View source for Tuatara

{{Short description|Species of reptile}}
{{About|the animal}}
{{Good article}}
{{Cs1 config|name-list-style=vanc|display-authors=6}}
{{Use New Zealand English|date=July 2024}}
{{Use dmy dates|date=September 2020}}
{{Speciesbox
| name = Tuatara
| fossil_range = Early [[Miocene]] – present, {{fossilrange| 19|0|earliest=19}}<ref>{{cite web |title=''Sphenodon'' |website=Paleobiology Database |url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=92231&is_real_user=1 |archive-url=https://web.archive.org/web/20200715230031/https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=92231&is_real_user=1 |archive-date=15 July 2020}}</ref>
| image = Tuatara (5205719005).jpg
| image_caption = Northern tuatara<br />(''Sphenodon punctatus punctatus'')
| status = LC
| status_system = IUCN3.1
| status_ref = <ref name=IUCN2>{{cite web | url=https://www.doc.govt.nz/nature/conservation-status/#at-risk | title=Conservation status of plants and animals }}</ref><ref name=IUCN>{{Cite web|url=https://www.iucnredlist.org/species/131735762/120191347|title=IUCN Red List of Threatened Species |date=25 February 2019 }}</ref>
| status2 = REL
| status2_system = NZTCS
| status2_ref = <ref name ="NZTCS">{{cite web |title=''Sphenodon punctatus''. NZTCS |url=https://nztcs.org.nz/assessments/123941 |website=nztcs.org.nz |access-date=3 April 2023}}</ref>
| parent_authority = [[John Edward Gray|Gray]], 1831 ([[conserved name]])
| genus = Sphenodon
| species = punctatus
| authority = (Gray, 1842) (conserved name)
| range_map = World.distribution.rhynchocephalia.colour contrast.png
| range_map_caption = Native range (New Zealand)
| range_map2 = North Island Map tuatara.PNG
| range_map2_caption = Current distribution of tuatara (in black):<ref name="Daugherty_1990"/><ref name=recovery>{{cite report |author=Gaze, P. |title=Tuatara recovery plan 2001–2011 |series=Threatened Species Recovery Plan |volume=47 |department=Biodiversity Recovery Unit, Department of Conservation |publisher=Government of New Zealand |year=2001 |url=http://www.doc.govt.nz/upload/documents/science-and-technical/TSRP47.pdf |access-date=2 June 2007 |isbn=978-0-478-22131-2 |archive-url=https://web.archive.org/web/20111105132732/http://www.doc.govt.nz/upload/documents/science-and-technical/TSRP47.pdf |archive-date=5 November 2011}}</ref><ref>{{cite news |author=Beston, A. |date=25 October 2003 |title=Tuatara release |newspaper=[[New Zealand Herald]] |url=http://www.tiritirimatangi.org.nz/Articles/NZ%20Herald%20Articles%20-%20Tuatara%20Release.pdf |access-date=11 September 2007 |archive-url=https://web.archive.org/web/20071004201202/http://www.tiritirimatangi.org.nz/Articles/NZ%20Herald%20Articles%20-%20Tuatara%20Release.pdf | archive-date=4 October 2007}}</ref> Circles represent the North Island tuatara, and squares the Brothers Island tuatara. Symbols may represent up to seven islands.
| synonyms = * ''Sphaenodon'' <br />{{small|Gray, 1831 ([[Conserved name|rejected name]])}}
* ''Hatteria'' <br />{{small|Gray, 1842 (rejected name)}}
* ''Rhynchocephalus'' <br />{{small|[[Richard Owen|Owen]], 1845 (rejected name)}}
}}

The '''tuatara''' ({{IPAc-en|t|uː|ə|ˈ|t|ɑːr|ə}}, {{IPA|mi|ˈtʉ.a.ta.ɾa|lang|link=yes}}; '''''Sphenodon punctatus''''') is a species of [[reptile]] [[endemic]] to [[New Zealand]]. Despite its close resemblance to [[lizard]]s, it is the only extant member of a distinct lineage, the previously highly diverse order [[Rhynchocephalia]].<ref name="TerraNature">{{cite web |publisher=TerraNature Trust |title=Tuatara |website=New Zealand Ecology |series=Living Fossils |year=2004 |url =http://www.terranature.org/tuatara.htm| access-date=10 November 2006 |archive-url=https://web.archive.org/web/20170503163100/http://www.terranature.org/tuatara.htm |archive-date=3 May 2017}}</ref> The name {{lang|mi|tuatara}} is derived from the [[Māori language]]   and means "peaks on the back".<ref name="KCC">{{cite web |title=The Tuatara |website=Kiwi Conservation Club |series=Fact Sheets |publisher=Royal Forest and Bird Protection Society of New Zealand |year=2009 |url=http://www.kcc.org.nz/tuatara |access-date=13 September 2017 |archive-url=https://web.archive.org/web/20151016044037/http://www.kcc.org.nz/tuatara |archive-date=16 October 2015}}</ref>

The single extant [[species]] of tuatara{{efn|A second species, the Brothers Island tuatara ''S.&nbsp;guntheri'' {{small|([[Walter Buller|Buller]], 1877)}}, was recognised in 1989,<ref name="san diego" /> but since 2009 it has been reclassified as a subspecies'', S.&nbsp;p.&nbsp;guntheri''.<ref>{{cite book |author=Cree, A. |title=Tuatara: Biology and conservation of a venerable survivor |publisher=Canterbury University Press |year=2014 |isbn=978-1-927145-44-9}}</ref><ref name="Hay">{{cite journal |vauthors=Hay JM, Sarre SD, Lambert DM, Allendorf FW, Daugherty CH |year=2010 |title=Genetic diversity and taxonomy: a reassessment of species designation in tuatara (''Sphenodon'': Reptilia) |url=https://link.springer.com/article/10.1007/s10592-009-9952-7 |journal=Conservation Genetics |volume=11 |pages=1063–1081 |bibcode=2010ConG...11.1063H |doi=10.1007/s10592-009-9952-7 |s2cid=24965201 |hdl-access=free |number=3 |hdl=10072/30480|url-access=subscription }}</ref>}} is the only surviving member of its order, which was highly diverse during the [[Mesozoic]] era.<ref name="Herrera-Flores 2017" /> Rhynchocephalians first appeared in the fossil record during the [[Middle Triassic]], around 244-241.5 million years ago,<ref name="Agriodontosaurus" /> and reached worldwide distribution and peak diversity during the [[Jurassic]], when they represented the world's dominant group of small reptiles. Rhynchocephalians declined during the [[Cretaceous]], with their youngest records outside New Zealand dating to the [[Paleocene]]. Their closest living relatives are [[Squamata|squamates]] (lizards and [[snake]]s). Tuatara are of interest for studying the evolution of reptiles.

Tuatara are greenish brown and grey, and measure up to {{convert|80|cm|in|abbr=on}} from head to tail-tip and weigh up to {{convert|1.3|kg|abbr=on}}<ref name="san diego">{{cite web | title=Reptiles:Tuatara | work=Animal Bytes | publisher=Zoological Society of San Diego | year=2007 | url=http://www.sandiegozoo.org/animalbytes/t-tuatara.html | access-date=1 June 2007 | archive-url=https://web.archive.org/web/20121130133444/http://www.sandiegozoo.org/animalbytes/t-tuatara.html | archive-date=30 November 2012 }}</ref> with a spiny crest along the back, especially pronounced in males. They have two rows of teeth in the upper jaw overlapping one row on the lower jaw, which is unique among living species. They are able to hear, although no external ear is present, and have unique features in their skeleton.

Tuatara are sometimes referred to as "[[living fossil]]s".<ref name="TerraNature"/> This term is currently [[deprecated]] among paleontologists and evolutionary biologists. Although tuatara have preserved the morphological characteristics of their Mesozoic ancestors (240–230&nbsp;million years ago), there is no evidence of a continuous fossil record to support the idea that the species has survived unchanged since that time.<ref name="MeloroJones2012">{{cite journal |author1 = Meloro, C. |author2 = Jones, M.E. | title = Tooth and cranial disparity in the fossil relatives of Sphenodon (Rhynchocephalia) dispute the persistent 'living fossil' label | journal = Journal of Evolutionary Biology | volume = 25 | issue = 11 | pages = 2194–209 | date = November 2012 | pmid = 22905810 | doi = 10.1111/j.1420-9101.2012.02595.x |bibcode = 2012JEBio..25.2194M | s2cid = 32291169 | doi-access =  }}</ref><ref name="Herrera-Flores 2017">{{cite journal  |author1 = Herrera-Flores, J.A.  |author2 = Stubbs, T.L.  |author3 = Benton, M.J. |doi=10.1111/pala.12284 |title=Macroevolutionary patterns in Rhynchocephalia: is the tuatara (Sphenodon punctatus) a living fossil? |journal=Palaeontology|volume=60 |issue=3 |pages=319–328 |year=2017 |bibcode = 2017Palgy..60..319H |doi-access=free |hdl=1983/940fdc51-30db-47c0-9ac6-97fda3c2ea01 |hdl-access=free }}</ref> 

The species has between five and six billion [[base pair]]s of [[DNA sequence]], nearly twice that of humans.<ref>{{cite web |author=Elder, V. |date=26 November 2012 |work=[[Otago Daily Times]] |url=http://www.odt.co.nz/campus/university-otago/236527/tuatara-genome-mapping |title=Tuatara genome mapping |access-date=10 June 2018}}</ref>

The tuatara has been protected by law since 1895.<ref>{{Harvnb|Newman|1987}}</ref><ref>{{cite book  |author1 = Cree, A.  |author2 = Butler, D. |title=Tuatara Recovery Plan |series=Threatened Species Recovery Plan Series |volume=9 |publisher=Threatened Species Unit, Department of Conservation, Government of New Zealand |year=1993 |url=http://www.doc.govt.nz/upload/documents/science-and-technical/TSRP09.pdf |access-date=2 June 2007 |isbn=978-0-478-01462-4 | archive-url=https://web.archive.org/web/20120930212454/http://www.doc.govt.nz/upload/documents/science-and-technical/TSRP09.pdf |archive-date=30 September 2012 }}</ref> Tuatara, like many of New Zealand's native animals, are threatened by habitat loss and introduced predators, such as the [[Polynesian rat]] ''(Rattus exulans)''. Tuatara were extinct on the mainland, with the remaining populations confined to 32&nbsp;offshore islands,<ref name="DoC">{{cite web |title=Tuatara |url=http://www.doc.govt.nz/conservation/native-animals/reptiles-and-frogs/tuatara/ |archive-url=https://web.archive.org/web/20110131210804/http://www.doc.govt.nz/conservation/native-animals/reptiles-and-frogs/tuatara/ |archive-date=31 January 2011 |access-date=3 February 2013 |website=Conservation |series=Native Species |publisher=Threatened Species Unit, Department of Conservation, Government of New Zealand}}</ref> until the first North Island release into the heavily fenced and monitored [[Karori Wildlife Sanctuary]] (now named "Zealandia") in 2005.<ref name="karori">{{cite web |title=Tuatara factsheet (''Sphenodon punctatus'') |website=Sanctuary Wildlife |publisher=Karori Sanctuary Wildlife Trust |url=http://sanctuary.org.nz/restoration/forest/tuatara/tuatara-facts.html |access-date=28 June 2009 |archive-url = https://web.archive.org/web/20071021215944/http://sanctuary.org.nz/restoration/forest/tuatara/tuatara-facts.html |archive-date=21 October 2007}}</ref> During routine maintenance work at Zealandia in late 2008, a tuatara nest was uncovered,<ref name=":0">{{cite press release | url = http://www.visitzealandia.com/news-item/found-mainland-nzs-first-tuatara-nest-in-hundreds-of-years/ | archive-url = https://web.archive.org/web/20130227083004/http://www.visitzealandia.com/news-item/found-mainland-nzs-first-tuatara-nest-in-hundreds-of-years/ | archive-date = 27 February 2013 | title = New Zealand's 'living fossil' confirmed as nesting on the mainland for the first time in 200&nbsp;years! |publisher = Karori Sanctuary Trust | date = 31 October 2008 }}</ref> with a hatchling found the following autumn.<ref>{{cite press release | url = http://www.visitzealandia.com/Site/Zealandia_Home/Inside/News/Media_Releases_2009/Tuatara_baby.aspx | title = Our first baby tuatara! | publisher = Karori Sanctuary Trust | date = 18 March 2009 | access-date = 25 July 2009 | archive-date = 24 February 2023 | archive-url = https://web.archive.org/web/20230224115529/http://www.visitzealandia.com/Site/Zealandia_Home/Inside/News/Media_Releases_2009/Tuatara_baby.aspx }}</ref> This is thought to be the first case of tuatara successfully breeding in the wild on New Zealand's North Island in over 200&nbsp;years.<ref name=":0" />

