally defined in [[2021 in paleontology|2021]] by Daniel Madzia and colleagues, who used the previous definitions of all taxa closer to ''Huayangosaurus taibaii'' than ''[[Stegosaurus stenops]]''.<ref name="madzia2021"/>

In 2017, Raven and Maidment published a comprehensive phylogenetic framework including most valid stegosaurian genera. Several subsequent publications expanded and corrected this matrix based on novel taxa and revised anatomical interpretations. In 2025, Sánchez-Fenollosa & Cobos compiled these variations and other observations into an updated and expanded dataset. The authors further coined the name '''Neostegosauria''' for the clade comprising the Dacentrurinae (including ''Kentrosaurus'') and the Stegosaurinae. These results are displayed in the [[cladogram]] below:<ref name="SF&C25">{{cite journal|last1=Sánchez-Fenollosa |first1=Sergio |last2=Cobos |first2=Alberto |year=2025 |title=New insights into the phylogeny and skull evolution of stegosaurian dinosaurs: An extraordinary cranium from the European Late Jurassic (Dinosauria: Stegosauria) |journal=Vertebrate Zoology |volume=75 |pages=147–171 |doi=10.3897/vz.75.e146618 |doi-access=free}}</ref>

{{clade|style=font-size:90%; line-height:90%;
|{{clade
 |1=[[Ankylosauria]] <div style="{{MirrorH}}">[[File:Ankylosaurus magniventris by sphenaphinae.png|60 px]]</div>
 |label2='''Stegosauria'''
 |2={{clade
  |label1='''Huayangosauridae'''
  |1={{clade
   |1=''[[Isaberrysaura]]'' <div style="{{MirrorH}}">[[File:Isaberrysaura mollensis.png|60px]]</div>
   |2={{clade
   |1={{clade
    |1=''[[Bashanosaurus]]'' <div style="{{MirrorH}}">[[File: Bashanosaurus primitivus.png|60px]]</div>
    |2=''[[Huayangosaurus]]'' <div style="{{MirrorH}}">[[File:Huayangosaurus taibaii.png|60px]]</div> }}
    |3={{clade
     |1=''[[Baiyinosaurus]]'' <div style="{{MirrorH}}">[[File:Baiyinosaurus baojiensis.png|60px]]</div>
     |2=''[[Gigantspinosaurus]]'' <div style="{{MirrorH}}">[[File:Gigantspinosaurus sichuanensis.png|60px]]</div> }} }} }}
     |label3='''Stegosauridae'''
     |3={{clade
  |1=''[[Chungkingosaurus]]'' <div style="{{MirrorH}}">[[File:Chungkingosaurus jiangbeiensis.png|60px]]</div>
  |2={{clade
  |1={{clade
   |1=''[[Tuojiangosaurus]]'' <div style="{{MirrorH}}">[[File:Tuojiangosaurus multispinus.png|60px]]</div>
   |2=''[[Paranthodon]]'' <div style="{{MirrorH}}">[[File:Paranthodon africanus.png|60px]]</div> }}
   |label3='''Neostegosauria'''
   |3={{clade
   |label1='''Dacentrurinae'''
   |1={{clade
|1=''[[Alcovasaurus]]'' <div style="{{MirrorH}}">[[File:Alcovasaurus longispinus.png|60px]]</div>
|2={{clade
 |1=''[[Kentrosaurus]]'' <div style="{{MirrorH}}">[[File:Kentrosaurus aethiopicus.png|60px]]</div>
 |2={{clade
  |1=''[[Thyreosaurus]]'' <div style="{{MirrorH}}">[[File:Thyreosaurus atlasicus.png|60px]]</div>
  |2={{clade
   |1=''[[Adratiklit]]'' <div style="{{MirrorH}}">[[File:Adratiklit boulahfa.png|60px]]</div>
   |2=''[[Dacentrurus]]'' <div style="{{MirrorH}}">[[File:Dacentrurus armatus.png|68px]]</div><br>{{small|(including ''[[Miragaia longicollum|Miragaia]]'')}} }} }} }} }}
   |label3='''Stegosaurinae'''
   |3={{clade
   |1={{clade
   |1={{clade
|1=[[Qigu Formation]] [[Angustungui|stegosaur]]
|2=''[[Loricatosaurus]]'' <div style="{{MirrorH}}">[[File:Loricatosaurus priscus.png|60px]]</div> }}
|3={{clade
 |1=''[[Hesperosaurus]]'' <div style="{{MirrorH}}">[[File:Hesperosaurus mjosi.png|55px]]</div>
 |2=''[[Stegosaurus stenops]]'' <div style="{{MirrorH}}">[[File:Stegosaurus stenops.png|60px]]</div> }} }}
 |3={{clade
|1=''[[Jiangjunosaurus]]'' <div style="{{MirrorH}}">[[File:Jiangjunosaurus junggarensis.png|60px]]</div>
|2={{clade
 |1=[[Hekou Group]] stegosaur
 |2={{clade
  |1=''[[Wuerhosaurus homheni]]'' <div style="{{MirrorH}}">[[File:Wuerhosaurus homheni.png|65px]]</div>
  |2=''[[Yanbeilong]]'' <div style="{{MirrorH}}">[[File:Yanbeilong ultimus.png|60px]]</div>
}} }} }} }} }} }} }} }} }}|label1=[[Eurypoda]]}}

