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{{Short description|Order of reptiles}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
{{Distinguish|Rhynchosaur}}
{{Automatic taxobox
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'''Rhynchocephalia''' ({{IPAc-en|,|r|I|N|k|ou|s|ᵻ|'|f|ei|l|i|@}}; {{lit|beak-heads}}) is an [[order (biology)|order]] of lizard-like [[reptile]]s that includes only one living species, the [[tuatara]] (''Sphenodon punctatus'') of [[New Zealand]]. Despite its current lack of diversity, during the [[Mesozoic]] rhynchocephalians were a speciose group with high morphological and ecological diversity. The oldest record of the group is dated to the [[Middle Triassic]] around 238 to 240 million years ago, and they had achieved
== History ==
[[Tuatara]] were originally classified as [[Agamidae|agamid]] [[lizard]]s when they were first described by [[John Edward Gray]] in 1831. They remained misclassified until 1867, when [[Albert C. L. G. Günther|Albert 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=":6" /> In 1925, [[Samuel Wendell Williston]] proposed the Sphenodontia to include only tuatara and their closest fossil relatives.<ref name="fraser">{{cite book |title="Phylogeny" In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods |publisher=[[Cambridge University Press]] |year=1994 |isbn=0-521-45242-2 |veditors=Fraser N, Sues HD}}</ref> ''Sphenodon'' is derived from [[Ancient Greek|Greek]] {{lang|el|σφήν}} {{transliteration|el|sphen}} 'wedge' and {{lang|el|ὀδούς}} {{transliteration|el|odous}} 'tooth'.<ref name="Evansetal01">{{cite journal |vauthors=Evans SE, Prasad GV, Manhas BK |author1-link=Susan E. Evans |title=Rhynchocephalians (Diapsida: Lepidosauria) from the Jurassic Kota Formation of India. |journal=[[Zoological Journal of the Linnean Society]] |date=November 2001 |volume=133 |issue=3 |pages=309–34 |doi=10.1111/j.1096-3642.2001.tb00629.x |doi-access=free}}</ref><ref>{{cite web |title=Sphenodon |url=http://dictionary.reference.com/browse/sphenodon |access-date=8 January 2007 |work=Dictionary.com Unabridged (v 1.1) |publisher=[[Random House]], Inc.}}</ref><ref name="Sophineta">{{cite journal |vauthors=Evans SE, Borsuk-Białynicka M |year=2009|title=A small lepidosauromorph reptile from the Early Triassic of Poland |url=http://palaeontologia.pan.pl/PP65/PP65_179-202.pdf |journal=Paleontologica Polonica |volume=65 |pages=179–202
== Anatomy ==
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Squamates and rhynchocephalians have a number of shared traits ([[Apomorphy and synapomorphy|synapomorphies]]), including fracture planes within the tail vertebrae allowing [[Autotomy#Reptiles and amphibians|caudal autotomy]] (loss of the tail when threatened), transverse [[cloaca]]l slits, an opening in the pelvis known as the thyroid fenestra, the presence of extra [[Ossification center|ossification centres]] in the limb bone [[epiphyses]], a knee joint where a lateral recess on the femur allows the articulation of the fibula, the development of a sexual segment of the kidney, and a number of traits of the feet bones, including a fused [[Talus bone|astralago]]-[[Calcaneus|calcaneun]] and enlarged fourth distal [[Tarsus (skeleton)|tarsal]], which creates a new joint, along with a hooked fifth [[Metatarsal bones|metatarsal]].<ref>{{Cite web |title=Rhynchocephalians |url=https://www.ucl.ac.uk/museums-static/obl4he/vertebratediversity/rhynchocephalians.html |access-date=2022-08-09 |website=[[University College London]]}}</ref>