==Taxonomy and evolution==
Relationships of the tuatara to other living reptiles and birds, after Simões et al. 2022<ref>{{Cite journal |last1=Simões |first1=Tiago R. |last2=Kammerer |first2=Christian F. |last3=Caldwell |first3=Michael W. |last4=Pierce |first4=Stephanie E. |date=2022-08-19 |title=Successive climate crises in the deep past drove the early evolution and radiation of reptiles |journal=Science Advances |language=en |volume=8 |issue=33 |article-number=eabq1898 |doi=10.1126/sciadv.abq1898 |issn=2375-2548 |pmc=9390993 |pmid=35984885|bibcode=2022SciA....8.1898S }}</ref>
{{clade
|label1=[[Reptilia]]
|1={{clade
|label1=[[Lepidosauria]]
|1={{clade
|1=[[Squamata]] (lizards and snakes)
|2=[[Rhynchocephalia]] (tuatara)
}}
|label2=[[Archelosauria]]
|2={{clade
|1=[[Testudines]] (turtles, including tortoises)
|label2=[[Archosauria]]
|2={{clade
|1=[[Crocodilia]] (crocodilians)
|2=[[Aves]] (birds)
}}}}}}}}

Tuatara, along with other now-extinct members of the order [[Rhynchocephalia]], belong to the superorder [[Lepidosauria]], as do the order [[Squamata]], which includes lizards and snakes. Squamates and tuatara both show [[caudal autotomy]] (loss of the tail-tip when threatened), and have transverse [[cloaca]]l slits.<ref name="encyclo">{{cite book |author=Cree, A. |title=The New Encyclopedia of Reptiles and Amphibians |publisher=Oxford University Press |year=2002 |isbn=0-19-852507-9 |editor1=Halliday, T. |place=Oxford, UK |pages=210–211 |chapter=Tuatara |editor2=Alder, K.}}</ref>

Tuatara were originally classified as lizards in 1831 when the [[British Museum]] received a skull. [[John Edward Gray]] used the name ''Sphenodon'' to describe the skull; this remains the current scientific name for the genus.<ref name="Original">{{citeQ|Q51389982|pp=13-14}}</ref><ref>{{Harvnb|Lutz|2005|p=42}}</ref> ''Sphenodon'' is derived from the [[Greek language|Greek]] for "wedge" (σφήν, σφηνός/''sphenos'') and "tooth" (ὀδούς, ὀδόντος/''odontos'').<ref>{{cite encyclopedia |title=Sphenodon |dictionary=Dictionary.com Unabridged |publisher=Random House |url=http://dictionary.reference.com/browse/sphenodon |access-date=8 January 2007 |edition=v&nbsp;1.1}}</ref> In 1842, Gray described a member of the species as ''Hatteria punctata'', not realising that it and the skull he received in 1831 were both tuatara.<ref>{{citeQ|Q51389982|pp=72}}</ref><ref Name="Gray1869">{{citeQ|Q56103814}}</ref> 

The genus remained misclassified as a lizard until 1867, when [[Albert C. L. G. Günther]] of the British Museum noted features similar to birds, turtles, and crocodiles. He proposed the order Rhynchocephalia (meaning "beak head") for the tuatara and its fossil relatives.<ref name="Günther1867">{{cite journal |author=Günther, A. |year=1867 |title=Contribution to the anatomy of ''Hatteria'' (''Rhynchocephalus'', Owen) |journal=Philosophical Transactions of the Royal Society |volume=157 |pages=595–629 |bibcode=1867RSPT..157..595G |doi=10.1098/rstl.1867.0019 |jstor=108983 |doi-access=free}}</ref> Since 1869, ''Sphenodon punctatus'' (or the variation ''Sphenodon punctatum'' in some earlier sources) has been used as the scientific name for the species.<ref name="Gray1869" />

At one point, many disparate species were incorrectly referred to the Rhynchocephalia, resulting in what taxonomists call a "[[wastebasket taxon]]".<ref name="fraser">{{cite book |title="Phylogeny" in the Shadow of the Dinosaurs: Early Mesozoic Tetrapods |publisher=Cambridge University Press |year=1994 |isbn=978-0-521-45242-7 |editor1=Fraser, N. |editor2=Sues, H.D.}}</ref> [[Samuel Wendell Williston|Williston]] in 1925 proposed the Sphenodontia to include only tuatara and their closest fossil relatives.<ref name="fraser" /> However, Rhynchocephalia is the older name<ref name="Günther1867" /> and in widespread use today. Many scholars use Sphenodontia as a subset of Rhynchocephalia, including almost all members of Rhynchocephalia, apart from the most primitive representatives of the group.<ref name=":9">{{Cite journal |last1=Sues |first1=Hans-Dieter |last2=Schoch |first2=Rainer R. |date=2023-11-07 |title=The oldest known rhynchocephalian reptile from the Middle Triassic (Ladinian) of Germany and its phylogenetic position among Lepidosauromorpha |url=https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25339 |journal=The Anatomical Record |language=en |volume=307 |issue=4 |pages=776–790 |doi=10.1002/ar.25339 |issn=1932-8486 |pmid=37937325 |url-access=subscription}}</ref>

The earliest rhynchocephalian, ''[[Agriodontosaurus]]'', is known from the [[Middle Triassic]] ([[Anisian]]) of England, around {{Ma|244|241.5}}.<ref name="Agriodontosaurus">{{Cite journal |last1=Marke |first1=Daniel |last2=Whiteside |first2=David I. |last3=Sethapanichsakul |first3=Thitiwoot |last4=Coram |first4=Robert A. |last5=Fernandez |first5=Vincent |last6=Liptak |first6=Alexander |last7=Newham |first7=Elis |last8=Benton |first8=Michael J. |author8-link=Michael Benton |date=September 10, 2025 |title=The oldest known lepidosaur and origins of lepidosaur feeding adaptations |journal=[[Nature (journal)|Nature]] |volume=647 |issue=8090 |pages=663–672 |language=en |doi=10.1038/s41586-025-09496-9 |pmid=40931068 |pmc=12629995 |bibcode=2025Natur.647..663M |issn=0028-0836 |doi-access=free}}</ref> During the [[Late Triassic]], rhynchocephalians greatly diversified,<ref name="Herrera-Flores 2017" /> going on to become the world's dominant group of small reptiles during the [[Jurassic]] period,<ref name=":20">{{Cite journal |last1=Brownstein |first1=Chase D. |last2=Meyer |first2=Dalton L. |last3=Fabbri |first3=Matteo |last4=Bhullar |first4=Bhart-Anjan S. |last5=Gauthier |first5=Jacques A. |date=2022-11-29 |title=Evolutionary origins of the prolonged extant squamate radiation |journal=Nature Communications |language=en |volume=13 |issue=1 |page=7087 |doi=10.1038/s41467-022-34217-5 |issn=2041-1723 |pmc=9708687 |pmid=36446761|bibcode=2022NatCo..13.7087B }}</ref> when the group was represented by a diversity of forms, including the aquatic [[Pleurosauridae|pleurosaurs]] and the herbivorous [[Eilenodontinae|eilenodontines]].<ref name=":20" /> The earliest members of [[Sphenodontinae]], the clade which includes the tuatara, are known from the [[Early Jurassic]] of North America. The earliest representatives of this group are already very similar to the modern tuatara.<ref name=":14">{{Cite journal |last1=Simões |first1=Tiago R. |last2=Kinney-Broderick |first2=Grace |last3=Pierce |first3=Stephanie E. |date=2022-03-03 |title=An exceptionally preserved Sphenodon-like sphenodontian reveals deep time conservation of the tuatara skeleton and ontogeny |journal=Communications Biology |language=en |volume=5 |issue=1 |page=195 |doi=10.1038/s42003-022-03144-y |issn=2399-3642 |pmc=8894340 |pmid=35241764 |doi-access=free}}</ref> Rhynchocephalians declined during the [[Cretaceous]] period,<ref>{{Cite journal |last1=Cleary |first1=Terri J. |last2=Benson |first2=Roger B. J. |last3=Evans |first3=Susan E. |last4=Barrett |first4=Paul M. |date=March 2018 |title=Lepidosaurian diversity in the Mesozoic–Palaeogene: the potential roles of sampling biases and environmental drivers |journal=Royal Society Open Science |language=en |volume=5 |issue=3 |article-number=171830 |doi=10.1098/rsos.171830 |issn=2054-5703 |pmc=5882712 |pmid=29657788|bibcode=2018RSOS....571830C }}</ref> possibly due to competition with mammals and lizards,<ref name="Jonesetal2009a" /> with their youngest record outside of New Zealand being of ''[[Kawasphenodon]]'', known from the [[Paleocene]] of Patagonia in South America.<ref name=":15">{{cite journal |vauthors=Apesteguía S, Gómez RO, Rougier GW |date=October 2014 |title=The youngest South American rhynchocephalian, a survivor of the K/Pg extinction |journal=Proceedings of the Royal Society B: Biological Sciences |volume=281 |issue=1792 |article-number=20140811 |doi=10.1098/rspb.2014.0811 |pmc=4150314 |pmid=25143041 |bibcode=2014PBioS.28140811A }}</ref>

Fossil material that can be referred to as sphenodontine is known from the [[Miocene]] [[Saint Bathans fauna]] of [[Otago]] in the South Island of New Zealand. Whether these specimens are referable to the genus ''Sphenodon'' proper is not entirely clear due to their incomplete nature, but they are likely to be from a taxon that is closely related to tuatara. Therefore, the ancestors of the tuatara were likely already present in New Zealand prior to its separation from Antarctica around 82–60 million years ago.<ref name="Jonesetal2009a">{{cite journal |vauthors=Jones ME, Tennyson AJ, Worthy JP, Evans SE, Worthy TH |date=April 2009 |title=A sphenodontine (Rhynchocephalia) from the Miocene of New Zealand and palaeobiogeography of the tuatara (Sphenodon) |journal=Proceedings. Biological Sciences |volume=276 |issue=1660 |pages=1385–90 |doi=10.1098/rspb.2008.1785 |pmc=2660973 |pmid=19203920 |bibcode=2009PBioS.276.1385J }}</ref>

Cladogram of the position of the tuatara within Sphenodontia, after Simoes et al., 2022:<ref name=":14" />{{clade|{{clade
      |1=†''[[Diphydontosaurus]]''
       |label2=Eusphenodontia
       |2={{clade
        |1=†''[[Planocephalosaurus]]''
        |2=†''[[Clevosaurus]]''
         |label3=Neosphenodontia
         |3={{clade
          |1= {{clade
           |1={{clade
|1=†''[[Homoeosaurus]]''
|label2=[[Pleurosauridae]]
|2= {{clade
|1=†''[[Palaeopleurosaurus]]''
|2= {{clade
|1=†''[[Derasmosaurus]]''
|2= †''[[Pleurosaurus]]''
}}}}
 |3={{clade
  |1={{clade
|1=†''[[Leptosaurus]]''
|2=†''[[Kallimodon]]''
}}
|label2=[[Sapheosauridae]]
  |2={{clade
|1=†''[[Piocormus]]''
|2=†''[[Oenosaurus]]''
|3=†''[[Sapheosaurus]]''
}}
}}
}}
          |label2=[[Sphenodontidae]]
          |2={{clade
          |label1=[[Eilenodontinae]]
          |label2=[[Sphenodontinae]]
            |1={{clade
|1=†''[[Sphenotitan]]''
|2={{clade
|1=†''[[Eilenodon]]''
|2={{clade
|1=†''[[Toxolophosaurus]]''
|2=†''[[Priosphenodon]]''
}}}}}}
            |2={{clade
             |1=†''[[Navajosphenodon]]''
             |2=†''[[Cynosphenodon]]''
             |3={{clade
               |1=†''[[Sphenofontis]]''
               |2={{clade
                  |1=†''[[Kawasphenodon]]''
                  |2='''''Sphenodon''''' (tuatara)
    }}}}}}}}}}}}}}}}|label1=[[Sphenodontia]]}}

