diapsid

File:Skull diapsida 1.svg]]

The name Diapsida means "two arches", and diapsids are traditionally classified based on their two ancestral skull openings (temporal fenestrae) posteriorly above and below the eye. This arrangement allows for the attachment of larger, stronger jaw muscles, and enables the jaw to open more widely. A more obscure ancestral characteristic is a relatively long lower arm bone (the radius) compared to the upper arm bone (humerus).

Basal non-saurian neodiaspids were ancestrally lizard-like, but basal non-saurian neodiapsids include aquatic/amphibious taxa (Claudiosaurus and some tangasaurids){{Cite journal |last1=Nuñez Demarco |first1=Pablo |last2=Meneghel |first2=Melitta |last3=Laurin |first3=Michel |last4=Piñeiro |first4=Graciela |date=2018-07-27 |title=Was Mesosaurus a Fully Aquatic Reptile? |journal=Frontiers in Ecology and Evolution |volume=6 |pages=109 |doi=10.3389/fevo.2018.00109 |issn=2296-701X |doi-access=free |hdl-access=free |hdl=20.500.12008/30631}} the gliding lizard-like Weigeltisauridae,{{Cite journal |last1=Pritchard |first1=Adam C. |last2=Sues |first2=Hans-Dieter |last3=Scott |first3=Diane |last4=Reisz |first4=Robert R. |date=2021-05-20 |title=Osteology, relationships and functional morphology of Weigeltisaurus jaekeli (Diapsida, Weigeltisauridae) based on a complete skeleton from the Upper Permian Kupferschiefer of Germany |journal=PeerJ |language=en |volume=9 |pages=e11413 |doi=10.7717/peerj.11413 |issn=2167-8359 |pmc=8141288 |pmid=34055483 |doi-access=free}} as well as the Triassic chameleon-like drepanosaurs.{{Cite journal |last1=Pritchard |first1=Adam C. |last2=Nesbitt |first2=Sterling J. |date=October 2017 |title=A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida |journal=Royal Society Open Science |language=en |volume=4 |issue=10 |pages=170499 |bibcode=2017RSOS....470499P |doi=10.1098/rsos.170499 |issn=2054-5703 |pmc=5666248 |pmid=29134065}}

Diapsids were originally classified as one of four subclasses of the class Reptilia, all of which were based on the number and arrangement of openings in the skull. The other three subclasses were Synapsida (one opening low on the skull, for the "mammal-like reptiles"), Anapsida (no skull opening, including turtles and their relatives), and Euryapsida (one opening high on the skull, including many prehistoric marine reptiles). With the advent of phylogenetic nomenclature, this system of classification was heavily modified. Today, the synapsids are often not considered true reptiles, while Euryapsida were found to be an unnatural assemblage of diapsids that had lost one of their skull openings. Genetic studies and the discovery of the Triassic Pappochelys have shown that this is also the case in turtles, which are actually heavily modified diapsids. In phylogenetic systems, birds (descendants of traditional diapsid reptiles) are also considered to be members of this group.

Some modern studies of reptile relationships have preferred to use the name "diapsid" to refer to the crown group of all modern diapsid reptiles but not their extinct relatives. However, many researchers have also favored a more traditional definition that includes the prehistoric araeoscelidians. In 1991, Laurin defined Diapsida as a clade, "the most recent common ancestor of araeoscelidians, lepidosaurs, and archosaurs, and all its descendants".Benton, M. J., Donoghue, P. C., Asher, R. J., Friedman, M., Near, T. J., & Vinther, J. (2015). "Constraints on the timescale of animal evolutionary history." Palaeontologia Electronica, 18.1.1FC; 1-106; palaeo-electronica.org/content/fc-1

The clade Neodiapsida was given a phylogenetic definition by Laurin in 1991. He defined it as the branch-based clade containing all animals more closely related to "Younginiformes" (later, more specifically, emended to Youngina capensis) than to Petrolacosaurus (representing Araeoscelidia).{{cite journal |last1=Reisz |first1=Robert R. |last2=Modesto |first2=Sean P. |last3=Scott |first3=Diane M. |date=22 December 2011 |title=A new Early Permian reptile and its significance in early diapsid evolution |journal=Proceedings of the Royal Society B: Biological Sciences |volume=278 |issue=1725 |pages=3731–3737 |doi=10.1098/rspb.2011.0439 |pmc=3203498 |pmid=21525061}} The earliest known neodiapsids like Orovenator are known from the Early Permian, around 290 million years ago.{{Cite journal |last1=Reisz |first1=Robert R. |last2=Modesto |first2=Sean P. |last3=Scott |first3=Diane M. |date=2011-12-22 |title=A new Early Permian reptile and its significance in early diapsid evolution |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=278 |issue=1725 |pages=3731–3737 |doi=10.1098/rspb.2011.0439 |issn=0962-8452 |pmc=3203498 |pmid=21525061}}