===Undescribed species===
To date, several genera from China bearing names have been proposed but not formally described, including "[[Changdusaurus]]".<ref name="maidment2006">{{cite journal| last= Maidment| first= Susannah C.R.|author2=Guangbiao Wei | title= A review of the Late Jurassic stegosaurs (Dinosauria, Stegosauria) from the People's Republic of China| journal = Geological Magazine| volume = 143| issue = 5| pages = 621–634| year = 2006| url = http://geolmag.geoscienceworld.org/cgi/content/abstract/143/5/621| doi = 10.1017/S0016756806002500| bibcode= 2006GeoM..143..621M| s2cid= 83661067| url-access = subscription}}</ref> Until formal descriptions are published, these genera are regarded as ''[[nomen nudum|nomina nuda]]''.

===Evolutionary history===
[[File:Huayangosaurus BW.jpg|upright=1.35|thumb|''Huayangosaurus'' is the oldest and most basal stegosaurian of which good material is known, giving an impression of the build of the earliest members of the group]]
Like the spikes and shields of [[ankylosaur]]s, the [[bony plate]]s and spines of stegosaurians evolved from the low-keeled osteoderms characteristic of [[Basal (phylogenetics)|basal]] thyreophorans.<ref name="Norman">Norman, David (2001). "''Scelidosaurus'', the earliest complete dinosaur" in ''The Armored Dinosaurs'', pp 3-24. Bloomington: Indiana University Press. {{ISBN|0-253-33964-2}}.</ref> One such described genus, ''[[Scelidosaurus]]'', is proposed to be morphologically close to the [[last common ancestor]] of the clade uniting stegosaurians and ankylosaurians, the [[Eurypoda]].<ref name=CompleteDinosaur>{{cite book|last=Galton|first=Peter|title=The Complete Dinosaur|year=1997|publisher=Indiana University Press|location=Bloomington|isbn=9780253213136|chapter-url=https://books.google.com/books?id=FOViD-lDPy0C&pg=PA291|editor=James O. Farlow |editor2=M. K. Brett-Surman|chapter=21: ''Stegosaurs''}}</ref> [[Peter Galton|Galton]] (2019) interpreted plates of an armored dinosaur from the [[Lower Jurassic]] ([[Sinemurian]]-[[Pliensbachian]]) Lower [[Kota Formation]] of [[India]] as fossils of a member of [[Ankylosauria]]; the author argued that this finding indicates a probable early [[Early Jurassic]] origin for both Ankylosauria and its [[sister group]] Stegosauria.<ref>{{Cite journal|author=Peter M. Galton |year=2019 |title=Earliest record of an ankylosaurian dinosaur (Ornithischia: Thyreophora): Dermal armor from Lower Kota Formation (Lower Jurassic) of India |journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen |volume=291 |issue=2 |pages=205–219 |doi=10.1127/njgpa/2019/0800 |bibcode=2019NJGPA.291..205G |s2cid=134302379 }}</ref> Footprints attributed to the [[ichnotaxon]] ''[[Deltapodus]] brodricki'' from the Middle Jurassic ([[Aalenian]]) of [[England]] represent the oldest probable record of stegosaurians reported so far.<ref name=NJGPA2017 /> Outside that, there are assigned fossils to stegosauria from the [[Toarcian]]: the specimen "IVPP V.219", a chimaera with bones of the sauropod ''[[Sanpasaurus]]'' is known from the Maanshan Member of the [[Ziliujing Formation]].<ref>{{Cite web|url=https://paleobiodb.org/classic/basicCollectionSearch?collection_no=140254|title = PBDB}}</ref> The earliest possible trackways of stegosaurians are discovered from the [[Hettangian]]-aged deposits of [[France]], indicating a possibly earlier origin.<ref name=dinosauria/> The perhaps most basal known stegosaurian, the four-metre-long ''Huayangosaurus'', is still close to ''Scelidosaurus'' in build, with a higher and shorter skull, a short neck, a low torso, long slender forelimbs, short hindlimbs, large condyles on the thighbone, a narrow pelvis, long ischial and pubic shafts, and a relatively long tail. Its small tail club might be a [[Thyreophora|eurypodan]] [[synapomorphy]]. ''Huayangosaurus'' lived during the [[Bathonian]] stage of the [[Middle Jurassic]], about 166&nbsp;million years ago.