===Species===
While there is currently considered to be only one living species of tuatara, two species were previously identified: ''Sphenodon punctatus'', or northern tuatara, and the much rarer ''Sphenodon guntheri'', or Brothers Island tuatara, which is confined to [[The Brothers (New Zealand)|North Brother Island]] in [[Cook Strait]].<ref name="BBC">{{cite web |title=Tuatara – ''Sphenodon punctatus'' |url=http://www.bbc.co.uk/nature/wildfacts/factfiles/3052.shtml |archive-url=https://web.archive.org/web/20050828031645/http://www.bbc.co.uk/nature/wildfacts/factfiles/3052.shtml |archive-date=28 August 2005 |access-date=28 February 2006 |website=Science and Nature: Animals |publisher=[[BBC]] (bbc.co.uk)}}</ref> The [[Specific name (zoology)|specific name]] ''punctatus'' is [[latin language|Latin]] for "spotted",<ref>{{cite book |author=Stearn, W.T. |url=https://books.google.com/books?id=w0hZvTFJUioC&q=botanical+epithets+punctatus&pg=PA476 |title=Botanical Latin |date=1 April 2004 |publisher=Timber Press |isbn=978-0-88192-627-9 |place=Portland, OR |page=476 |via=Google Books}}</ref> and ''guntheri'' refers to [[Germany|German]]-born [[British people|British]] [[Herpetology|herpetologist]] [[Albert Günther]].<ref>{{cite book |author1=Beolens, Bo |author1-link=species:Bo Beolens |title=The Eponym Dictionary of Reptiles |author2=Watkins, Michael |author2-link=species:Michael Watkins |author3=Grayson, Michael |publisher=Johns Hopkins University Press |year=2011 |isbn=978-1-4214-0135-5 |place=Baltimore, Maryland }} xiii + 296 pp. (''Sphenodon guntheri'', p. 110).</ref> A 2009 paper re-examined the genetic bases used to distinguish the two supposed species of tuatara, and concluded they represent only geographic variants, and only one species should be recognised.<ref name="Hay">{{cite journal |vauthors=Hay JM, Sarre SD, Lambert DM, Allendorf FW, Daugherty CH |year=2010 |title=Genetic diversity and taxonomy: a reassessment of species designation in tuatara (''Sphenodon'': Reptilia) |url=https://link.springer.com/article/10.1007/s10592-009-9952-7 |journal=Conservation Genetics |volume=11 |pages=1063–1081 |bibcode=2010ConG...11.1063H |doi=10.1007/s10592-009-9952-7 |s2cid=24965201 |hdl-access=free |number=3 |hdl=10072/30480|url-access=subscription }}</ref> Consequently, the northern tuatara was re-classified as ''Sphenodon punctatus punctatus'' and the Brothers Island tuatara as ''Sphenodon punctatus guntheri''. The Brothers Island tuatara has olive brown skin with yellowish patches, while the colour of the northern tuatara ranges from olive green through grey to dark pink or brick red, often mottled, and always with white spots.<ref name="karori" /><ref name="encyclo" /><ref name="lutz16">{{Harvnb|Lutz|2005|p=16}}</ref> In addition, the Brothers Island tuatara is considerably smaller.<ref name="NZRG">{{cite book |author1=Gill, B. |title=New Zealand Frogs and Reptiles |author2=Whitaker, T. |publisher=David Bateman Publishing |year=1996 |isbn=1-86953-264-3 |pages=22–24}}</ref> However, individuals from Brothers Island could not be distinguished from other modern and fossil samples on the basis of jaw morphology.<ref name="Vaux 2019">{{cite journal |author1=Vaux, F. |author2=Morgan-Richards, M. |author3=Daly, E.E. |author4=Trewick, S.A. |year=2019 |title=Tuatara and a new morphometric dataset for Rhynchocephalia: Comments on Herrera-Flores ''et al''. |url=https://onlinelibrary.wiley.com/doi/10.1111/pala.12402 |journal=Palaeontology |volume=62 |issue=2 |pages=321–334 |bibcode=2019Palgy..62..321V |doi=10.1111/pala.12402 |s2cid=134902015|url-access=subscription }}</ref> 

An extinct species of ''Sphenodon'' was identified in November&nbsp;1885 by William Colenso, who was sent an incomplete [[subfossil]] specimen from a local coal mine. Colenso named the new species ''S. diversum''.<ref name="colenso1885">{{cite journal |author=Colenso, W. |year=1885 |title=Notes on the bones of a species of ''Sphenodon'', (''S. diversum'', Col.,) apparently distinct from the species already known |url=http://rsnz.natlib.govt.nz/volume/rsnz_18/rsnz_18_00_000850.pdf |journal=Transactions and Proceedings of the Royal Society of New Zealand |volume=18 |pages=118–128}}</ref> Fawcett and Smith (1970) consider it a synonym to the subspecies, based on a lack of distinction.<ref>{{Cite journal |last1=Fawcett |first1=James D. |last2=Smith |first2=Hobart M. |date=1970 |title=An Overlooked Synonym of Sphenodon punctatus, the New Zealand Tuatara |journal=Journal of Herpetology |volume=4 |issue=1–2 |pages=89–91|doi=10.2307/1562712 |jstor=1562712 }}</ref>

==Description==
[[File:Tuatara scale.png|thumb|left|upright|Size comparison of male ''S.&nbsp;punctatus'' and human]]
[[File:Sphenodon punctatus LH288.jpg|thumb|Skeleton of the tuatara]]

Tuatara are the largest reptiles in New Zealand.<ref>{{Cite web |title=Tuatara |url=https://www.doc.govt.nz/nature/native-animals/reptiles-and-frogs/tuatara/ |access-date=2022-12-12 |website=[[Department of Conservation (New Zealand)|Department of Conservation]] |language=en-nz}}</ref> Adult ''S.&nbsp;punctatus'' males measure {{convert|61|cm|in|abbr=on}} in length and females {{convert|45|cm|in|abbr=on}}.<ref name="encyclo" /> Tuatara are [[sexual dimorphism|sexually dimorphic]], males being larger.<ref name="encyclo" /> The [[San Diego Zoo]] even cites a length of up to {{convert|80|cm|in|abbr=on}}.<ref>{{cite web |publisher=[[San Diego Zoo]] |series=Animal Bytes |title=Tuatara |url=http://www.sandiegozoo.org/animalbytes/t-tuatara.html |archive-url=https://web.archive.org/web/20121130133444/http://www.sandiegozoo.org/animalbytes/t-tuatara.html |archive-date=30 November 2012 |access-date=19 April 2008}}</ref> Males weigh up to {{convert|1|kg|lb|abbr=on}}, and females up to {{convert|0.5|kg|lb|abbr=on}}.<ref name="encyclo" /> Brothers Island tuatara are slightly smaller, weighing up to 660&nbsp;g (1.3&nbsp;lb).<ref name="NZRG" />

Their lungs have a single chamber with no [[bronchi]].<ref>{{cite book |author=Jacobson, E.R. |date=2007-04-11 |title=Infectious Diseases and Pathology of Reptiles |publisher=CRC Press |isbn=978-1-4200-0403-8 |url=https://books.google.com/books?id=hhO4WAZcVLEC&pg=PA13}}</ref>

The tuatara's greenish brown colour matches its environment, and can change over its lifetime. Tuatara shed their skin at least once per year as adults,<ref name="lutz16" /> and three or four times a year as juveniles. Tuatara sexes differ in more than size. The spiny crest on a tuatara's back, made of triangular, soft folds of skin, is larger in males, and can be stiffened for display. The male abdomen is narrower than the female's.<ref>{{cite web |title=Tuataras |website=Animal Corner |url=http://www.animalcorner.co.uk/reptiles/rep_tuatara.html |archive-url=https://web.archive.org/web/20150317073012/http://animalcorner.co.uk/reptiles/rep_tuatara.html |archive-date=17 March 2015 |access-date=31 December 2007}}</ref>

===Skull===
[[File:Tuatara skull diagram.svg|thumb|Skull diagram in top down and side-on views]]
Unlike the vast majority of lizards, the tuatara has a complete lower temporal bar closing the lower [[temporal fenestra]] (an opening of the skull behind the eye socket), caused by the fusion of the [[Quadrate bone|quadrate]]/[[Quadratojugal bone|quadratojugal]] (which are fused into a single element in adult tuatara) and the [[jugal bone]]s of the skull. This is similar to the condition found in primitive [[diapsid]] reptiles. However, because more primitive rhynchocephalians have an open lower temporal fenestra with an incomplete temporal bar, this is thought to be a [[Derived (phylogenetics)|derived]] characteristic of the tuatara and other members of the clade [[Sphenodontinae]], rather than a primitive trait retained from early diapsids. The complete bar is thought to stabilise the skull during biting.<ref name=":14" />

The tip of the upper jaw is chisel- or beak-like and separated from the remainder of the jaw by a notch,<ref name="Günther1867" /> this structure is formed from fused [[premaxilla]]ry teeth, and is also found in many other advanced rhynchocephalians.<ref>{{Cite journal |last1=Herrera-Flores |first1=Jorge A. |last2=Stubbs |first2=Thomas L. |last3=Elsler |first3=Armin |last4=Benton |first4=Michael J. |date=July 2018 |title=Taxonomic reassessment of Clevosaurus latidens Fraser, 1993 (Lepidosauria, Rhynchocephalia) and rhynchocephalian phylogeny based on parsimony and Bayesian inference |journal=Journal of Paleontology |language=en |volume=92 |issue=4 |pages=734–742 |doi=10.1017/jpa.2017.136 |issn=0022-3360|doi-access=free |bibcode=2018JPal...92..734H |hdl=1983/59126b60-16d8-46d2-b657-954693a39d4e |hdl-access=free }}</ref> The teeth of the tuatara, and almost all other rhynchocephalians, are described as [[acrodont]], as they are attached to the apex of the jaw bone. This contrast with the [[pleurodont]] condition found in the vast majority of lizards, where the teeth are attached to the inward-facing surface of the jaw. The teeth of the tuatara are extensively fused to the jawbone, making the boundary between the tooth and jaw difficult to discern, and the teeth lack roots and are not replaced during the lifetime of the animal, unlike those of pleurodont lizards.<ref>{{Cite journal |last1=Jenkins |first1=Kelsey M. |last2=Jones |first2=Marc E. H. |last3=Zikmund |first3=Tomas |last4=Boyde |first4=Alan |last5=Daza |first5=Juan D. |date=September 2017 |title=A Review of Tooth Implantation Among Rhynchocephalians (Lepidosauria) |url=http://www.bioone.org/doi/10.1670/16-146 |journal=Journal of Herpetology |language=en |volume=51 |issue=3 |pages=300–306 |doi=10.1670/16-146 |issn=0022-1511 |s2cid=90519352|url-access=subscription }}</ref> It is a common misconception that tuatara lack teeth and instead have sharp projections on the jaw bone;<ref name="lutzp27">{{Harvnb|Lutz|2005|p=27}}</ref> histology shows that they have true teeth with enamel and dentine with pulp cavities.<ref name="Kieser2009">{{cite journal |vauthors=Kieser JA, Tkatchenko T, Dean MC, Jones ME, Duncan W, Nelson NJ |year=2009 |title=Microstructure of dental hard tissues and bone in the Tuatara dentary, ''Sphenodon punctatus'' (Diapsida: Lepidosauria: Rhynchocephalia) |url=https://www.karger.com/Article/Abstract/242396 |journal=Frontiers of Oral Biology |volume=13 |pages=80–85 |doi=10.1159/000242396 |isbn=978-3-8055-9229-1 |pmid=19828975|url-access=subscription }}</ref> As their teeth wear down, older tuatara have to switch to softer prey, such as [[earthworm]]s, [[larva]]e, and [[slug]]s, and eventually have to chew their food between smooth jaw bones.<ref>{{cite news |author=Mlot, C. |date=8 November 1997 |title=Return of the Tuatara: A relic from the age of dinosaurs gets a human assist |website=Science News |url=http://www.sciencenews.org/pages/pdfs/data/1997/152-19/15219-21.pdf |access-date=24 May 2007}}</ref>