Like some lizards, the tuatara possesses a [[parietal eye]] (also called a pineal eye or a third eye) covered by scales at the top of the head formed by the parapineal organ, with an accompanying hole in the skull roof enclosed by the [[parietal bones]], dubbed the "pineal foramen", which is also present in fossil rhynchocephalians. The parietal eye detects light (though it is probably not capable of detecting movement or forming images), monitoring the day-night and seasonal cycles, helping to regulate the [[circadian rhythm]], among other functions.<ref>{{cite journal |vauthors=Dendy A |date=1911 |title=VI. On the structure, development and morphological interpretation of the pineal organs and adjacent parts of the brain in the tuatara ( sphenodon punctatus ) |journal=[[Philosophical Transactions of the Royal Society B]] |language=en |volume=201 |issue=274–281 |pages=227–331 |doi=10.1098/rstb.1911.0006 |issn=0264-3960 |doi-access=free}}</ref><ref>{{cite journal |last1=Smith |first1=Krister T. |last2=Bhullar |first2=Bhart-Anjan S. |last3=Köhler |first3=Gunther |last4=Habersetzer |first4=Jörg |date=2 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 |pmid=29614279 |doi-access=free |bibcode=2018CBio...28E1101S |language=en}}</ref><ref name=":17">{{Cite journal |
Rhynchocephalians are distinguished from squamates by a number of traits, including the retention of [[Gastralium|gastralia]] (rib-like bones present in the belly of the body, ancestrally present in [[tetrapod]]s and also present in living [[crocodilia]]ns).<ref name=":2">{{cite book |vauthors=Vitt LJ, Caldwell JP |chapter=Chapter 20: Rhynchocephalians (Sphenodontids) |date=2014 |title=Herpetology |pages=553–554 |publisher=Elsevier |language=en |doi=10.1016/b978-0-12-386919-7.00020-4 |isbn=978-0-12-386919-7 }}</ref> Unlike squamates, but similar to the majority of birds, the tuatara lacks a penis. This is a secondary loss, as a penis or squamate-like [[hemipenes]] were probably present in the last common ancestor of rhynchocephalians and squamates.<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 | [[File:Planocephalosaurus final.svg|thumb|Skull of the basal rhynchocephalian ''[[Planocephalosaurus]],'' which has an open lower temporal fenestra]]
The complete lower temporal bar (caused by the fusion of the [[Jugal bone|jugal]] and [[Quadrate bone|quadtrate]]/[[Quadratojugal bone|quadratojugal]] bones of the skull) of the tuatara, often historically asserted to be a [[Primitive (phylogenetics)|primitive]] feature retained from earlier reptiles, is actually a [[Derived (phylogenetics)|derived]] feature among sphenodontians, with primitive lepidosauromorphs and many rhynchocephalians including the most primitive ones having an open lower [[temporal fenestra]] without a temporal bar.<ref>{{cite book |vauthors=Evans SE, Jones ME |chapter=The Origin, Early History and Diversification of Lepidosauromorph Reptiles |date=2010 |title=New Aspects of Mesozoic Biodiversity |series=Lecture Notes in Earth Sciences |volume=132 |pages=27–44 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |doi=10.1007/978-3-642-10311-7_2 |isbn=978-3-642-10310-0 |bibcode=2010LNES..132...27E}}</ref><ref name=":8">{{cite journal |vauthors=Simões TR, Kinney-Broderick G, Pierce SE |title=An exceptionally preserved Sphenodon-like sphenodontian reveals deep time conservation of the tuatara skeleton and ontogeny |journal=[[Communications Biology]] |volume=5 |issue=1 |