A few million years later, during the [[Callovian]]-[[Oxfordian (stage)|Oxfordian]], from China much larger species are known, with long, "graviportal" (adapted for moving only in a slow manner on land due to a high body weight) hindlimbs: ''[[Chungkingosaurus]]'', ''[[Chialingosaurus]]'', ''[[Tuojiangosaurus]]'' and ''[[Gigantspinosaurus]]''. Most of these are considered members of the derived [[Stegosauridae]]. ''[[Lexovisaurus]]'' and ''[[Loricatosaurus]]'', stegosaurid finds from England and France of approximately equivalent age to the Chinese specimens, are likely the same [[taxon]]. During the [[Late Jurassic]], stegosaurids seem to have experienced their greatest radiation. In Europe, ''[[Dacentrurus]]'' and the closely related ''[[Miragaia longicollum|Miragaia]]'' were present. While older finds had been limited to the northern continents, in this phase [[Gondwana]] was colonised also as shown by ''[[Kentrosaurus]]'' living in [[Africa]]. No unequivocal stegosaurian fossils have been reported from [[South-America]], India, [[Madagascar]], Australia, or [[Antarctica]], though. A Late Jurassic Chinese stegosaurian is ''[[Jiangjunosaurus]]''. The most derived Jurassic stegosaurians are known from [[North-America]]: ''Stegosaurus'' (perhaps several species thereof) and the somewhat older ''[[Hesperosaurus]]''. ''Stegosaurus'' was quite large (some specimens indicate a length of at least seven metres), had high plates, no shoulder spine, and a short, deep rump.

From the [[Early Cretaceous]], far fewer finds are known and it seems that the group had declined in diversity. Some fragmentary fossils have been described, such as ''[[Craterosaurus]]'' from England and ''[[Paranthodon]]'' from [[South Africa]]. Up until recently, the only substantial discoveries were those of ''[[Wuerhosaurus]]'' from Northern China, the exact age of which is highly uncertain<ref name="Holtz2011">{{Cite book | last1 = Holtz | first1 = Thomas R. Jr. | last2 = Rey | first2 = Luis V. | title = Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages | url = https://archive.org/details/dinosaursmostcom00holt | year = 2007 | publisher = Random House | location = New York | isbn = 978-0-375-82419-7 | url-access = registration }}</ref> More recent discoveries from Asia however would later begin to fill out the Early Cretaceous diversity of the group. Indeterminate stegosaurs are known from the Early Cretaceous of [[Siberia]], including the [[Ilek Formation]]<ref>{{Cite journal|last1=Leshchinskiy|first1=S. V.|last2=Fayngerts|first2=A. V.|last3=Ivantsov|first3=S. V.|date=2019-10-20|title=Bol'shoi Ilek as the ilek formation stratotype of the Lower Cretaceous, and the new dinosaur and mammoth faunae site in the south-east of Western Siberia|url=https://journals.eco-vector.com/0869-5652/article/view/17790|journal=Доклады Академии Наук СССР|language=Ru|volume=488|issue=5|pages=513–516|doi=10.31857/S0869-56524885513-516|issn=0869-5652|doi-access=free}}</ref> and [[Batylykh Formation]].<ref>{{Cite journal|last1=Skutschas|first1=Pavel P.|last2=Gvozdkova|first2=Vera A.|last3=Averianov|first3=Alexander O.|last4=Lopatin|first4=Alexey V.|last5=Martin|first5=Thomas|last6=Schellhorn|first6=Rico|last7=Kolosov|first7=Petr N.|last8=Markova|first8=Valentina D.|last9=Kolchanov|first9=Veniamin V.|last10=Grigoriev|first10=Dmitry V.|last11=Kuzmin|first11=Ivan T.|date=2021-03-17|editor-last=Pardo-Pérez|editor-first=Judith|title=Wear patterns and dental functioning in an Early Cretaceous stegosaur from Yakutia, Eastern Russia|journal=PLOS ONE|language=en|volume=16|issue=3|pages=e0248163|doi=10.1371/journal.pone.0248163|issn=1932-6203|pmc=7968641|pmid=33730093|bibcode=2021PLoSO..1648163S|doi-access=free}}</ref> The youngest known definitive remains of stegosaurs are those of ''[[Mongolostegus]]'' from Mongolia, a stegosaurine from the [[Hekou Group]] of China, and ''[[Yanbeilong]]'' of the [[Zuoyun Formation]] of China, all of which date to the [[Aptian]]-[[Albian]].<ref>{{Cite journal|last1=Tumanova|first1=T. A.|last2=Alifanov|first2=V. R.|date=2018-12-01|title=First Record of Stegosaur (Ornithischia, Dinosauria) from the Aptian–Albian of Mongolia|url=https://doi.org/10.1134/S0031030118140186|journal=Paleontological Journal|language=en|volume=52|issue=14|pages=1771–1779|doi=10.1134/S0031030118140186|bibcode=2018PalJ...52.1771T |s2cid=91559457|issn=1555-6174|url-access=subscription}}</ref><ref name=HekouStegosaur>{{Cite journal |last1=Li |first1=Ning |last2=Li |first2=Daqing |last3=Peng |first3=Guangzhao |last4=You |first4=Hailu |date=2024 |title=The first stegosaurian dinosaur from Gansu Province, China |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667124000259 |journal=[[Cretaceous Research]] |volume=158 |language=en |at=105852 |doi=10.1016/j.cretres.2024.105852 |issue=in press|bibcode=2024CrRes.15805852L |url-access=subscription }}</ref><ref name="Yanbeilong">{{Cite journal |last1=Jia |first1=Lei |last2=Li |first2=Ning |last3=Dong |first3=Liyang |last4=Shi |first4=Jianru |last5=Kang |first5=Zhishuai |last6=Wang |first6=Suozhu |last7=Xu |first7=Shichao |last8=You |first8=Hailu |date=2024-01-31 |title=A new stegosaur from the late Early Cretaceous of Zuoyun, Shanxi Province, China |journal=[[Historical Biology]] |volume=37 |issue=2 |language=en |pages=420–429 |doi=10.1080/08912963.2024.2308214 |issn=0891-2963}}</ref>