The tuatara possesses palatal dentition (teeth growing from the bones of the roof of the mouth), which is ancestrally present in reptiles (and [[tetrapod]]s generally).<ref name=":13">{{cite journal |vauthors=Matsumoto R, Evans SE |date=January 2017 |title=The palatal dentition of tetrapods and its functional significance |journal=[[Journal of Anatomy]] |volume=230 |issue=1 |pages=47–65 |doi=10.1111/joa.12534 |pmc=5192890 |pmid=27542892}}</ref> While many of the original palatal teeth present in reptiles have been lost,<ref name=":13" /> as in all other known rhynchocephalians, the row of teeth growing from the [[palatine bone]]s in the tuatara have been enlarged, and as in other members of Sphenodontinae the palatine teeth are orientated parallel to the teeth in the [[maxilla]]; during biting the teeth of the lower jaw slot between the two upper tooth rows.<ref name="Jones2008">{{cite journal |author=Jones, M.E. |date=August 2008 |title=Skull shape and feeding strategy in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria) |journal=Journal of Morphology |volume=269 |issue=8 |pages=945–66 |doi=10.1002/jmor.10634 |pmid=18512698 |bibcode=2008JMorp.269..945J |s2cid=16357353 |doi-access=free}}</ref> The structure of the jaw joint allows the lower jaw to slide forwards after it has closed between the two upper rows of teeth.<ref name="Jones et al. 2012">{{cite journal |vauthors=Jones ME, O'higgins P, Fagan MJ, Evans SE, Curtis N |date=July 2012 |title=Shearing mechanics and the influence of a flexible symphysis during oral food processing in Sphenodon (Lepidosauria: Rhynchocephalia) |journal=The Anatomical Record |volume=295 |issue=7 |pages=1075–91 |doi=10.1002/ar.22487 |pmid=22644955 |s2cid=45065504|doi-access=free }}</ref> This mechanism allows the jaws to shear through [[chitin]] and bone.<ref name="encyclo" />

The brain of ''Sphenodon'' fills only half of the volume of its [[endocranium]].<ref name="larsson2001">{{cite book |vauthors=Larsson HC |year=2001 |chapter=Endocranial anatomy of ''Carcharodontosaurus saharicus'' (Theropoda: Allosauroidea) and its implications for theropod brain evolution |veditors=Tanke DH, Carpenter K, Skrepnick MW |title=Mesozoic Vertebrate Life |place=Bloomington & Indianapolis |publisher=Indiana University Press |isbn=0-253-33907-3 |pages=19–33}}</ref> This proportion has been used by paleontologists trying to estimate the volume of dinosaur brains based on fossils.<ref name="larsson2001" /> However, the proportion of the tuatara endocranium occupied by its brain may not be a very good guide to the same proportion in Mesozoic dinosaurs since modern birds are surviving dinosaurs but have brains which occupy a much greater relative volume in the endocranium.<ref name="larsson2001" />

{{gallery|Tuatara Skull Lateral (50669113641).jpg|Skull of the tuatara in oblique view|File:Sphenodon punctatus (AM LH288) 601767.jpg|Skull of the tuatara in oblique view, with [[sclerotic ring]]s in eye sockets|Sphenodon punctatus (AM LH288) 601763 (cropped).jpg|Skull of tuatara from above|File:Tuatara Skull Doral (50668366013).jpg|Skull of tuatara from above|Tuatara skull diagram.jpg|Tuatara skull in various views with palatine tooth row visible on underside of the skull|||||||width=200|height=180|lines=|align=center}}

===Sensory organs===
[[File:Tuatara (7714490358).jpg|thumb|left|Close-up of a tuatara's head]]

==== Eyes ====
The eyes can [[Accommodation (eye)|focus]] independently, and are specialised with three types of photoreceptive cells, all with fine structural characteristics of retinal [[cone cell]]s<ref>{{cite journal |vauthors=Meyer-Rochow VB, Wohlfahrt S, Ahnelt PK |year=2005 |title=Photoreceptor cell types in the retina of the tuatara (Sphenodon punctatus) have cone characteristics |url=https://www.sciencedirect.com/science/article/abs/pii/S0968432805000521 |journal=Micron |volume=36 |issue=5 |pages=423–428 |doi=10.1016/j.micron.2005.03.009 |pmid=15896966|url-access=subscription }}</ref> used for both day and night vision, and a ''[[tapetum lucidum]]'' which reflects onto the retina to enhance vision in the dark. There is also a third eyelid on each eye, the [[nictitating membrane]]. Five visual [[opsin]] genes are present, suggesting good [[colour vision]], possibly even at low light levels.<ref name="Gemmell2020">{{cite journal |vauthors=Gemmell NJ, Rutherford K, Prost S, Tollis M, Winter D, Macey JR, Adelson DL, Suh A, Bertozzi T, Grau JH, Organ C, Gardner PP, Muffato M, Patricio M, Billis K, Martin FJ, Flicek P, Petersen B, Kang L, Michalak P, Buckley TR, Wilson M, Cheng Y, Miller H, Schott RK, Jordan MD, Newcomb RD, Arroyo JI, Valenzuela N, Hore TA, Renart J, Peona V, Peart CR, Warmuth VM, Zeng L, Kortschak RD, Raison JM, Zapata VV, Wu Z, Santesmasses D, Mariotti M, Guigó R, Rupp SM, Twort VG, Dussex N, Taylor H, Abe H, Bond DM, Paterson JM, Mulcahy DG, Gonzalez VL, Barbieri CG, DeMeo DP, Pabinger S, Van Stijn T, Clarke S, Ryder O, Edwards SV, Salzberg SL, Anderson L, Nelson N, Stone C |date=August 2020 |title=The tuatara genome reveals ancient features of amniote evolution |journal=Nature |volume=584 |issue=7821 |pages=403–409 |doi=10.1038/s41586-020-2561-9 |pmc=7116210 |pmid=32760000 |bibcode=2020Natur.584..403G |doi-access=free}}</ref>

==== Parietal eye (third eye) ====
Like some other living vertebrates, including some lizards, the tuatara has a third eye on the top of its head called the [[parietal eye]] (also called a pineal or third eye) formed by the parapineal organ, with an accompanying opening in the skull roof called the pineal or parietal foramen, enclosed by the [[parietal bone]]s.<ref name=":1">{{Cite journal |last1=Smith |first1=Krister T. |last2=Bhullar |first2=Bhart-Anjan S. |last3=Köhler |first3=Gunther |last4=Habersetzer |first4=Jörg |date=April 2018 |title=The Only Known Jawed Vertebrate with Four Eyes and the Bauplan of the Pineal Complex |journal=Current Biology |volume=28 |issue=7 |pages=1101–1107.e2 |doi=10.1016/j.cub.2018.02.021 |issn=0960-9822|doi-access=free |pmid=29614279 |bibcode=2018CBio...28E1101S }}</ref> It has its own lens, a parietal plug which resembles a [[cornea]],<ref>{{cite journal |author1=Schwab, I.R. |author2=O'Connor, G.R. |date=March 2005 |title=The lonely eye |journal=The British Journal of Ophthalmology |volume=89 |issue=3 |page=256 |doi=10.1136/bjo.2004.059105 |pmc=1772576 |pmid=15751188}}</ref> [[retina]] with rod-like structures, and degenerated nerve connection to the brain. The parietal eye is visible only in hatchlings, which have a translucent patch at the top centre of the skull. After four to six months, it becomes covered with opaque scales and pigment.<ref name="encyclo" /> While capable of detecting light, it is probably not capable of detecting movement or forming an image.<ref>{{Cite journal |last1=Jones |first1=Marc E.H. |last2=Cree |first2=Alison |date=December 2012 |title=Tuatara |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982212013036 |journal=Current Biology |language=en |volume=22 |issue=23 |pages=R986–R987 |doi=10.1016/j.cub.2012.10.049|pmid=23218010 |bibcode=2012CBio...22.R986J |url-access=subscription }}</ref> It likely serves to regulate the [[circadian rhythm]] and possibly detect seasonal changes, and help with [[thermoregulation]].<ref name="encyclo" /><ref name=":1" />

Of all extant tetrapods, the parietal eye is most pronounced in the tuatara. It is part of the pineal complex, another part of which is the [[pineal gland]], which in tuatara secretes melatonin at night.<ref name="encyclo" /> Some [[salamander]]s have been shown to use their pineal bodies to perceive polarised light, and thus determine the position of the sun, even under cloud cover, aiding [[Animal navigation|navigation]].<ref>{{cite book |author=Halliday, T.R. |year=2002 |chapter=Salamanders and newts: Finding breeding ponds |editor1=Halliday, T. |editor2=Adler, K. |title=The New Encyclopedia of Reptiles and Amphibians |place=Oxford, UK |publisher=Oxford University Press |isbn=0-19-852507-9|page=52}}</ref>

==== Hearing ====
Together with [[turtle]]s, the tuatara has the most primitive hearing organs among the amniotes. There is no tympanum ([[eardrum]]) and no earhole,<ref name="lutzp27" /> and the [[middle ear]] cavity is filled with loose tissue, mostly [[adipose tissue]] (fat). The [[stapes]] comes into contact with the [[Quadrate bone|quadrate]] (which is immovable), as well as the [[hyoid]] and [[squamosal]]. The [[hair cell]]s are unspecialised, innervated by both [[Afferent nerve|afferent]] and [[efferent nerve]] fibres, and respond only to low frequencies. Though the hearing organs are poorly developed and primitive with no visible external ears, they can still show a frequency response from 100 to 800&nbsp;[[Hertz|Hz]], with peak sensitivity of 40&nbsp;[[Decibel|dB]] at 200&nbsp;Hz.<ref>{{cite web |author=Kaplan, Melissa |date=6 September 2003 |title=Reptile Hearing |website=Melissa Kaplan's herp care collection |url=http://www.anapsid.org/reptilehearing.html |access-date=24 July 2006}}</ref>

==== Odorant receptors ====
Animals that depend on the sense of smell to capture prey, escape from predators or simply interact with the environment they inhabit, usually have many odorant receptors. These receptors are expressed in the dendritic membranes of the neurons for the detection of odours. The tuatara has around 472 receptors, a number more similar to what birds have than to the large number of receptors that turtles and crocodiles may have.<ref name="Gemmell2020" />

===Spine and ribs===
The tuatara [[Vertebral column|spine]] is made up of hourglass-shaped [[Vertebral column#Classification|amphicoelous]] vertebrae, concave both before and behind.<ref name="lutzp27" /> This is the usual condition of fish vertebrae and some amphibians, but is unique to tuatara within the amniotes. The vertebral bodies have a tiny hole through which a constricted remnant of the notochord passes; this was typical in early fossil reptiles, but lost in most other amniotes.<ref>{{cite book |author1=Romer, A.S. |author2=Parsons, T.S. |year=1977 |title=The Vertebrate Body |edition=Fifth |location=Philadelphia, PA |publisher=W.B. Saunders |isbn=978-0-7216-7668-5 |page=624}}</ref>

The tuatara has [[gastralia]], rib-like bones also called gastric or abdominal ribs,<ref>{{cite web |title=Tuatara |website=Berlin Zoo Aquarium |url=http://www.aquarium-berlin.de/en/experience/animal-highlights/tuatara.html |access-date=11 September 2007 |archive-url=https://web.archive.org/web/20070814075005/http://www.aquarium-berlin.de/en/experience/animal-highlights/tuatara.html <!--Added by H3llBot--> |archive-date=14 August 2007}}</ref> the presumed ancestral trait of diapsids. They are found in some [[lizard]]s, where they are mostly made of cartilage, as well as crocodiles and the tuatara, and are not attached to the spine or thoracic ribs. The true ribs are small projections, with small, hooked bones, called uncinate processes, found on the rear of each rib.<ref name="lutzp27" /> This feature is also present in birds. The tuatara is the only living [[tetrapod]] with well-developed gastralia and uncinate processes.