All genetic studies have supported the hypothesis that turtles are cladistically diapsid reptiles despite being morphologically anapsid, most placing them as more closely related to living archosaurs (including crocodiles and birds) than to lepidosaurs (lizards, snakes, etc).{{cite journal |last1=Zardoya |first1=R. |last2=Meyer |first2=A. |year=1998 |title=Complete mitochondrial genome suggests diapsid affinities of turtles |journal=Proc Natl Acad Sci U S A |volume=95 |issue=24 |pages=14226–14231 |bibcode=1998PNAS...9514226Z |doi=10.1073/pnas.95.24.14226 |issn=0027-8424 |pmc=24355 |pmid=9826682 |doi-access=free}}{{Cite journal |last=Iwabe |first=N. |author2=Hara, Y. |author3=Kumazawa, Y. |author4=Shibamoto, K. |author5=Saito, Y. |author6=Miyata, T. |author7=Katoh, K. |date=2004-12-29 |title=Sister group relationship of turtles to the bird-crocodilian clade revealed by nuclear DNA-coded proteins |journal=Molecular Biology and Evolution |volume=22 |issue=4 |pages=810–813 |doi=10.1093/molbev/msi075 |pmid=15625185 |doi-access=free}}{{Cite journal |last=Roos |first=Jonas |author2=Aggarwal, Ramesh K. |author3=Janke, Axel |date=Nov 2007 |title=Extended mitogenomic phylogenetic analyses yield new insight into crocodylian evolution and their survival of the Cretaceous–Tertiary boundary |journal=Molecular Phylogenetics and Evolution |volume=45 |issue=2 |pages=663–673 |doi=10.1016/j.ympev.2007.06.018 |pmid=17719245|bibcode=2007MolPE..45..663R }}{{Cite journal |last=Katsu |first=Y. |author2=Braun, E. L. |author3=Guillette, L. J. Jr. |author4=Iguchi, T. |date=2010-03-17 |title=From reptilian phylogenomics to reptilian genomes: analyses of c-Jun and DJ-1 proto-oncogenes |journal=Cytogenetic and Genome Research |volume=127 |issue=2–4 |pages=79–93 |doi=10.1159/000297715 |pmid=20234127 |s2cid=12116018}}

Modern reptiles and birds are placed within the neodiapsid subclade Sauria, defined as the last common ancestor of Lepidosauria (which includes lizards, snakes and the tuatara), and Archosauria (which includes crocodilians and dinosaurs, including birds, among others).{{Cite journal |last1=Simões |first1=Tiago R. |last2=Kammerer |first2=Christian F. |last3=Caldwell |first3=Michael W. |last4=Pierce |first4=Stephanie E. |name-list-style=and |year=2022 |title=Successive climate crises in the deep past drove the early evolution and radiation of reptiles |journal=Science Advances |volume=8 |issue=33 |pages=eabq1898 |bibcode=2022SciA....8.1898S |doi=10.1126/sciadv.abq1898 |pmc=9390993 |pmid=35984885 |doi-access=free}}

A cladistic analysis by Laurin and Piñeiro (2017) recovers Parareptilia as part of Diapsida, with pareiasaurs, turtles, millerettids, and procolophonoids recovered as more derived than the basal diapsid Younginia.{{Cite journal |last1=Laurin |first1=Michel |last2=Piñeiro |first2=Graciela H. |year=2017 |title=A Reassessment of the Taxonomic Position of Mesosaurs, and a Surprising Phylogeny of Early Amniotes |url=https://hal.archives-ouvertes.fr/hal-01618314/file/Laurin%20%26%20Pin%CC%83eiro%20ms%20R1%20cl.pdf |journal=Frontiers in Earth Science |volume=5 |page=88 |bibcode=2017FrEaS...5...88L |doi=10.3389/feart.2017.00088 |s2cid=32426159 |doi-access=free}} A 2020 study by David P. Ford and Roger B. J. Benson also recovered Parareptilia as deeply nested within Diapsida as the sister group to Neodiapsida. They united this relationship between Parareptilia and Neodiapsida in the new clade Neoreptilia, defining it as the last common ancestor and all descendants of Procolophon trigoniceps and Youngina capensis.{{cite journal |vauthors=Ford DP, Benson RB |date=January 2020 |title=The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae |url=https://ora.ox.ac.uk/objects/uuid:cb6f5486-7889-47fe-beff-515795468442 |journal=Nature Ecology & Evolution |volume=4 |issue=1 |pages=57–65 |doi=10.1038/s41559-019-1047-3 |pmid=31900445 |s2cid=209673326}} However, this excludes mesosaurs, who were found to be basal among the sauropsids.{{cite journal |vauthors=Ford DP, Benson RB |date=January 2020 |title=The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae |url=https://ora.ox.ac.uk/objects/uuid:cb6f5486-7889-47fe-beff-515795468442 |journal=Nature Ecology & Evolution |volume=4 |issue=1 |pages=57–65 |doi=10.1038/s41559-019-1047-3 |pmid=31900445 |s2cid=209673326}} Other recent studies have found the more traditional arrangement of parareptiles being outside of Diapsida.