It has often been suggested that the decline in stegosaur diversity was part of a Jurassic-Cretaceous transition, where [[angiosperms]] become the dominant plants, causing a [[faunal turnover]] where new groups of herbivores evolved.<ref>Bakker, R.T., 1998, "Dinosaur mid-life crisis: the Jurassic-Cretaceous transition in Wyoming and Colorado", In: S.G. Lucas, J.I. Kirkland, & J.W. Estep (eds.) ''Lower and Middle Cretaceous Terrestrial Ecosystems; New Mexico Museum of Natural History and Science Bulletin'', '''14''': 67-77</ref> Although in general the case for such a causal relation is poorly supported by the data, stegosaurians are an exception in that their decline coincides with that of the [[Cycadophyta]].<ref>Butler, R.J., Barrett, P.M., Kenrick, P. and Penn, M.G., 2009, "Diversity patterns amongst herbivorous dinosaurs and plants during the Cretaceous: implications for hypotheses of dinosaur/angiosperm co-evolution", ''Journal of Evolutionary Biology'', '''22''': 446–459</ref>

Though Late Cretaceous stegosaurian fossils have been reported, these have mostly turned out to be misidentified. A well-known example is ''[[Dravidosaurus]]'', known from [[Coniacian]] fossils found in India. Though originally thought to be stegosaurian, in 1991 these badly-eroded fossils were suggested to instead have been based on [[plesiosauria]]n pelvis and hindlimb material,<ref>Chatterjee, S., and Rudra, D.K., 1996, "KT events in India: impact, rifting, volcanism and dinosaur extinction," in: Novas & Molnar, eds., ''Proceedings of the Gondwanan Dinosaur Symposium, Brisbane, Memoirs of the Queensland Museum'', '''39'''(3): iv + 489–731 : 489-532</ref> and none of the fossils are demonstrably stegosaurian.<ref>Wilson, J. A., Barrett, P. M., & Carrano, M. T. (2011). An associated partial skeleton of ''Jainosaurus cf. septentrionalis'' (Dinosauria: Sauropoda) from the Late Cretaceous of Chhota Simla, central India. ''Palaeontology'', 54(5), 981-998.</ref> The reinterpretation of ''Dravidosaurus'' as a plesiosaur wasn't accepted by [[Peter Galton|Galton]] and Upchurch (2004), who stated that the skull and plates of ''Dravidosaurus'' are certainly not plesiosaurian, and noted the need to redescribe the fossil material of ''Dravidosaurus''.<ref name=dinosauria>{{cite book |author1=Peter M. Galton |author2=Paul Upchurch |editor1=David B. Weishampel |editor-link=David B. Weishampel |editor2=Peter Dodson |editor3=Halszka Osmólska |editor3-link=Halszka Osmólska |title=The Dinosauria |edition=2nd |year=2004|publisher=University of California Press |place=Berkeley |isbn=978-0-520-24209-8 |pages=343–362 |chapter=Stegosauria }}</ref> A purported stegosaurian dermal plate was reported from the latest Cretaceous ([[Maastrichtian]]) [[Kallamedu Formation]] (southern India); however, Galton & Ayyasami (2017) interpreted the specimen as a bone of a sauropod dinosaur. Nevertheless, the authors considered the survival of stegosaurians into the Maastrichtian to be possible, noting the presence of the stegosaurian ichnotaxon ''[[Deltapodus]]'' in the Maastrichtian [[Lameta Formation]] (western India).<ref name=NJGPA20172 />

==Paleobiology==

===Plate function===
In an [[Ontogeny|ontogenetic]] histological analysis of ''Stegosaurus'' plates and spikes, Hayashi ''et al''. (2012)<ref name=":4" /> examined their structure and function through juveniles to old adults. They found that throughout the ontogeny, the dorsal osteoderms are composed of dense ossified collagen fibres in both the [[Cortical bone|cortical]] and [[Cancellous bone|cancellous]] sections of the bone, suggesting that plates and spikes are formed from the direct [[Mineralization (biology)|mineralization]] of already existing fibrous networks in the skin. However, the many structural features, seen in the spikes and plates of old adults specimens, are acquired at different stages of development. Extensive vascular networks form in the plates during the change from juveniles to young adults and persist in old adults but spikes acquire a thick cortex with a large axial vascular channel only in old adults. Hayashi ''et al''. argue that the formation of nourishing vascular networks in young adults supported the growth of large plates. This would have enhanced the size of the animal, which may have helped attract mates and deter rivals.<ref name=":4" /> Furthermore, the presence of the vascular networks in the plates of the young adult indicate a secondary use of the plates as a thermoregulatory device for heat loss much like the [[elephant]] ear, [[toucan]] bill or [[alligator]] osteoderms. The thickening of the cortical section of the bone and the compaction of bone in the terminal tail-spikes in old adults suggest that they were used as defence weapons, but not until an ontogenetically late stage. The development of the large axial channel in old adults from small canals in young adults, facilitated the further enlargement of the spikes by increasing the amount of nourishment supplied. On the other hand, plates do not show a similar degree of bone compaction or cortical thickening indicating they would not be capable of taking much weight from above. This suggests they were not as important as spikes in active defense.<ref name=":4" />