In the early tetrapods, the gastralia and ribs with uncinate processes, together with bony elements such as bony plates in the skin (osteoderms) and [[clavicle]]s (collar bone), would have formed a sort of exoskeleton around the body, protecting the belly and helping to hold in the guts and inner organs. These anatomical details most likely evolved from structures involved in locomotion even before the vertebrates ventured onto land. The gastralia may have been involved in the breathing process in early amphibians and reptiles. The pelvis and shoulder girdles are arranged differently from those of lizards, as is the case with other parts of the internal anatomy and its scales.<ref>{{cite web |author=Wattie, T. |website=www.kiwizone.org |title=Tuatara Reptile, New Zealand |url=http://nzphoto.tripod.com/animal/tuatara.htm |access-date=31 December 2007 |archive-url=https://web.archive.org/web/20071114212222/http://nzphoto.tripod.com/animal/tuatara.htm |archive-date=14 November 2007}}</ref>

===Tail and back===
The spiny plates on the back and tail of the tuatara resemble those of a crocodile more than a lizard, but the tuatara shares with lizards the ability to break off its tail when caught by a predator, and then regenerate it. The regrowth takes a long time and differs from that of lizards. Well illustrated reports on tail regeneration in tuatara have been published by Alibardi and Meyer-Rochow.<ref>{{cite journal |author1=Alibardi, L. |author2=Meyer-Rochow, V.B. |year=1990 |title=Ultrastructural survey of the spinal cord of young tuatara (''Sphenodon punctatus'') with emphasis on the glia |journal=New Zealand Journal of Zoology |volume=17 |pages=73–85 |doi=10.1080/03014223.1990.10422586}}</ref><ref>{{cite journal |author1=Alibardi, L. |author2=Meyer-Rochow, V.B. |year=1990 |title=Fine structure of regenerating caudal spinal cord in adult tuatara (''Sphenodon punctatus'') |journal=Journal für Hirnforschung |volume=31 |issue=5 |pages=613–21 |pmid=1707076}}</ref> The cloacal glands of tuatara have a unique [[organic compound]] named [[tuataric acid]].

=== Age determination ===
Currently, there are two means of determining the age of tuatara. Using microscopic inspection, hematoxylinophilic rings can be identified and counted in both the phalanges and the femur. Phalangeal hematoxylinophilic rings can be used for tuatara up to ages 12–14&nbsp;years, as they cease to form around this age. Femoral rings follow a similar trend, however they are useful for tuatara up to ages 25–35&nbsp;years. Around that age, femoral rings cease to form.<ref>{{cite journal |author1=Castanet, J. |author2=Newman, D.G. |author3=Girons, H.S. |date=1988 |title=Skeletochronological data on the growth, age, and population structure of the tuatara, ''Sphenodon punctatus'', on Stephens and Lady Alice Islands, New Zealand |journal=Herpetologica |volume=44 |issue=1 |pages=25–37 |jstor=3892195}}</ref> Further research on age determination methods for tuatara is required, as tuatara have lifespans much longer than 35&nbsp;years (ages up to 60<ref name="KCC" /> are common, and captive tuatara have lived to over 100&nbsp;years).<ref name="Disc-Mag-2009-01-26" /><ref name="NZHer-2009-01-26" /><ref name="BBCNews-2009-01-26" /> One possibility could be via examination of tooth wear, as tuatara have fused sets of teeth.

=== Physiology ===
[[File:TWC Wildlife Centre• Stewart Nimmo • MRD 8910.jpg|thumb|left|A tuatara basking at the West Coast Wildlife Centre, at [[Franz Josef / Waiau|Franz Josef]] on the [[West Coast, New Zealand|West Coast]]]]

Adult tuatara are [[Landform|terrestrial]] and [[nocturnal]] reptiles, though they will often bask in the sun to warm their bodies. Hatchlings hide under logs and stones, and are [[Diurnality|diurnal]], likely because adults are cannibalistic. Juveniles are typically active at night, but can be found active during the day. The juveniles' movement pattern is attributed to genetic hardwire of conspecifics for predator avoidance and thermal restrictions.<ref>{{Cite journal |last1=Terezow |first1=Marianna G. |last2=Nelson |first2=Nicola J. |last3=Markwell |first3=Timothy J. |date=January 2008 |title=Circadian emergence and movement of captive juvenile tuatara (''Sphenodon''spp.) |journal=New Zealand Journal of Zoology |volume=35 |issue=3 |pages=205–216 |doi=10.1080/03014220809510116 |issn=0301-4223 |s2cid=83781111|doi-access=free }}</ref> Tuatara thrive in temperatures much lower than those tolerated by most reptiles, and [[hibernation|hibernate]] during winter.<ref>{{cite web |date=18 January 2006 |title=Tuatara: Facts |url=http://www.southlandmuseum.com/tuatara_-_facts.htm |archive-url=https://web.archive.org/web/20070609034405/http://www.southlandmuseum.com/tuatara_-_facts.htm |archive-date=9 June 2007 |access-date=2 June 2007 |publisher=Southland Museum}}</ref> They remain active at temperatures as low as {{convert|5|°C|°F|0}},<ref>{{cite news |author=Schofield, E. |date=24 March 2009 |title=New arrivals thrill staff at sanctuary |newspaper=[[Otago Daily Times]] |place=Otago, NZ |url=http://www.odt.co.nz/your-town/dunedin/48665/new-arrivals-thrill-staff-sanctuary |access-date=23 March 2009}}</ref> while temperatures over {{convert|28|°C|°F|0}} are generally fatal. The optimal body temperature for the tuatara is from {{convert|16|to|21|C|F}}, the lowest of any reptile.<ref name="UofM">{{cite web |author=Musico, B. |year=1999 |title=''Sphenodon punctatus'' |url=http://animaldiversity.ummz.umich.edu/site/accounts/information/Sphenodon_punctatus.html |access-date=22 April 2006 |website=Animal Diversity Web |publisher=University of Michigan Museum of Zoology}}</ref> The body temperature of tuatara is lower than that of other reptiles, ranging from {{convert|5.2|-|11.2|C|F}} over a day, whereas most reptiles have body temperatures around {{convert|20|°C|°F|0}}.<ref>{{cite journal |author1=Thompson, M.B. |author2=Daugherty, C.H. |year=1998 |title=Metabolism of tuatara, ''Sphenodon punctatus'' |journal=Comparative Biochemistry and Physiology A |volume=119 |issue=2 |pages=519–522 |doi=10.1016/S1095-6433(97)00459-5}}</ref> The low body temperature results in a slower [[metabolism]].{{Clear}}

== Ecology ==

Burrowing seabirds such as [[petrel]]s, [[prion (bird)|prions]], and [[shearwater]]s share the tuatara's island habitat during the birds' nesting seasons. The tuatara use the [[bird]]s' burrows for shelter when available, or dig their own. The seabirds' [[guano]] helps to maintain invertebrate populations on which tuatara predominantly prey, including [[beetle]]s, [[crickets]], [[spider]]s, [[wētā]]s, [[earthworm]]s, and [[snail]]s.<ref name="Sphenodon punctatus Tuatara">{{cite web | url=https://animaldiversity.org/accounts/Sphenodon_punctatus/ | title=Sphenodon punctatus (Tuatara) | website=[[Animal Diversity Web]] }}</ref> Their diets also consist of [[frog]]s, [[lizard]]s, and bird's eggs and chicks.<ref name="Vaux 2019" /> Young tuatara are also occasionally cannibalised.<ref name="Sphenodon punctatus Tuatara" /> The diet of the tuatara varies seasonally, and they consume mainly [[fairy prions]] and their eggs in the summer.<ref>{{Cite thesis |title=Diets of wild tuatara (Sphenodon punctatus) on Stephens Island |url=https://ourarchive.otago.ac.nz/handle/10523/2959 |publisher=University of Otago |date=1993 |degree=Thesis |language=en |first=James |last=Fraser}}</ref>  In total darkness no feeding attempt was observed,<ref>{{cite journal |author = Meyer-Rochow, V.B. |year=1988 |title=Behaviour of young tuatara (''Sphenodon punctatus'') in total darkness |journal=Tuatara |volume=30 |pages=36–38}}</ref> and the lowest light intensity at which an attempt to snatch a beetle was observed occurred under 0.0125&nbsp;[[lux (unit)|lux]].<ref>{{cite journal |last1=Meyer-Rochow |first1=Victor Benno |last2=Teh |first2=Katrina L. |date=July 1991 |title=Visual Predation by Tuatara (Sphenodon Punctatus) on the Beach Beetle (Chaerodes Trachyscelides) as a Selective force in the Production of Distinct Colour Morphs |url=https://nzetc.victoria.ac.nz/tm/scholarly/name-102493.html |journal=Tuatara: Journal of the Biological Society |volume=31 |issue=1 |pages=1–8 |via=[[Victoria University of Wellington]]}}</ref> The eggs and young of seabirds that are seasonally available as food for tuatara may provide [[essential fatty acid|beneficial fatty acids]].<ref name="encyclo" /> Tuatara of both sexes defend territories, and will threaten and eventually bite intruders. The bite can cause serious injury.<ref>{{cite encyclopedia |author1 = Daugherty, C. |author2 = Keall, S. |title = Tuatara: Life History |encyclopedia = Te Ara – the Encyclopedia of New Zealand  |url = https://teara.govt.nz/en/tuatara/page-1}}</ref> Tuatara will bite when approached, and will not let go easily.<ref name="lutz24">{{Harvnb|Lutz|2005|p=24}}</ref> Female tuatara sometimes exhibit parental behaviour by guarding nests from other females.<ref>{{cite journal |last1=Refsnider |first1=Jeanine M. |last2=Keall |first2=Susan N. |last3=Daugherty |first3=Charles H. |last4=Nelson |first4=Nicola J. |title=Does Nest-Guarding in Female Tuatara (Sphenodon punctatus) Reduce Nest Destruction by Conspecific Females? |journal=Journal of Herpetology |date=2009 |volume=43 |issue=2 |pages=294–299 |doi=10.1670/08-120R1.1 }}</ref>

Tuatara are parasitised by the [[tuatara tick]] (''Archaeocroton sphenodonti''), a [[tick]] that directly depends on tuatara.<ref name="godf">{{cite journal |last1=Godfrey |first1=S. S. |last2=Bull |first2=C. M. |last3=Nelson |first3=N. J. |title=Seasonal and spatial dynamics of ectoparasite infestation of a threatened reptile, the tuatara (''Sphenodon punctatus'') |journal=Medical and Veterinary Entomology |date=2008 |volume=22 |issue=4 |pages=374–385 |doi=10.1111/j.1365-2915.2008.00751.x|pmid=19120965 |s2cid=20718129 }}</ref> These ticks tend to be more prevalent on larger males, as they have larger home ranges than smaller and female tuatara and interact with other tuatara more in territorial displays.<ref>{{cite journal |last1=Godfrey |first1=Stephanie |last2=Moore |first2=Jennifer |last3=Nelson |first3=Nicola |last4=Bull |first4=Michael |title=Social network structure and parasite infection patterns in a territorial reptile, the tuatara (Sphenodon punctatus) |journal=International Journal for Parasitology |date=2010 |volume=40 |issue=13 |pages=1575–1585 |doi=10.1016/j.ijpara.2010.06.002 |pmid=20637210 }}</ref>

==Reproduction==
{{Multiple image
| direction         = vertical
| align             = left
| image1            = Henry at Invercargill.jpg
| caption1          = A male tuatara named Henry, living at the [[Southland Museum and Art Gallery]], is still reproductively active at 111&nbsp;years of age.<ref name=Disc-Mag-2009-01-26>{{cite news |title=111&nbsp;year-old reptile becomes a dad after tumor surgery |date = 26 January 2009 |magazine=[[Discover Magazine]] |url=http://blogs.discovermagazine.com/discoblog/2009/01/26/111-year-old-reptile-becomes-a-dad-after-tumor-surgery/ |access-date=2013-01-31 |archive-url=https://web.archive.org/web/20121015183849/http://blogs.discovermagazine.com/discoblog/2009/01/26/111-year-old-reptile-becomes-a-dad-after-tumor-surgery/ |archive-date=15 October 2012}}</ref>
| image2            = Brueckenechse.jpg
| caption2          = Tuatara juvenile (''Sphenodon punctatus'')
}}