The dentition of most rhynchocephalians, including the tuatara, is described as [[acrodont]], which is associated with the condition of the teeth being attached to the crest of the jaw bone, lacking tooth replacement and having extensive bone growth fusing the teeth to the jaws resulting in the boundary between the teeth and bone being difficult to discern. This differs from the condition found in most lizards (except [[Acrodonta (lizard)|acrodontans]]), which have [[pleurodont]] teeth which are attached to the shelf on the inward-facing side of the jaw, and are replaced throughout life. The teeth of the tuatara have no roots, though the teeth of some other rhynchocephalians possess roots.<ref name=":15" /> The acrodont dentition appears to be a derived character of rhynchocephalians not found in more primitive lepidosauromorphs.<ref name=":18">{{Cite journal |last1=Ford |first1=David P. |last2=Evans |first2=Susan E. |last3=Choiniere |first3=Jonah N. |last4=Fernandez |first4=Vincent |last5=Benson |first5=Roger B. J. |date=2021-08-25 |title=A reassessment of the enigmatic diapsid Paliguana whitei and the early history of Lepidosauromorpha |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=288 |issue=1957 |
Rhynchocephalians possess palatal dentition (teeth present on the bones of the roof of the mouth). Palatal teeth are ancestrally present in tetrapods, but have been lost in many groups. The earliest rhynchocephalians had teeth present on the [[Palatine bone|palatine]], [[Vomer bone|vomer]] and [[Pterygoid bone|pterygoid]] bones, though the vomer and/or the pterygoid teeth are lost in some groups, including the living tuatara, which only has palatine teeth.<ref name=":13" /> A distinctive character found in all rhynchocephalians is the enlargement of the tooth row present on the palatine bones. While in other rhynchocephalians the palatine tooth row is oblique to the teeth of the [[maxilla]], in members of Sphenodontinae (including the tuatara) and Eilenodontinae it is orientated parallel to the maxilla. In these groups, during biting, the teeth of the [[Mandible|dentary]] in the lower jaw slot between the maxillary and palatine tooth rows. This arrangement, which is unique among amniotes, permits [[Three-point flexural test|three point bending]] of food items,<ref name=":7">{{cite journal |vauthors=Jones ME |title=Skull shape and feeding strategy in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria) |journal=Journal of Morphology |volume=269 |issue=8 |pages=945–966 |date=August 2008 |pmid=18512698 |doi=10.1002/jmor.10634 |doi-access=free}}</ref> and in combination with propalinal movement (back and forward motion of the lower jaw) allows for a shearing bite.<ref name=":13">{{cite journal |vauthors=Matsumoto R, Evans SE |title=The palatal dentition of tetrapods and its functional significance |journal=[[Journal of Anatomy]] |volume=230 |issue=1 |pages=47–65 |date=January 2017 |pmid=27542892 |pmc=5192890 |doi=10.1111/joa.12534}}</ref><ref>{{cite journal |vauthors=Jones ME, O'higgins P, Fagan MJ, Evans SE, Curtis N |title=Shearing mechanics and the influence of a flexible symphysis during oral food processing in Sphenodon (Lepidosauria: Rhynchocephalia) |journal=Anatomical Record |volume=295 |issue=7 |pages=1075–1091 |date=July 2012 |pmid=22644955 |doi=10.1002/ar.22487 |doi-access=free}}</ref>[[File:Priosphenodon