The protective nature of dorsal plates has also been questioned in the past - Davitashvili (1961) noted that narrow dorsal location of the plates still left the sides vulnerable. Since the pattern of plates and spines vary between species, he suggested it could be important for intraspecific recognition and as a display for sexual selection.<ref name=dinosauria/> This is corroborated by Spassov's (1982) observations that the plates are arranged for maximum visible effect when viewed laterally during non-aggressive agonistic behaviour, as opposed to from a head-on aggressive stance.<ref>Spassov, N. B. (1982). The ‘‘bizarre’’ dorsal plates of stegosaurs: ethological approach. Comptes rendus de l’academie bulgare des Sciences, 35, 367–370.</ref>

===Trace fossils===
Stegosaurian tracks were first recognized in 1996 from a hindprint-only [[trackway]] discovered at the [[Cleveland-Lloyd Dinosaur Quarry|Cleveland-Lloyd quarry]], which is located near Price, Utah.<ref name="foster-stegosaur-tracks">"Walk and Don't Look Back: The Footprints; Stegosaurs" in Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pg. 238</ref> Two years later, a new [[Ichnotaxon|ichnogenus]] called ''[[Stegopodus]]'' was erected for another set of stegosaurian tracks which were found near [[Arches National Park]], also in Utah.<ref name="foster-stegosaur-tracks"/> Unlike the first, this trackway preserved traces of the forefeet. Fossil remains indicate that stegosaurians have five digits on the forefeet and three weight-bearing digits on the hind feet.<ref name="foster-stegosaur-tracks"/> From this, scientists were able to predict the appearance of stegosaurian tracks in 1990, six years in advance of the first actual discovery of [[Morrison Formation|Morrison]] stegosaurian tracks.<ref name="foster-stegosaur-tracks"/> More trackways have been found since the erection of ''Stegopodus''. None, however, have preserved traces of the front feet and stegosaurian traces remain rare.<ref name="foster-stegosaur-tracks"/>

''[[Deltapodus]]'' is an ichnogenus attributed as stegosaurian prints, and are known across Europe,<ref name=mateus2011/> North Africa,<ref>{{Cite journal|last1=BELVEDERE|first1=MATTEO|last2=MIETTO|first2=PAOLO|date=January 2010|title=First evidence of stegosaurianDeltapodusfootprints in North Africa (Iouaridène Formation, Upper Jurassic, Morocco)|journal=Palaeontology|volume=53|issue=1|pages=233–240|doi=10.1111/j.1475-4983.2009.00928.x|s2cid=140670546 |issn=0031-0239|doi-access=free|bibcode=2010Palgy..53..233B }}</ref> and China.<ref name="Xing 68–76">{{Cite journal|last1=Xing|first1=Lida|last2=Lockley|first2=Martin G.|last3=Persons|first3=W. Scott|last4=Klein|first4=Hendrik|last5=Romilio|first5=Anthony|last6=Wang|first6=Donghao|last7=Wang|first7=Miaoyan|title=Stegosaur Track Assemblage from Xinjiang, China, Featuring the Smallest Known Stegosaur Record|date=2021-02-28|url=https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/36/2/68/595155/STEGOSAUR-TRACK-ASSEMBLAGE-FROM-XINJIANG-CHINA|journal=PALAIOS|language=en|volume=36|issue=2|pages=68–76|doi=10.2110/palo.2020.036|bibcode=2021Palai..36...68X|s2cid=233129489|issn=0883-1351|url-access=subscription}}</ref> One ''Deltapodus'' footprint measures less than 6&nbsp;cm in length and represents the smallest known stegosaurian track.<ref name="Xing 68–76"/><ref>{{Cite web|last1=Queensl|first1=The University of|last2=Lucia|first2=Australia Brisbane St|last3=Gatton|first3=QLD 4072 +61 7 3365 1111 Other Campuses: UQ|last4=Maps|first4=UQ Herston|last5=Queensl|first5=Directions © 2021 The University of|title=Tiny cat-sized stegosaur leaves its mark|url=https://www.uq.edu.au/news/article/2021/04/tiny-cat-sized-stegosaur-leaves-its-mark|access-date=2021-04-25|website=UQ News|language=en}}</ref> Some tracks preserve exquisite scaly skin pattern.<ref name=mateus2011>{{Cite journal|last1=Mateus|first1=Octávio|last2=Milàn|first2=Jesper|last3=Romano|first3=Michael|last4=Whyte|first4=Martin A.|date=September 2011|title=New Finds of Stegosaur Tracks from the Upper Jurassic Lourinhã Formation, Portugal|url=http://www.app.pan.pl/article/item/app20090055.html|journal=Acta Palaeontologica Polonica|language=en|volume=56|issue=3|pages=651–658|doi=10.4202/app.2009.0055|s2cid=55869900 |issn=0567-7920|doi-access=free}}</ref>