Tuatara reproduce very slowly, taking 10 to 20&nbsp;years to reach sexual maturity.<ref>{{cite news |author = Angier, N. |date = 22 November 2010 |title = Reptile's pet-store looks belie its Triassic appeal |newspaper = [[The New York Times]] |url = https://www.nytimes.com/2010/11/23/science/23angier.html?pagewanted=1&_r=2&hpw |access-date =21 December 2010}}</ref> Though their reproduction rate is slow, tuatara have the fastest swimming sperm by two to four times compared to all reptiles studied earlier.<ref>{{Cite web |last1=Ormsby |first1=Diane Karen |last2=Moore |first2=Jennifer |last3=Nelson |first3=Nicola Jane |last4=Lamar |first4=Sarah K. |last5=Keall |first5=Susan N. |title=Tuatara are ancient, slow and endangered. But their super speedy sperm could boost conservation efforts |url=http://theconversation.com/tuatara-are-ancient-slow-and-endangered-but-their-super-speedy-sperm-could-boost-conservation-efforts-165173 |access-date=2022-12-12 |website=The Conversation |date=3 August 2021 |language=en}}</ref> Mating occurs in midsummer; females mate and lay [[Egg (biology)|egg]]s once every four years.<ref>{{cite journal |author1=Cree, A. |author2=Cockrem, J.F. |author3=Guillette, L.J. |year = 1992 |title = Reproductive cycles of male and female tuatara (''Sphenodon punctatus'') on Stephens Island, New Zealand |journal = Journal of Zoology |volume = 226 |issue = 2  |pages = 199–217 |doi = 10.1111/j.1469-7998.1992.tb03834.x |bibcode=1992JZoo..226..199C }}</ref> During courtship, a male makes his skin darker, raises his crests, and parades toward the female. He slowly walks in circles around the female with stiffened legs. The female will either allow the male to mount her, or retreat to her burrow.<ref>{{cite journal |author1= Gans, C. |author2=Gillingham, J.C. |author3=Clark, D.L. | year = 1984 | title = Courtship, mating and male combat in Tuatara, ''Sphenodon punctatus'' | journal = Journal of Herpetology | volume = 18 | issue=2 | pages = 194–197 | doi=10.2307/1563749 | jstor=1563749}}</ref> Adult males do not have a penis or any form of intromittent phallus.<ref>{{cite journal |vauthors=Sanger TJ, Gredler ML, Cohn MJ |date=October 2015 |title=Resurrecting embryos of the tuatara, Sphenodon punctatus, to resolve vertebrate phallus evolution |journal=[[Biology Letters]] |volume=11 |issue=10 |article-number=20150694 |doi=10.1098/rsbl.2015.0694 |pmc=4650183 |pmid=26510679}}</ref> They reproduce by the male lifting the tail of the female and placing his [[cloaca|vent]] (cloaca) over hers. This process is sometimes referred to as a "cloacal kiss". The [[sperm]] is then transferred into the female, much like the mating process in birds.<ref>{{Harvnb|Lutz|2005|p=19}}</ref> Along with birds, the tuatara is one of the few members of [[Amniote|Amniota]] to have lost the ancestral penis.<ref>{{cite journal | author = Brennan, P.L. | date = January 2016 | title = Evolution: One penis after all | journal = Current Biology | volume = 26 | issue = 1 | pages = R29-31 | pmid = 26766229 | doi = 10.1016/j.cub.2015.11.024 | doi-access = free | bibcode = 2016CBio...26..R29B }}</ref>

Tuatara eggs have a soft, parchment-like 0.2mm thick shell that consists of calcite crystals embedded in a matrix of fibrous layers.<ref>{{cite journal |author1 = Packard, M.J. |author2 = Hirsch, K.F. |author3 = Meyer-Rochow, V.B. |date = November 1982 |title = Structure of the shell from eggs of the tuatara, ''Sphenodon punctatus'' |journal = Journal of Morphology |volume = 174 |issue = 2 |pages = 197–205 | pmid = 30096972 |doi = 10.1002/jmor.1051740208 |bibcode = 1982JMorp.174..197P |s2cid = 51957289 }}</ref> It takes the females between one and three years to provide eggs with yolk, and up to seven months to form the shell. It then takes between 12 and 15&nbsp;months from copulation to hatching. This means reproduction occurs at two- to five-year intervals, the slowest in any reptile.<ref name="encyclo" />

Some females guard their eggs for up to 10 days. Rather than predators, the primary threat to unhatched offspring seems to be posed by unrelated female tuatara. While looking for a place to lay their own eggs, they can destroy a previous brood present in the nest. Eggs protected by their mother from rival females appear to have higher chance of survival.<ref>{{Cite journal |last=Refsnider, Jaenine & Keall, Susan & Daugherty, Charles & Nelson, Nicola |date=2009 |title=Does Nest-Guarding in Female Tuatara (Sphenodon punctatus) Reduce Nest Destruction by Conspecific Females? |journal=Journal of Herpetology |volume=43 |issue=2 |pages=294–298 |doi=10.1670/08-120R1.1}}</ref>

Survival of embryos has also been linked to having more success in moist conditions.<ref>{{Cite journal |last1=Thompson |first1=M. B. |last2=Packard |first2=G. C. |last3=Packard |first3=M. J. |last4=Rose |first4=B. |date=February 1996 |title=Analysis of the nest environment of tuatara Sphenodon punctatus |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1996.tb05392.x |journal=Journal of Zoology |language=en |volume=238 |issue=2 |pages=239–251 |doi=10.1111/j.1469-7998.1996.tb05392.x |bibcode=1996JZoo..238..239T |issn=0952-8369|url-access=subscription }}</ref> Wild tuatara are known to be still reproducing at about 60&nbsp;years of age; "[[Henry (tuatara)|Henry]]", a male tuatara at [[Southland Museum and Art Gallery|Southland Museum]] in [[Invercargill]], New Zealand, became a father (possibly for the first time) on 23&nbsp;January 2009, at age&nbsp;111, with an 80&nbsp;year-old female.<ref name="NZHer-2009-01-26">{{cite news |title=Tuatara becomes a father for the first time, aged&nbsp;111 |newspaper=[[The New Zealand Herald]] |date=26 January 2009 |url=http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10553616 |access-date=28 June 2009}}</ref><ref name="BBCNews-2009-01-26">{{cite news |title=Reptile becomes a father, at 111 |date=26 January 2009 |website=[[BBC News]] |url=https://news.bbc.co.uk/2/hi/asia-pacific/7850975.stm |access-date=28 June 2009}}</ref><ref name="Disc-Mag-2009-01-26" />

The sex of a hatchling [[Temperature-dependent sex determination|depends on the temperature]] of the egg, with warmer eggs tending to produce male tuatara, and cooler eggs producing females. Eggs incubated at {{convert|21|°C|°F|0}} have an equal chance of being male or female. However, at {{convert|22|°C|°F|0}}, 80% are likely to be males, and at {{convert|20|°C|°F|0}}, 80% are likely to be females; at {{convert|18|°C|°F|0}} all hatchlings will be females.<ref name="KCC" /> Some evidence indicates sex determination in tuatara is determined by both genetic and environmental factors.<ref>{{cite journal |author1 = Cree, A. |author2 = Thompson, M.B. |author3 = Daugherty, C.H. |year = 1995 |title = Tuatara sex determination |journal = Nature |volume = 375 |issue = 6532 |page = 543 |doi = 10.1038/375543a0 |doi-access = free |bibcode=1995Natur.375..543C |s2cid=4339729}}</ref>

Tuatara probably have the slowest growth rates of any reptile,<ref name="encyclo" /> continuing to grow larger for the first 35&nbsp;years of their lives.<ref name="KCC" /> The average lifespan is about 60 years, but they can live to be well over 100 years old;<ref name="KCC" /> tuatara could be the reptile with the second longest lifespan after tortoises.{{Citation needed|date=December 2020}} Some experts believe that captive tuatara could live as long as 200 years.<ref name="CNNDad">{{cite news |title=110&nbsp;year-old 'living fossil' becomes a dad |date=30 January 2009 |website =[[CNN]] |url=http://www.cnn.com/2009/TECH/science/01/29/lizard.reproduces/index.html |access-date=28 June 2009}}</ref> This may be related to genes that offer protection against reactive oxygen species.{{explain|date=June 2023|reason=what are 'reactive oxygen species'?}} The tuatara genome has 26&nbsp;genes that encode [[selenoprotein]]s and 4&nbsp;[[selenocysteine]]-specific [[tRNA]] genes. In humans, selenoproteins have a function of antioxidation, redox regulation and synthesis of thyroid hormones. It is not fully demonstrated, but these genes may be related to the longevity of this animal or may have emerged as a result of the low levels of selenium and other trace elements in the New Zealand terrestrial systems.<ref name="Gemmell2020" />

== Genomic characteristics ==
The most abundant [[Long interspersed nuclear element|LINE element]] in the tuatara is L2 (10%). Most of them are interspersed and can remain active. The longest L2 element found is 4 kb long and 83% of the sequences had ORF2p completely intact. The CR1 element is the second most repeated (4%). Phylogenetic analysis shows that these sequences are very different from those found in other nearby species such as lizards. Finally, less than 1% are elements belonging to L1, a low percentage since these elements tend to predominate in placental mammals.<ref name="Gemmell2020" /> Usually, the predominant LINE elements are the CR1, contrary to what has been seen in the tuatara. This suggests that perhaps the genome repeats of sauropsids were very different compared to mammals, birds and lizards.<ref name="Gemmell2020" />

The genes of the [[major histocompatibility complex]] (MHC) are known to play roles in disease resistance, [[mate choice]], and kin recognition in various vertebrate species. Among known vertebrate genomes, MHCs are considered one of the most polymorphic.<ref>{{cite journal |author=Sommer, S. |date=October 2005 |title=The importance of immune gene variability (MHC) in evolutionary ecology and conservation |journal=Frontiers in Zoology |volume=2 |issue=1 |article-number=16 |doi=10.1186/1742-9994-2-16 |pmc=1282567 |pmid=16242022 |doi-access=free}}</ref><ref>{{cite journal |vauthors=Rymešová D, Králová T, Promerová M, Bryja J, Tomášek O, Svobodová J, Šmilauer P, Šálek M, Albrecht T |date=2017-02-16 |title=Mate choice for major histocompatibility complex complementarity in a strictly monogamous bird, the grey partridge (''Perdix perdix'') |journal=Frontiers in Zoology |volume=14 |article-number=9 |doi=10.1186/s12983-017-0194-0 |pmc=5312559 |pmid=28239400 |doi-access=free}}</ref> In the tuatara, 56 MHC genes have been identified; some of which are similar to MHCs of amphibians and mammals. Most MHCs that were annotated in the tuatara genome are highly conserved, however there is large genomic rearrangement observed in distant [[lepidosaur]] lineages.<ref name="Gemmell2020" />

Many of the elements that have been analyzed are present in all [[amniote]]s, most are mammalian interspersed repeats or MIR, specifically the diversity of MIR subfamilies is the highest that has been studied so far in an amniote. 16&nbsp;families of [[Short interspersed nuclear element|SINEs]] that were recently active have also been identified.<ref name="Gemmell2020" />

The tuatara has 24&nbsp;unique families of [[DNA transposon]]s, and at least 30 subfamilies were recently active. This diversity is greater than what has been found in other amniotes and in addition, thousands of identical copies of these transposons have been analyzed, suggesting to researchers that there is recent activity.<ref name="Gemmell2020" />

The genome is the second largest known to reptiles. Only the [[Greek tortoise]] genome is larger.<ref>{{cite journal | last1=Alam | first1=S. M. | last2=Sarre | first2=S. D. | last3=Gleeson | first3=D. | last4=Georges | first4=A. | last5=Ezaz | first5=T. | title=Did Lizards Follow Unique Pathways in Sex Chromosome Evolution? | journal=Genes | date=2018 | volume=9 | issue=5 | page=239 | doi=10.3390/genes9050239 | doi-access=free | pmid=29751579 | pmc=5977179 }}</ref> Around 7,500&nbsp;[[LTR retrotransposon|LTRs]] have been identified, including 450&nbsp;[[endogenous retrovirus]]es (ERVs). Studies in other [[Sauropsida]] have recognised a similar number but nevertheless, in the genome of the tuatara it has been found a very old clade of retrovirus known as [[Spumavirus]].<ref name="Gemmell2020" />