The body size of rhynchocephalians is highly variable. The tuatara has an average total length of {{Convert|34.8 and 42.7|cm|in}} for females and males respectively.<ref>{{Cite journal |last1=Herrel |first1=Anthony |last2=Moore |first2=Jennifer A. |last3=Bredeweg |first3=Evan M. |last4=Nelson |first4=Nicola J. |date=2010-05-19 |title=Sexual dimorphism, body size, bite force and male mating success in tuatara: SEXUAL DIMORPHISM IN TUATARA
▲Rhynchocephalians possess palatal dentition (teeth present on the bones of the roof of the mouth). Palatal teeth are ancestrally present in tetrapods, but have been lost in many groups. The earliest rhynchocephalians had teeth present on the [[Palatine bone|palatine]], [[Vomer bone|vomer]] and [[Pterygoid bone|pterygoid]] bones, though the vomer and/or the pterygoid teeth are lost in some groups, including the living tuatara, which only has palatine teeth.<ref name=":13" /> A distinctive character found in all rhynchocephalians is the enlargement of the tooth row present on the palatine bones. While in other rhynchocephalians the palatine tooth row is oblique to the teeth of the [[maxilla]], in members of Sphenodontinae (including the tuatara) and Eilenodontinae it is orientated parallel to the maxilla. In these groups, during biting, the teeth of the [[Mandible|dentary]] in the lower jaw slot between the maxillary and palatine tooth rows. This arrangement, which is unique among amniotes, permits [[Three-point flexural test|three point bending]] of food items,<ref name=":7">{{cite journal |vauthors=Jones ME |title=Skull shape and feeding strategy in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria) |journal=Journal of Morphology |volume=269 |issue=8 |pages=945–966 |date=August 2008 |pmid=18512698 |doi=10.1002/jmor.10634 |doi-access=free}}</ref> and in combination with propalinal movement (back and forward motion of the lower jaw) allows for a shearing bite.<ref name=":13">{{cite journal |vauthors=Matsumoto R, Evans SE |title=The palatal dentition of tetrapods and its functional significance |journal=[[Journal of Anatomy]] |volume=230 |issue=1 |pages=47–65 |date=January 2017 |pmid=27542892 |pmc=5192890 |doi=10.1111/joa.12534}}</ref><ref>{{cite journal |vauthors=Jones ME, O'higgins P, Fagan MJ, Evans SE, Curtis N |title=Shearing mechanics and the influence of a flexible symphysis during oral food processing in Sphenodon (Lepidosauria: Rhynchocephalia) |journal=Anatomical Record |volume=295 |issue=7 |pages=1075–1091 |date=July 2012 |pmid=22644955 |doi=10.1002/ar.22487 |doi-access=free}}</ref>[[File:Priosphenodon avelasi (cropped).jpg|thumb|Skeleton of the herbivorous [[Eilenodontinae|elienodontine]] ''[[Priosphenodon|Priosphenodon avelasi]]'' one of the largest known sphenodontians]]
The tuatara has among the highest known ages of sexual maturity among reptiles,<ref name=":19">{{Cite journal |last1=Hallmann |first1=Konstantin |last2=Griebeler |first2=Eva Maria |date=June 2018 |title=An exploration of differences in the scaling of life history traits with body mass within reptiles and between amniotes |journal=Ecology and Evolution |language=en |volume=8 |issue=11 |pages=5480–5494 |doi=10.1002/ece3.4069 |issn=2045-7758 |pmc=6010814 |pmid=29938067|bibcode=2018EcoEv...8.5480H }}</ref> at around 9 to 13 years of age,<ref>{{Cite journal |last=Newman |first=Donald G. |date=July 1988 |title=Evidence of predation on a young tuatara, ''Sphenodon punctatus'', by kiore, ''Rattus exulans'', on Lady Alice Island |journal=New Zealand Journal of Zoology |volume=15 |issue=3 |pages=443–446 |doi=10.1080/03014223.1988.10422973 |issn=0301-4223}}</ref> and has a high longevity in comparison to lizards of similar size,<ref name=":19" /> with wild individuals likely reaching 70 years, and possibly over 100 years in age.