Australia's 'Dinosaur Coast' in [[Broome, Western Australia|Broome]], Western Australia includes tracks of several different thyreophoran track-makers. Of these, the ichnogenus ''Garbina'' (a Nyulnyulan word for 'shield') and ''Luluichnus'' (honours the late Paddy Roe, OAM who went by the name 'Lulu') have been considered registered by stegosaurs.<ref>{{Cite journal|last1=Salisbury|first1=Steven W.|last2=Romilio|first2=Anthony|last3=Herne|first3=Matthew C.|last4=Tucker|first4=Ryan T.|last5=Nair|first5=Jay P.|date=2016-12-12|title=The Dinosaurian Ichnofauna of the Lower Cretaceous (Valanginian–Barremian) Broome Sandstone of the Walmadany Area (James Price Point), Dampier Peninsula, Western Australia|journal=Journal of Vertebrate Paleontology|volume=36|issue=sup1|pages=1–152|doi=10.1080/02724634.2016.1269539|issn=0272-4634|doi-access=free|bibcode=2016JVPal..36S...1S }}</ref> ''Garbina'' includes the largest stegosaur tracks measuring 80&nbsp;cm in length. Trackway data show ''Garbina'' track-makers were capable of bipedal and quadrupedal progression, suggesting an adaptation to facultative bipedalism amongst some stegosaurs.

While has no body fossil evidence currently known for stegosaurs, handprints from underground coal mines near [[Oakey, Queensland|Oakey]], Queensland, resembling ''Garbina'' tracks suggests their occurrence in this country from at least the Middle to Upper Jurassic (Callovian–Tithonian).<ref>{{Cite journal|last1=Romilio|first1=Anthony|last2=Salisbury|first2=Steven W.|last3=Jannel|first3=Andréas|date=2020-06-12|title=Footprints of large theropod dinosaurs in the Middle–UpperJurassic (lower Callovian–lower Tithonian) Walloon Coal Measures of southern Queensland, Australia.|url=https://doi.org/10.1080/08912963.2020.1772252|journal=Historical Biology|volume=33|issue=10|pages=2135–2146|doi=10.1080/08912963.2020.1772252|s2cid=225692077|issn=0891-2963|url-access=subscription}}</ref> A single plaster cast of one of these handprints is in the collections of the [[Queensland Museum]].

=== Tail spikes ===
[[File:FieldMuseum5 Chicago.jpg|thumb|250px|right|A fossil melee involving a stegosaurian (''[[Tuojiangosaurus]]'') and a mid-sized [[theropod]] (''[[Monolophosaurus]]''), [[Field Museum]] in [[Chicago]]]]
There has been debate about whether the spikes were used simply for display, as posited by Gilmore in 1914,<ref name="gilmore14">{{cite journal|author=Gilmore, C. W.|year=1914|title=Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus ''Stegosaurus''|url=https://archive.org/details/osteologyofarmor00gilm|journal=Series: Smithsonian Institution. United States National Museum. Bulletin 89|publisher=Government Printing Office, Washington|issue=89}}</ref> or used as a weapon. [[Robert T. Bakker|Robert Bakker]] noted that it is likely that the stegosaur tail was much more flexible than those of other [[ornithischia]]n dinosaurs because it lacked ossified tendons, thus lending credence to the idea of the tail as a weapon. He also observed that ''[[Stegosaurus]]'' could have maneuvered its rear easily by keeping its large hindlimbs stationary and pushing off with its very powerfully muscled but short forelimbs, allowing it to swivel deftly to deal with attack.<ref name="bakker86">{{cite book|author=Bakker, R. T.|url=https://archive.org/details/dinosaurheresies0000bakk|title=The Dinosaur Heresies|publisher=William Morrow|year=1986|location=New York|isbn=9780688042875|url-access=registration}}{{ISBN?}}{{page needed|date=June 2020}}</ref> In 2010, analysis of a digitized model of ''[[Kentrosaurus|Kentrosaurus aethiopicus]]'' showed that the tail could bring the thagomizer around to the sides of the dinosaur, possibly striking an attacker beside it.<ref name="NaishDK">{{cite web|author=Naish, Darren|year=2010|title=Heinrich's digital Kentrosaurus: the SJG stegosaur special, part II|url=http://scienceblogs.com/tetrapodzoology/2011/01/heinrichs_digital_kentrosaurus.php|url-status=dead|archive-url=https://web.archive.org/web/20110109004732/http://scienceblogs.com/tetrapodzoology/2011/01/heinrichs_digital_kentrosaurus.php|archive-date=January 9, 2011|access-date=January 19, 2011|work=Tetrapod Zoology}}</ref>