More than 8,000&nbsp;[[non-coding RNA]]-related elements have been identified in the tuatara genome, of which the vast majority, about 6,900, are derived from recently active [[transposable element]]s. The rest are related to ribosomal, [[Spliceosome|spliceosomal]] and [[signal recognition particle RNA]].<ref name="Gemmell2020" />

The [[Mitochondrial DNA|mitochondrial genome]] of the genus ''Sphenodon'' is approximately 18,000&nbsp;bp in size and consists of 13&nbsp;protein-coding genes, 2&nbsp;[[ribosomal RNA]] and 22&nbsp;[[transfer RNA]] genes.<ref name="Gemmell2020" />

[[DNA methylation]] is a very common modification in animals and the distribution of [[CpG site]]s within genomes affects this methylation. Specifically, 81% of these CpG sites have been found to be methylated in the tuatara genome. Recent publications propose that this high level of methylation may be due to the amount of repeating elements that exist in the genome of this animal. This pattern is closer to what occurs in organisms such as zebrafish, about 78%, while in humans it is only 70%.<ref name="Gemmell2020" />

==Conservation==
Tuatara are absolutely protected under New Zealand's [[Wildlife Act 1953]].<ref>{{cite web |title=Wildlife Act 1953 |url=https://www.legislation.govt.nz/act/public/1953/0031/latest/whole.html |website=New Zealand Legislation |publisher=Parliamentary Counsel Office |access-date=18 January 2022}}</ref> The species is also listed under Appendix&nbsp;I of the [[Convention on International Trade in Endangered Species]] (CITES) meaning commercial international trade in wild sourced specimens is prohibited and all other international trade (including in parts and derivatives) is regulated by the CITES permit system.<ref>{{cite web |title=Appendices |website=CITES (cites.org) |publisher=[[Convention on International Trade in Endangered Species]] |url=https://cites.org/eng/app/appendices.php |access-date=2022-01-14}}</ref>
[[File:Tuatara, Nelson, NZ imported from iNaturalist photo 450639255.jpg|thumb|Tuatara sighted on the [[South Island]] mainland, in November 2024.]]

===Distribution and threats===
Tuatara were once widespread on New Zealand's main North and South Islands, where [[subfossil]] remains have been found in sand dunes, caves, and Māori [[midden]]s.<ref>{{cite journal |author1 = Towns, D.R. |author2 = Daugherty, C.H. |author3 = Cree, A. |title=Raising the prospects for a forgotten fauna: A review of 10&nbsp;years of conservation effort for New Zealand reptiles |journal=Biological Conservation |year=2001 |volume=99 |issue = 1 |pages=3–16 |doi=10.1016/s0006-3207(00)00184-1 |bibcode = 2001BCons..99....3T |url=http://www.claudius-r-us.com/forum/download/file.php?id=77 |access-date=11 March 2012|archive-url=https://web.archive.org/web/20140424131734/http://www.claudius-r-us.com/forum/download/file.php?id=77 |archive-date=24 April 2014|url-access=subscription }}</ref> Wiped out from the main islands before European settlement, they were long confined to 32&nbsp;offshore islands free of mammals.<ref name="DoC"/> The islands are difficult to get to,<ref>{{Harvnb|Lutz|2005|pp=59–60}}</ref> and are colonised by few animal species, indicating that some animals absent from these islands may have caused tuatara to disappear from the mainland. However, ''kiore'' (Polynesian rats) had recently become established on several of the islands, and tuatara were persisting, but not breeding, on these islands.<ref>{{cite journal |author=Crook, I.G. |year=1973 |title=The tuatara, ''Sphenodon punctatus'' {{small|(Gray)}}, on islands with and without populations of the Polynesian rat, ''Rattus exulans'' {{small|(Peale)}} |journal=Proceedings of the New Zealand Ecological Society |volume=20 |pages=115–120 |jstor=24061518 }}</ref><ref name=cree_etal1995>{{cite journal |author1 = Cree, A. |author2 = Daugherty, C.H. |author3 = Hay, J.M. |year = 1995 |title = Reproduction of a rare New Zealand reptile, the tuatara ''Sphenodon punctatus'', on rat-free and rat-inhabited islands |journal = Conservation Biology |volume = 9 |issue = 2 |pages = 373–383 |doi = 10.1046/j.1523-1739.1995.9020373.x|bibcode = 1995ConBi...9..373C }}</ref> Additionally, tuatara were much rarer on the rat-inhabited islands.<ref name=cree_etal1995/> Prior to conservation work, 25% of the distinct tuatara populations had become extinct in the past century.<ref name = "Daugherty_1990">{{cite journal |author1 = Cree, A. |author2 = Daugherty, C.H. |author3 = Hay, J.M. |date=1990-09-01 |title=Neglected taxonomy and continuing extinctions of tuatara (''Sphenodon'') |journal=Nature |volume=347 |issue=6289 |pages=177–179 |doi=10.1038/347177a0 |bibcode=1990Natur.347..177D |s2cid=4342765}}</ref>

The recent discovery of a tuatara hatchling on the mainland indicates that attempts to re-establish a breeding population on the New Zealand mainland have had some success.<ref name=bergner>{{cite news |title=Rare reptile hatchling found in New Zealand |newspaper=[[The Guardian]] |date=20 March 2009 |url=https://www.theguardian.com/environment/2009/mar/20/tuatara-reptile-new-zealand }}</ref> The total population of tuatara is estimated to be between 60,000<ref name=encyclo /> and 100,000.<ref>{{cite encyclopedia |author1 = Daugherty, C. |author2 = Keall, S. |title = Tuatara islands |encyclopedia = Te Ara – the Encyclopedia of New Zealand |url = http://www.teara.govt.nz/TheBush/FishFrogsAndReptiles/Tuatara/2/en |access-date = 10 September 2008 |archive-date = 10 April 2023 |archive-url = https://web.archive.org/web/20230410162516/https://teara.govt.nz/TheBush/FishFrogsAndReptiles/Tuatara/2/en }}</ref>

==== Climate change ====
Tuatara have temperature-dependent sex determination meaning that the temperature of the egg determines the sex of the animal. For tuatara, lower egg incubation temperatures lead to females while higher temperatures lead to males. Since global temperatures are increasing, climate change may be skewing the male to female ratio of tuatara. Current solutions to this potential future threat are the selective removal of adults and the incubation of eggs.<ref>{{Cite web |date=2017-02-06 |title=A Threat to New Zealand's Tuatara Heats Up |url=https://www.americanscientist.org/article/a-threat-to-new-zealands-tuatara-heats-up |access-date=2022-12-12 |website=American Scientist |language=en}}</ref><ref>{{cite journal |last1=Hoare |first1=J. M. |last2=Pledger |first2=S. |last3=Keall |first3=S. N. |last4=Nelson |first4=N. J. |last5=Mitchell |first5=N. J. |last6=Daugherty |first6=C. H. |title=Conservation implications of a long-term decline in body condition of the Brothers Island tuatara ( Sphenodon guntheri ) |journal=Animal Conservation |date=November 2006 |volume=9 |issue=4 |pages=456–462 |doi=10.1111/j.1469-1795.2006.00061.x|bibcode=2006AnCon...9..456H |s2cid=86412390 }}</ref>

===Eradication of rats===
Tuatara were removed from [[Stanley Island, New Zealand|Stanley]], [[Red Mercury Island|Red Mercury]] and [[Cuvier Island]]s in 1990 and 1991, and maintained in captivity to allow Polynesian rats to be eradicated on those islands. All three populations bred in captivity, and after successful eradication of the rats, all individuals, including the new juveniles, were returned to their islands of origin. In the 1991–92 season, [[Little Barrier Island]] was found to hold only eight tuatara, which were taken into ''[[in situ conservation|in situ]]'' captivity, where females produced 42 eggs, which were incubated at Victoria University. The resulting offspring were subsequently held in an enclosure on the island, then released into the wild in 2006 after rats were eradicated there.<ref>{{cite report |title=Fauna on Little Barrier Island |department=Department of Conservation |publisher=Government of New Zealand |url=http://www.doc.govt.nz/parks-and-recreation/places-to-visit/auckland/hauraki-gulf-islands/little-barrier-island-nature-reserve-hauturu-o-toi/features/#fauna |access-date=3 February 2013 |archive-url=https://web.archive.org/web/20140329040539/http://www.doc.govt.nz/parks-and-recreation/places-to-visit/auckland/hauraki-gulf-islands/little-barrier-island-nature-reserve-hauturu-o-toi/features/#fauna |archive-date=29 March 2014}}</ref>

In the [[Hen and Chicken Islands]], Polynesian rats were eradicated on Whatupuke in 1993, Lady Alice Island in 1994, and Coppermine Island in 1997. Following this program, juveniles have once again been seen on the latter three islands. In contrast, rats persist on Hen Island of the same group, and no juvenile tuatara have been seen there as of 2001. In the [[Alderman Islands]], Middle Chain Island holds no tuatara, but it is considered possible for rats to swim between Middle Chain and other islands that do hold tuatara, and the rats were eradicated in 1992 to prevent this.<ref name=recovery/> Another rodent eradication was carried out on the Rangitoto Islands east of [[D'Urville Island]], to prepare for the release of 432&nbsp;Cook Strait tuatara juveniles in 2004, which were being raised at Victoria University as of 2001.<ref name=recovery /><!--can we find out whether this plan was followed through?-->

====Brothers Island tuatara====
''Sphenodon punctatus guntheri'' is present naturally on one small island with a population of approximately 400. In 1995, 50&nbsp;juvenile and 18&nbsp;adult Brothers Island tuatara were moved to Titi Island in [[Cook Strait]], and their establishment monitored. Two years later, more than half of the animals had been seen again and of those all but one had gained weight. In 1998, 34&nbsp;juveniles from captive breeding and 20&nbsp;wild-caught adults were similarly transferred to [[Matiu/Somes Island]], a more publicly accessible location in Wellington Harbour. The captive juveniles were from induced layings from wild females.<ref name=recovery />

In late October&nbsp;2007, 50&nbsp;tuatara collected as eggs from North Brother Island and hatched at [[Victoria University of Wellington|Victoria University]] were being released onto [[Long Island, Marlborough|Long Island]] in the outer [[Marlborough Sounds]]. The animals had been cared for at Wellington Zoo for the previous five years and had been kept in secret in a specially built enclosure at the zoo, off display.<ref>{{cite press release | title = Rare tuatara raised at Wellington Zoo | publisher = [[Wellington Zoo]] | date = 29 October 2007 | url = http://www.scoop.co.nz/stories/SC0710/S00061.htm |access-date =19 April 2008}}</ref>

There is another out of country population of Brothers Island tuatara that was given to the [[San Diego Zoological Society]] and is housed off-display at the [[San Diego Zoo]] facility in Balboa.<ref>{{cite news |series=Reptiles |title=Tuatara |department=At the Zoo |publisher = San Diego Zoo Wildlife Alliance |url=http://animals.sandiegozoo.org/animals/tuatara |access-date=11 May 2014}}</ref> No successful reproductive efforts have been reported yet.