The position of the highly derived Mesozoic marine reptile groups Thalattosauria, Ichthyosauromorpha and Sauropterygia within Neodiapsida is uncertain, and they may lie within Sauria.{{Cite journal |last1=Wolniewicz |first1=Andrzej S |last2=Shen |first2=Yuefeng |last3=Li |first3=Qiang |last4=Sun |first4=Yuanyuan |last5=Qiao |first5=Yu |last6=Chen |first6=Yajie |last7=Hu |first7=Yi-Wei |last8=Liu |first8=Jun |date=2023-08-08 |editor-last=Ibrahim |editor-first=Nizar |title=An armoured marine reptile from the Early Triassic of South China and its phylogenetic and evolutionary implications |journal=eLife |volume=12 |pages=e83163 |doi=10.7554/eLife.83163 |pmid=37551884 |pmc=10499374 |issn=2050-084X|doi-access=free }}

In the 2022 and 2023 studies, Araeoscelidia was found to have no close relationship with Neodiapsida and was not even part of Sauropsida.{{cite journal |last1=Klembara |first1=J. |last2=Ruta |first2=M. |last3=Anderson |first3=J. |last4=Mayer |first4=T. |last5=Hain |first5=M. |last6=Valaška |first6=D. |date=2023 |title=A review of Coelostegus prothales Carroll and Baird, 1972 from the Upper Carboniferous of the Czech Republic and the interrelationships of basal eureptiles |journal=PLOS ONE |volume=18 |issue=9 |pages=e0291687 |bibcode=2023PLoSO..1891687K |doi=10.1371/journal.pone.0291687 |pmc=10513281 |pmid=37733816 |doi-access=free}}

Below are cladograms showing the relations of the major groups of diapsids.

Cladogram after Bickelmann et al., 2009{{cite journal |last1=Bickelmann |first1=Constanze |last2=Müller |first2=Johannes |last3=Reisz |first3=Robert R. |name-list-style=and |year=2009 |title=The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of younginiform reptiles |journal=Canadian Journal of Earth Sciences |volume=49 |issue=9 |pages=651–661 |bibcode=2009CaJES..46..651S |doi=10.1139/E09-038}} and Reisz et al., 2011:{{cite journal |last1=Reisz |first1=Robert R. |last2=Modesto |first2=Sean P. |last3=Scott |first3=Diane M. |name-list-style=and |year=2011 |title=A new Early Permian reptile and its significance in early diapsid evolution |journal=Proceedings of the Royal Society B |volume=278 |issue=1725 |pages=3731–7 |doi=10.1098/rspb.2011.0439 |pmc=3203498 |pmid=21525061}}