In 2001, a study of tail spikes by McWhinney et al.,<ref>{{cite book|author=McWhinney, L. A.; Rothschild, B. M. & Carpenter, K.|title=The Armored Dinosaurs|publisher=Indiana University Press|year=2001|isbn=978-0-253-33964-5|editor=Carpenter, Kenneth|pages=141–56|chapter=Posttraumatic Chronic [[Osteomyelitis]] in ''Stegosaurus'' dermal spikes}}</ref> showed a high incidence of trauma-related damage. This too supports the theory that the spikes were used in combat. There is also evidence for ''Stegosaurus'' defending itself, in the form of an ''[[Allosaurus]]'' tail vertebra with a partially healed puncture wound that fits a ''Stegosaurus'' tail spike.<ref name="CSMW2005">{{cite book|last=Carpenter|first=Kenneth|url=https://archive.org/details/carnivorousdinos00carp|title=The Carnivorous Dinosaurs|author2=Sanders, Frank|author3=McWhinney, Lorrie A.|author4=Wood, Lowell|publisher=Indiana University Press|year=2005|isbn=978-0-253-34539-4|editor=Carpenter, Kenneth|location=Bloomington and Indianapolis|page=[https://archive.org/details/carnivorousdinos00carp/page/n330 325]|chapter=Evidence for predator-prey relationships: Examples for ''Allosaurus'' and ''Stegosaurus''|url-access=limited|name-list-style=amp}}</ref> ''Stegosaurus stenops'' had four dermal spikes, each about {{cvt|60|-|90|cm|ft|0}} long. Discoveries of articulated stegosaur armor show that, at least in some species, these spikes protruded horizontally from the tail, not vertically as is often depicted. Initially, Marsh described ''S. armatus'' as having eight spikes in its tail, unlike ''S. stenops''. However, recent research re-examined this and concluded this species also had four.<ref name="Marsh77">{{cite journal|last1=Marsh|first1=O. C|year=1877|title=A new order of extinct Reptilia (Stegosauria) from the Jurassic of the Rocky Mountains|url=https://zenodo.org/record/1450038|journal=American Journal of Science|volume=14|issue=84|pages=513–14|bibcode=1877AmJS...14..513M|doi=10.2475/ajs.s3-14.84.513|s2cid=130078453}}</ref><ref name="8spike">{{cite book|author=Carpenter, K. & Galton, P. M.|title=The Armored Dinosaurs|publisher=Indiana University Press|year=2001|isbn=978-0-253-33964-5|editor=Carpenter, Kenneth|pages=76–102|chapter=Othniel Charles Marsh and the Eight-Spiked ''Stegosaurus''}}</ref>

=== Posture ===
A digital articulation and manipulation of digital scans of specimen material of ''Kentrosaurus'' inferred that stegosaurids may have used an erect limb posture, like that of most mammals, for habitual locomotion while using a sprawled crocodilian pose for defensive behavior. The sprawled pose would allow them to tolerate the large lateral forces used in swinging the spiked tail against predators as a clubbing device.<ref name=":9">{{Cite journal|last=Mallison|first=Heinrich|date=2010-09-07|title=CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus Hennig 1915|journal=[[Swiss Journal of Geosciences]]|language=en|volume=103|issue=2|pages=211–233|doi=10.1007/s00015-010-0024-2|s2cid=132746786|issn=1661-8726|doi-access=free|bibcode=2010SwJG..103..211M }}</ref>

=== Sexual dimorphism ===
[[File:Hypothetical silhouettes of male and female S. mjosi.tif|thumb|Hypothetical sexual dimorphism of ''[[Hesperosaurus]] mjosi'', including variation in plate shape and coloration]]
There have been several findings of possible [[sexual dimorphism]] in stegosaurids. Saitta (2015)<ref>{{Cite journal|last=Saitta|first=Evan Thomas|date=2015-04-22|title=Evidence for Sexual Dimorphism in the Plated Dinosaur Stegosaurus mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Upper Jurassic) of Western USA|journal=PLOS ONE|volume=10|issue=4|pages=e0123503|doi=10.1371/journal.pone.0123503|issn=1932-6203|pmc=4406738|pmid=25901727|doi-access=free|bibcode=2015PLoSO..1023503S }}</ref> presents evidence of two morphs of ''Hesperosaurus'' dorsal plates, with one morph having a wide, oval plate with a surface area 45% larger than the narrow, tall morph. Considering that dorsal plates most likely functioned as display structures and that the wide oval shape allowed a broad continuous display, Saitta assigns the wider morph with larger surface area as male.