<ref>{{Cite journal |last1=Nelson |first1=Nicola J. |last2=Keall |first2=Susan N. |last3=Pledger |first3=Shirley |last4=Daugherty |first4=Charles H. |date=May 2002 |title=Male-biased sex ratio in a small tuatara population |url=https://onlinelibrary.wiley.com/doi/10.1046/j.1365-2699.2002.00712.x |journal=Journal of Biogeography |language=en |volume=29 |issue=5–6 |pages=633–640 |doi=10.1046/j.1365-2699.2002.00712.x |bibcode=2002JBiog..29..633N |issn=0305-0270}}</ref> Such a late onset of sexual maturity and longevity may have not have been typical of extinct rhynchocephalians.<ref name=":11" /><ref>{{Cite journal |last1=Cavasín |first1=Sol |last2=Cerda |first2=Ignacio |last3=Apesteguia |first3=Sebastian |date=2024 |title=Bone microstructure of Priosphenodon avelasi (Rhynchocephalia: Sphenodontia): paleobiological implications |url=https://www.app.pan.pl/article/item/app010712023.html |journal=Acta Palaeontologica Polonica |volume=69 |doi=10.4202/app.01071.2023|doi-access=free }}</ref>
▲The body size of rhynchocephalians is highly variable. The tuatara has an average total length of {{Convert|34.8 and 42.7|cm|in}} for females and males respectively.<ref>{{Cite journal |last1=Herrel |first1=Anthony |last2=Moore |first2=Jennifer A. |last3=Bredeweg |first3=Evan M. |last4=Nelson |first4=Nicola J. |date=2010-05-19 |title=Sexual dimorphism, body size, bite force and male mating success in tuatara: SEXUAL DIMORPHISM IN TUATARA |url=https://academic.oup.com/biolinnean/article-lookup/doi/10.1111/j.1095-8312.2010.01433.x |journal=Biological Journal of the Linnean Society |language=en |volume=100 |issue=2 |pages=287–292 |doi=10.1111/j.1095-8312.2010.01433.x|doi-access=free }}</ref> ''[[Clevosaurus]] sectumsemper'' has an estimated total length of {{Convert|12|cm|in}},<ref>{{Cite journal |last1=Keeble |first1=Emily |last2=Whiteside |first2=David I. |last3=Benton |first3=Michael J. |date=April 2018 |title=The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures, South Wales, UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia) |url=https://linkinghub.elsevier.com/retrieve/pii/S0016787817301529 |journal=Proceedings of the Geologists' Association |language=en |volume=129 |issue=2 |pages=99–119 |doi=10.1016/j.pgeola.2017.11.001|hdl=1983/5afdc677-3ea0-4519-813d-6052ef8370ec |hdl-access=free }}</ref> while the largest known terrestrial sphenodontian, ''[[Priosphenodon|Priosphenodon avelasi]]'' has an estimated total length of just over {{Convert|100|cm|in}}.<ref name="Apesteguia and Novas 2003">{{cite journal |last1=Apesteguía |first1=Sebastián |last2=Novas |first2=Fernando E. |date=9 October 2003 |title=Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana |journal=Nature |volume=425 |issue=6958 |pages=609–612 |bibcode=2003Natur.425..609A |doi=10.1038/nature01995 |pmid=14534584 |s2cid=4425130}}</ref> The aquatic [[Pleurosauridae|pleurosaurs]] reached lengths of up to {{Convert|150|cm|in}}.<ref name=":11">{{cite journal |vauthors=Klein N, Scheyer TM |date=February 2017 |title=Microanatomy and life history in Palaeopleurosaurus (Rhynchocephalia: Pleurosauridae) from the Early Jurassic of Germany |journal=Die Naturwissenschaften |volume=104 |issue=1–2 |pages=4 |bibcode=2017SciNa.104....4K |doi=10.1007/s00114-016-1427-3 |pmid=28005148 |s2cid=27133670}}</ref>