====Northern tuatara====
[[File:Tuatara karori head.jpg|thumb|upright|Tuatara at the [[Karori Wildlife Sanctuary|Karori Sanctuary]] are given coloured markings on the head for identification.]]
''S.&nbsp;punctatus punctatus'' naturally occurs on 29&nbsp;islands, and its population is estimated to be over 60,000&nbsp;individuals.<ref name=encyclo/> In 1996, 32&nbsp;adult northern tuatara were moved from [[Moutoki Island]] to [[Moutohora Island|Moutohora]]. The carrying capacity of Moutohora is estimated at 8,500&nbsp;individuals, and the island could allow public viewing of wild tuatara.<ref name=recovery/> In 2003, 60&nbsp;northern tuatara were introduced to [[Tiritiri Matangi Island]] from Middle Island in the [[Mercury Islands|Mercury group]]. They are occasionally seen sunbathing by visitors to the island.<ref>{{cite web | url = http://www.doc.govt.nz/upload/documents/getting-involved/students-and-teachers/field-trips-by-region/tiri-education-kit/15-part-4-reptiles-167-174.pdf | title = Translocated reptiles |volume = Part 4: Reptiles | work = Tiritiri Matangi: An education resource for schools | publisher = Department of Conservation, Government of New Zealand }}</ref><ref>{{cite web | title = Tiritiri Matangi Island field trip | url = http://www.doc.govt.nz/getting-involved/for-teachers/field-trip-resources/field-trips-by-region/auckland/tiritiri-matangi-island/teaching-resource/ | work = Tiritiri Matangi – An education resource for schools | archive-url = https://web.archive.org/web/20140329033704/http://www.doc.govt.nz/getting-involved/for-teachers/field-trip-resources/field-trips-by-region/auckland/tiritiri-matangi-island/teaching-resource/ | archive-date = 29 March 2014 | publisher = Department of Conservation, Government of New Zealand | date = November 2007}}</ref>

A mainland release of ''S.p.&nbsp;punctatus'' occurred in 2005 in the heavily fenced and monitored [[Karori Wildlife Sanctuary|Karori Sanctuary]].<ref name="karori"/> The second mainland release took place in October&nbsp;2007, when a further 130 were transferred from [[Stephens Island, New Zealand|Stephens Island]] to the Karori Sanctuary.<ref>{{cite news |title=130&nbsp;tuatara find sanctuary |date=20 October 2007 |newspaper=[[The Dominion Post (Wellington)|The Dominion Post]] |place=Wellington, NZ |url=http://www.stuff.co.nz/stuff/4243952a7693.html |access-date=19 April 2008 |archive-url=https://web.archive.org/web/20081210145408/https://www.stuff.co.nz/stuff/4243952a7693.html |archive-date=10 December 2008}}</ref> In early 2009, the first recorded wild-born offspring were observed.<ref>{{cite news |author = Easton, P. |date=20 March 2009  |title=Life will be wild for new boy |newspaper=[[The Dominion Post (Wellington)|The Dominion Post]] |place=Wellington, NZ |url=http://www.stuff.co.nz/environment/2278328/Life-will-be-wild-for-new-boy/ |access-date=20 March 2009 |archive-url=https://web.archive.org/web/20090614014223/http://www.stuff.co.nz/environment/2278328/Life-will-be-wild-for-new-boy/ |archive-date = 14 June 2009}}</ref>

===Captive breeding===
{{more citations needed section|date=November 2022}}
The first successful breeding of tuatara in captivity is believed to have achieved by Sir [[Algernon Thomas]] at either his University offices or residence in Symonds Street in the late 1880s or his new home, Trewithiel, in Mount Eden in the early 1890s.{{citation needed|date=February 2022}}

Several tuatara breeding programmes are active in New Zealand. [[southland museum and art gallery|Southland Museum and Art Gallery]] in [[Invercargill]] was the first institution to have a tuatara breeding programme; starting in 1986 they bred ''S.&nbsp;punctatus'' and have focused on ''S.&nbsp;guntheri'' more recently.<ref>{{cite book |last1=Lutz |first1=Richard L. |title=Tuatara: a living fossil |date=2006 |publisher=Dimi Press |location=Salem, OR |page=53 |url=https://worldcat.org/en/title/57434219 |access-date=22 November 2022}}</ref>

[[Hamilton Zoo]], [[Auckland Zoo]] and [[Wellington Zoo]] also breed tuatara for release into the wild. At Auckland Zoo in the 1990s it was discovered that tuatara have [[temperature-dependent sex determination]].
The [[Victoria University of Wellington]] maintains a research programme into the captive breeding of tuatara, and the [[Pūkaha / Mount Bruce National Wildlife Centre]] keeps a pair and a juvenile.{{citation needed|date=February 2022}}

The WildNZ Trust has a tuatara breeding enclosure at [[Ruawai]]. One notable captive breeding success story took place in January&nbsp;2009, when all 11 eggs belonging to 110&nbsp;year-old tuatara [[Henry (tuatara)|Henry]] and 80&nbsp;year-old tuatara Mildred hatched. This story is especially remarkable as Henry required surgery to remove a cancerous tumour in order to successfully breed.<ref name="CNNDad"/>

In January 2016, [[Chester Zoo]], England, announced that they succeeded in breeding the tuatara in captivity for the first time outside its homeland.<ref>{{cite news |author = Connor, S. |date=31 January 2016 |title=Tuatara: Lizard-like reptile takes 38&nbsp;years to lay an egg in Chester Zoo |newspaper=[[The Independent]] |url=https://www.independent.co.uk/environment/nature/tuatura-lizard-like-reptile-takes-38-years-to-lay-an-egg-in-chester-zoo-a6844041.html |access-date=31 January 2016}}</ref>

==Cultural significance==
Tuatara feature in a number of indigenous legends, and are held as ''ariki'' (God forms). Tuatara are regarded as the messengers of [[Whiro]], the [[deity|god]] of death and disaster, and Māori women are forbidden to eat them.<ref>{{cite web |author = Williams, D. |title =Chapter 6: Traditional Kaitiakitanga Rights and Responsibilities |work =Wai 262 Report: Matauranga Maori and Taonga| publisher =Waitangi Tribunal |year =2001 |url =http://www.waitangi-tribunal.govt.nz/doclibrary/public/wai262/matauranga_maori/Chapt06.pdf |access-date=2 June 2007 |archive-url =https://web.archive.org/web/20070628044808/http://www.waitangi-tribunal.govt.nz/doclibrary/public/wai262/matauranga_maori/Chapt06.pdf |archive-date =28 June 2007}}</ref> Tuatara also indicate ''tapu'' (the borders of what is sacred and restricted),<ref name="ramdstad">{{cite journal |vauthors=Ramstad KM, Nelson NJ, Paine G, Beech D, Paul A, Paul P, Allendorf FW, Daugherty CH |date=April 2007 |title=Species and cultural conservation in New Zealand: maori traditional ecological knowledge of tuatara |url=https://conbio.onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.2006.00620.x |journal=Conservation Biology |volume=21 |issue=2 |pages=455–64 |doi=10.1111/j.1523-1739.2006.00620.x |pmid=17391195 |bibcode=2007ConBi..21..455R |s2cid=39213356|url-access=subscription }}</ref> beyond which there is ''mana'', meaning there could be serious consequences if that boundary is crossed.<ref name=ramdstad /> Māori women would sometimes tattoo images of lizards, some of which may represent tuatara, near their genitals.<ref name=ramdstad /> Today, tuatara are regarded as a ''[[taonga]]'' (special treasure) along with being viewed as the [[kaitiaki]] (guardian) of knowledge.<ref>{{Harvnb|Lutz|2005|p=64}}</ref><ref>{{Cite web |last=Taonga |first=New Zealand Ministry for Culture and Heritage Te Manatu |title=Life history |url=https://teara.govt.nz/en/tuatara/page-1 |access-date=2022-12-12 |website=[[Te Ara: The Encyclopedia of New Zealand]] |language=en}}</ref>

The tuatara was featured on one side of the [[New Zealand five-cent coin]], which was phased out in October 2006. ''Tuatara'' was also the name of the ''Journal of the Biological Society'' of Victoria University College and subsequently [[Victoria University of Wellington]], published from 1947 until 1993. It has now been digitised by the [[New Zealand Electronic Text Centre]], also at Victoria.<ref>{{cite web |title=Tuatara: Journal of the Biological Society |publisher=New Zealand Electronic Text Centre |place=Wellington, NZ |url=https://nzetc.victoria.ac.nz/tm/scholarly/tei-corpus-tuatara.html |access-date=19 April 2008}}</ref>
[[File:Tuatara, 1316498 (cropped).jpg|thumb|center|Photograph taken for Life Magazine by [[Arthur Breckon]] ,1937]]

==Notes==
{{notes}}

== References ==
{{reflist}}

== Further reading ==
{{Refbegin|30em}}
* {{cite book | vauthors = Blanchard B | collaboration = Tuatara Recovery Group | veditors = Jasperse J, Rolfe J |url = http://www.doc.govt.nz/upload/documents/science-and-technical/TSOP21.pdf | title = Tuatara captive management plan and husbandry manual | series = Threatened Species Occasional Publication | volume = 21 | publisher = Department of Conservation | location = Wellington, New Zealand | access-date =26 November 2007 |date = June 2002 }}
* {{cite web | vauthors = Bry L | title=Evolution of a third eye in some animals? | work = MadSci Network | url=http://www.madsci.org/posts/archives/2005-07/1121008231.Zo.r.html | access-date=9 August 2007}}
* {{cite encyclopedia | vauthors = Daugherty C, Keall S | url = http://www.teara.govt.nz/TheBush/FishFrogsAndReptiles/Tuatara/en | title = Tuatara | encyclopedia = Te Ara – the Encyclopedia of New Zealand | archive-url = https://web.archive.org/web/20081015051223/http://www.teara.govt.nz/TheBush/FishFrogsAndReptiles/Tuatara/en | archive-date = 15 October 2008 }}
* {{cite journal | vauthors = Daugherty CH, Cree A | title = Tuatara: a survivor from the dinosaur age. | journal = New Zealand Geographic | date = April 1990 | volume = 6 | pages = 66–86 }}
* {{cite web | vauthors = Gill V | date = 30 May 2012 | url = http://www.bbc.co.uk/nature/18249270 | title = Tuatara reptile slices food with 'steak-knife teeth | work = BBC Nature | archive-url = https://web.archive.org/web/20170826011404/http://www.bbc.co.uk/nature/18249270 | access-date = 8 January 2014 | archive-date = 26 August 2017 }}
* {{cite book| vauthors = Lutz D | year = 2005| title = Tuatara: A Living Fossil| location = Salem, Oregon | publisher = Dimi Press | isbn = 978-0-931625-43-5}}
* {{cite web | vauthors = Maisano J | url=http://digimorph.org/specimens/Sphenodon_punctatus/adult/ | work = Digimorph | publisher = University of Texas at Austin | title= ''Sphenodon punctatus'' (tuatara) – 3D visualisations from X-ray CT scans | access-date=8 May 2006}}
* {{cite web | vauthors = Marris J | work = ARKive: Images of Life on Earth | title = Images and movies of the Brothers Island tuatara ''(Sphenodon guntheri)'' | url=http://www.arkive.org/species/GES/reptiles/Sphenodon_guntheri/ | access-date=3 June 2007 | archive-url=https://web.archive.org/web/20070626014815/http://www.arkive.org/species/GES/reptiles/Sphenodon_guntheri/ | archive-date=26 June 2007 }}
* {{cite book | vauthors = McKintyre M | year=1997 | title=Conservation of the Tuatara | publisher=Victoria University Press | isbn=978-0-86473-303-0 }}
* {{cite web | vauthors = Mulligan J | title = Tuatara | publisher = [[Radio New Zealand|RNZ]] | work = Critter of the Week | url = http://www.radionz.co.nz/national/programmes/afternoons/audio/201855296/critter-of-the-week-the-tuatara | date = 18 August 2017 }}
* {{cite book| vauthors = Newman DG | year = 1987| title = Tuatara. Endangered New Zealand Wildlife Series| publisher = Dunedin, New Zealand: John McIndoe| isbn = 978-0-86868-098-9}}
* {{cite book | vauthors = Parkinson B | year=2000 | title=The Tuatara | publisher=Reed Children's Books | isbn=978-1-86948-831-4}}
* {{cite journal | vauthors = Schwab IR, O'Connor GR | title = The lonely eye | journal = The British Journal of Ophthalmology | volume = 89 | issue = 3 | page = 256 | date = March 2005 | pmid = 15751188 | pmc = 1772576 | doi = 10.1136/bjo.2004.059105 }}
{{Refend}}

== External links ==
* {{cite web |url=http://collections.tepapa.govt.nz/Taxon.aspx?irn=7307 |title=Specimens of ''Tuatara'' |publisher=The collection of the Museum of New Zealand |location=Te Papa Tongarewa |access-date=17 July 2010 |archive-date=22 May 2010 |archive-url=https://web.archive.org/web/20100522111410/http://collections.tepapa.govt.nz/Taxon.aspx?irn=7307 }}

{{Portal bar|Reptiles|Evolutionary biology|New Zealand}}
{{Rhynchocephalia|state=autocollapse}}
{{New Zealand Reptiles}}
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[[Category:Endemic reptiles of New Zealand]]
[[Category:Extant Late Pleistocene first appearances]]
[[Category:Māori culture]]
[[Category:Rhynchocephalia]]
[[Category:Taxa named by John Edward Gray]]