[[Kevin Padian]], a paleontologist at the University of California, Berkeley, remarked that Saitta had misidentified features in his specimen's bone tissue sections and said "there's no evidence the animal has stopped growing". Paidan also expressed ethical concerns about the use of private specimens in the study.<ref name=":11">{{Cite web|url=https://www.science.org/content/article/dino-sexing-study-slammed-critics|title=Dino 'sexing' study slammed by critics|date=2015-04-22|website=Science {{!}} AAAS|access-date=2016-06-04}}</ref>

''Kentrosaurus'', ''Dacentrurus'' and ''Stegosaurus'' are also suggested to have exhibited dimorphism in the form of three extra sacral ribs in the females.<ref name=dinosauria/>

=== Feeding ===
In order to explore the feeding habits of stegosaurids, Reichel (2010)<ref name=":10">{{Cite journal|last=Reichel|first=Miriam|date=2010-08-31|title=A model for the bite mechanics in the herbivorous dinosaur Stegosaurus (Ornithischia, Stegosauridae)|journal=[[Swiss Journal of Geosciences]]|language=en|volume=103|issue=2|pages=235–240|doi=10.1007/s00015-010-0025-1|s2cid=84869720|issn=1661-8726|doi-access=free|bibcode=2010SwJG..103..235R }}</ref> created a 3-D model of ''Stegosaurus'' teeth using the software [[ZBrush]]. The model finds that the bite forces of ''Stegosaurus'' was significantly weaker than that of [[Labrador Retriever|Labradors]], [[wolves]] and humans. The finding suggests that these dinosaurs would be capable of breaking smaller branches and leaves with their teeth, but would not be able to bite through a thick object (12&nbsp;mm or more in diameter). Parrish ''et al''.'s (2004)<ref>{{Cite journal|last1=Parrish|first1=Judith Totman|last2=Peterson|first2=Fred|last3=Turner|first3=Christine E|date=2004-05-15|title=Jurassic "savannah"—plant taphonomy and climate of the Morrison Formation (Upper Jurassic, Western USA)|journal=Sedimentary Geology|series=Reconstruction of the Extinct Ecosystem of the Upper Jurassic Morrison Formation|volume=167|issue=3–4|pages=137–162|doi=10.1016/j.sedgeo.2004.01.004|bibcode=2004SedG..167..137P |url=http://doc.rero.ch/record/14574/files/PAL_E1788.pdf }}</ref> description of Jurassic flora in the stegosaurid-rich [[Morrison Formation]] supports this finding. The flora during this time-period was dominated by seasonal small, fast-growing herbaceous plants, which stegosaurids could consume easily if Reichel's reconstruction is accurate.<ref name=":10" />

Mallison (2010)<ref name=":9" /> suggested that ''Kentrosaurus'' may have used a tripodal stance on their hindlimbs and tail to double the foraging height from the general low browsing height under one metre for stegosaurids. This challenged the view that stegosaurs are primarily low vegetation feeders because of their small heads, short necks and short forelimbs, since the tripodal stance would also give them access to young trees and high bushes.

Another piece of evidence suggesting that some stegosaurids may have consumed more than just low vegetation was the discovery of the long-necked stegosaurid ''Miragaia longicollum''. This dinosaur's neck has at least 17 cervical vertebrae achieved through the transformation of thoracic vertebrae into cervical vertebrae and possible lengthening of the centrum. This is more than most [[Sauropoda|sauropod]] dinosaurs, which also achieved the elongation of the neck through similar mechanisms and had access to fodder higher off the ground.<ref name=mateus2010/>

Evidence from [[Sakha Republic|Yakutia]] suggests that [[Early Cretaceous]] stegosaurs living in high latitude environments were capable of palinal jaw motion and exhibited high rates of tooth replacement and short tooth formation time.<ref>{{Cite journal |last1=Skutschas |first1=Pavel P. |last2=Gvozdkova |first2=Vera A. |last3=Averianov |first3=Alexander O. |last4=Lopatin |first4=Alexey V. |last5=Martin |first5=Thomas |last6=Schellhorn |first6=Rico |last7=Kolosov |first7=Petr N. |last8=Markova |first8=Valentina D. |last9=Kolchanov |first9=Veniamin V. |last10=Grigoriev |first10=Dmitry V. |last11=Kuzmin |first11=Ivan T. |last12=Vitenko |first12=Dmitry D. |date=17 March 2021 |editor-last=Pardo-Pérez |editor-first=Judith |title=Wear patterns and dental functioning in an Early Cretaceous stegosaur from Yakutia, Eastern Russia |journal=[[PLOS ONE]] |language=en |volume=16 |issue=3 |pages=e0248163 |doi=10.1371/journal.pone.0248163 |doi-access=free |issn=1932-6203 |pmc=7968641 |pmid=33730093 |bibcode=2021PLoSO..1648163S }}</ref>

==References==
{{Reflist}}

==External links==
{{Commons category}}
{{Wikispecies}}
{{see also|Timeline of stegosaur research}}

* [http://palaeos.com/vertebrates/ornithischia/stegosauria.html Stegosauria on Palaeos.com]
* https://web.archive.org/web/20080727011652/http://www.kheper.net/evolution/dinosauria/Stegosauria.htm

{{Ornithischia|H.}}
{{Stegosauria|S.}}
{{Taxonbar|from=Q131484}}

[[Category:Stegosauria| ]]
[[Category:Dinosaur clades]]