== Classification ==
[[File:Homeosaurus maximiliani, lizard, Jurassic, Solnhofen Limestone, Eichstatt, Bavaria, Germany - Houston Museum of Natural Science - DSC01988.JPG|thumb|''[[Homoeosaurus|Homeosaurus maximiliani]]'' from the Late Jurassic of Germany]]
While the grouping of Rhynchocephalia is well supported, the relationships of many taxa to each other are uncertain, varying substantially between studies.<ref>{{cite journal |vauthors=Romo de Vivar PR, Martinelli AG, Schmaltz Hsiou A, Soares MB |date=2020-07-02 |title=A New Rhynchocephalian from the Late Triassic of Southern Brazil Enhances Eusphenodontian Diversity |journal=[[Journal of Systematic Palaeontology]] |language=en |volume=18 |issue=13 |pages=1103–1126 |doi=10.1080/14772019.2020.1732488 |bibcode=2020JSPal..18.1103R |issn=1477-2019 |s2cid=216226211}}</ref> In modern cladistics, the clade Sphenodontia includes all rhynchocephalians other than ''[[Wirtembergia]],'' as well as ''[[Gephyrosaurus]]'' and other [[Gephyrosauridae|gephyrosaurids]]. Gephyrosaurids have been found as more closely related to squamates in some analyses.<ref name=":3">{{cite journal |vauthors=Simões TR, Caldwell MW, Pierce SE |date=December 2020 |title=Sphenodontian phylogeny and the impact of model choice in Bayesian morphological clock estimates of divergence times and evolutionary rates |journal=[[BMC Biology]] |volume=18 |issue=1 |
The family [[Sphenodontidae]] has been used to include the tuatara and its closest relatives within Rhynchocephalia. However the grouping has lacked a formal definition, with the included taxa varying substantially between analyses.<ref name=":3" /> The closest relatives of the tuatara are placed in the clade [[Sphenodontinae]], which are characterised by a completely closed temporal bar.<ref name=":8" />
The following is a [[cladogram]] of Rhynchocephalia after DeMar et al. 2022
{{clade|{{clade
Line 129 ⟶ 134:
|1=''[[Ankylosphenodon|Ankylosphenodon pachyostosus]]''
|2=''[[Oenosaurus|Oenosaurus muehlheimensis]]''}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}
Cladogram after Simoes et al.
{{clade|{{clade
Line 188 ⟶ 193:
* †''[[Wirtembergia]]''
* †[[Gephyrosauridae]]?
** †''[[Gephyrosaurus]]''
** †''[[Penegephyrosaurus]]''
* †''[[Bharatagama]]''?
* '''Sphenodontia''' {{small|Williston 1925}}
Line 195 ⟶ 203:
** †''[[Pelecymala]]''
** †''[[Whitakersaurus]]''
** †''[[Parvosaurus]]''
** '''Acrosphenodontia''' {{small|Chambi-Trowell et al., 2021}}
*** †''[[Godavarisaurus]]''
Line 205 ⟶ 213:
**** †''[[Opisthiamimus]]''
**** †''[[Brachyrhinodon]]''
▲**** †''[[Clevosaurus]]''
**** †''[[Colobops]]''?
**** †''[[Lanceirosphenodon]]''
**** †''[[Polysphenodon]]''
**** [[Clevosauridae]]
***** †''[[Clevosaurus]]''
***** †''[[Brachyrhinodon]]''?
***** †''[[Polysphenodon]]''?
**** †''[[Sigmala]]''
**** †''[[Microsphenodon]]''
****
**** '''Neosphenodontia''' {{small|Herrera-Flores et al. 2018}}
***** †''[[Lamarquesaurus]]''
Line 230 ⟶ 241:
****** †[[Sapheosaur]]idae
****** †[[Pleurosauridae]]
{{gallery|Gephyrosaurus skull.
== Ecology ==
[[File:Pleurosaurus goldfussi.JPG|thumb|Skeleton of ''[[Pleurosaurus]],'' an aquatically adapted sphenodontian from the Late Jurassic of Germany]]The fossil record of rhynchocephalians demonstrates that they were a diverse group that exploited a wide array of ecological niches.<ref name=":6" /><ref name=":7" /> Early rhynchocephalians possess small ovoid teeth designed for piercing, and were probably [[insectivore]]s.<ref>{{cite journal |vauthors=Jones ME |title=Dentary Tooth Shape in Sphenodon and Its Fossil Relatives (Diapsida: Lepidosauria: Rhynchocephalia) |veditors=Koppe T, Meyer G, Alt KW, Brook A |journal=[[Frontiers of Oral Biology]] |volume=13 |pages=9–15 |date=2009 |pmid=19828962 |doi=10.1159/000242382 |place=Basel |publisher=Karger |isbn=978-3-8055-9229-1}}</ref> Like modern tuatara, extinct members of Sphenodontinae were likely generalists with a carnivorous/insectivorous diet.<ref>{{Cite journal |last1=Villa |first1=Andrea |last2=Montie |first2=Roel |last3=Röper |first3=Martin |last4=Rothgaenger |first4=Monika |last5=Rauhut |first5=Oliver W. M. |date=2021-05-03 |title=Sphenofontis velserae gen. et sp. nov., a new rhynchocephalian from the Late Jurassic of Brunn (Solnhofen Archipelago, southern Germany) |journal=PeerJ |language=en |volume=9 |pages=e11363 |doi=10.7717/peerj.11363 |issn=2167-8359 |pmc=8101455 |pmid=33987027 |doi-access=free}}</ref> Amongst the most distinct rhynchocephalians are the [[Pleurosauridae|pleurosaurs]], known from the Jurassic of Europe, which were adapted for marine life, with elongated snake-like bodies with reduced limbs, with the specialised Late Jurassic genus ''[[Pleurosaurus]]'' having an elongated triangular skull highly modified from those of other rhynchocephalians. Pleurosaurs are thought to have been [[piscivore]]s (consuming fish).<ref name=":11" /> Several other lineages of rhynchocephalians have been suggested to have had semi-aquatic habits.<ref name=":10">{{cite journal |vauthors=Bever GS, Norell MA |title=A new rhynchocephalian (Reptilia: Lepidosauria) from the Late Jurassic of Solnhofen (Germany) and the origin of the marine Pleurosauridae |journal=Royal Society Open Science |volume=4 |issue=11 |
== Evolutionary history ==
[[File:Clevosaurus.svg|thumb|Skulls of ''[[Clevosaurus|Clevosaurus hudsoni]]'' (left) and ''[[Clevosaurus|Clevosaurus cambrica]]'' (right)]]
The timing of when Rhynchocephalia is estimated to have [[Speciation|diverged]] from Squamata is disputed. Older estimates place the divergence between the [[Guadalupian|Middle Permian]] and earliest Triassic, around 270 to 252 million years ago,<ref name=":3" /> while other authors posit a younger date of around 242 million years ago.<ref name="triassic_origin" /> The oldest known remains of rhynchocephalians are those of ''[[Wirtembergia]]'' known from the [[Erfurt Formation]] near [[Vellberg]] in Southern Germany, dating to the [[Ladinian]] stage of the [[Middle Triassic]], around 238-240 million years old, which is also the most primitive rhynchocephalian known.<ref name=":9" /> Rhynchocephalians underwent considerable diversification during the Late Triassic,<ref name=":6" /> and reached a worldwide distribution across [[Pangaea]] by the end of the Triassic, with the [[Late Triassic]]-[[Early Jurassic]] genus ''[[Clevosaurus]]'' having 10 species across Asia, Africa, Europe, North and South America.<ref>{{cite journal |vauthors=Chambi-Trowell SA, Whiteside DI, Benton MJ, Rayfield EJ |date=November 2020 |veditors=Lautenschlager S |title=Biomechanical properties of the jaws of two species of Clevosaurus and a reanalysis of rhynchocephalian dentary morphospace |journal=[[Palaeontology (journal)|Palaeontology]] |volume=63 |issue=6 |pages=919–939 |doi=10.1111/pala.12493 |bibcode=2020Palgy..63..919C |s2cid=220902843}}</ref> The earliest rhynchocephalians were small animals, but by the Late Triassic the group had evolved a wide range of body sizes.<ref>{{Cite journal |vauthors=Herrera-Flores JA, Elsler A, Stubbs TL, Benton MJ |year=2021|title=Slow and fast evolutionary rates in the history of lepidosaurs |journal=[[Palaeontology (journal)|Palaeontology]] |language=en |volume=65 |issue= |doi=10.1111/pala.12579 |s2cid=244019684 |issn=1475-4983}}</ref> During the Jurassic, rhynchocephalians
== References ==
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