{{clade

|1={{clade

|label1=Sauropsida

|1={{clade

|label1={{extinct}}Parareptilia

|1={{clade

|1={{clade

|label1=

|1={{extinct}}Millerettidae 50px

}}

|label2=

|2={{clade

|1={{clade

|label1=

|1= {{extinct}}Eunotosaurus

}}

|label2={{extinct}}Hallucicrania

|2={{clade

|1={{extinct}}Lanthanosuchidae 50px

|label2={{extinct}}Procolophonia

|2={{clade

|label1=

|1={{extinct}}Procolophonoidea 50px

|2={{extinct}}Pareiasauromorpha 60px

}}

}}

}}

}}

|label2=Eureptilia

|2={{clade

|1={{clade

|label1=

|1= {{extinct}}Captorhinidae 50px

}}

|label2=Romeriida

|2={{clade

|1={{clade

|label1=

|1={{extinct}}Paleothyris

}}

|label2=Diapsida

|2={{clade

|1={{extinct}}Araeoscelidia

|label2=Neodiapsida

|2={{clade

|label1=

|1={{extinct}}Orovenator

|2={{clade

|label1=

|1={{extinct}}Lanthanolania

|2={{clade

|label1=

|1={{extinct}}Tangasauridae

|2={{clade

|label1=

|1={{extinct}}Younginidae

|2={{clade

|label1=

|1={{clade

|label1=

|1={{extinct}}Claudiosaurus

}}

|2={{clade

|label1=

|1={{clade

|label1=

|1={{clade

|label1=

|1={{extinct}}Palaeagama

|2={{extinct}}Saurosternon

}}

}}

|2={{clade

|label1=

|1={{clade

|label1=

|1={{extinct}}Coelurosauravus

}}

|2={{clade

|1={{clade

|label1=

|1={{extinct}}Thalattosauria

|2={{clade

|label1=

|1={{extinct}}Hupehsuchia

|2={{extinct}}Ichthyopterygia

}}

}}

|label2=Sauria

|2={{clade

|label1=

|1=Lepidosauromorpha

|2=Archosauromorpha

}}

}}

}}

}}

}}

}}

}} }} }} }} }} }} }}

}}

}}

The cladogram of Lee (2013) below used a combination of genetic (molecular) and fossil (morphological) data.{{Cite journal |last1=Lee |first1=M. S. Y. |year=2013 |title=Turtle origins: Insights from phylogenetic retrofitting and molecular scaffolds |journal=Journal of Evolutionary Biology |volume=26 |issue=12 |pages=2729–2738 |doi=10.1111/jeb.12268 |pmid=24256520 |s2cid=2106400 |doi-access=free}}

{{clade|{{clade

|1={{extinct}}Araeoscelidia 50px

|label2=Neodiapsida

|2={{clade

|1={{extinct}}Claudiosaurus80px

|2={{clade

|1={{extinct}}Younginiformes80px

|label2=Sauria

|2={{clade

|label1=Lepidosauromorpha

|1={{clade

|1={{extinct}}Kuehneosauridae80px

|label2=Lepidosauria

|2={{clade

|1=Rhynchocephalia (tuatara and their extinct relatives)80px

|2=Squamata (lizards and snakes)80px}} }}

|label2=Archosauromorpha

|2={{clade

|1={{clade

|1={{extinct}}Choristodera80px

|2={{clade

|1={{extinct}}Prolacertiformes80px

|2={{clade

|1={{clade

|1={{extinct}}Rhynchosauria80px

|2={{extinct}}Trilophosaurus80px

}}

|2=Archosauriformes (crocodiles, birds, and their extinct relatives) 80px

}} }} }}

}}

}}

}}

}}

}}|label1=Diapsida}}

This second cladogram is based on the 2017 study by Pritchard and Nesbitt.{{Cite journal |last1=Pritchard |first1=Adam C. |last2=Nesbitt |first2=Sterling J. |date=2017-10-11 |title=A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida |journal=Royal Society Open Science |volume=4 |issue=10 |page=170499 |bibcode=2017RSOS....470499P |doi=10.1098/rsos.170499 |issn=2054-5703 |pmc=5666248 |pmid=29134065}}

{{clade|{{clade

|1={{extinct}}Orovenator80px

|2={{clade

|1={{extinct}}Drepanosauromorpha80px

|2={{clade

|1={{extinct}}Weigeltisauridae80px

|2={{clade

|1={{extinct}}Claudiosaurus80px

|2={{clade

|1={{extinct}}Tangasauridae80px (Hovasaurus, Thadeosaurus, Acerosodontosaurus)

|2={{extinct}}Younginidae (Youngina+unnamed species)

|label3=Sauria

|3={{clade

|1=Lepidosauria80px

|label2=Archosauromorpha

|2={{clade

|1={{extinct}}Protorosaurus80px

|2={{clade

|1={{extinct}}Tanystropheidae80px

|2={{clade

|1={{extinct}}Rhynchosauria80px

|2={{clade

|1={{extinct}}Allokotosauria80px

|2={{clade

|1={{extinct}}Prolacerta80px

|2=Archosauriformes80px

}} }} }} }} }} }} }} }} }} }} }}|label1=Neodiapsida}}

The following cladogram was found by Simões et al. (2022):

{{clade

|label1={{vert-label|Neoreptilia}}

|{{clade

|1={{extinct}}Procolophonomorpha80px

|label2={{vert-label|Neodiapsida}}

|2={{clade

|1={{extinct}}Younginiformes80px

|2={{clade

|1={{extinct}}Eunotosaurus

|2={{clade

|1={{extinct}}Weigeltisauridae80px

|label2={{vert-label|Sauria}}

|2={{clade

|label1=Lepidosauromorpha

|1={{clade

|1=Rhynchocephalia (tuatara and their extinct relatives)80px

|2=Squamata (lizards and snakes)80px}}

|label2=Archelosauria

|2={{clade

|1=Pantestudines (turtles and extinct relatives)50px

|label2={{vert-label|Archosauromorpha}}

|2={{clade

|1={{clade

|1={{extinct}}Ichthyosauromorpha80px

|2={{clade

|1={{extinct}}Sauropterygia 80px

|2={{extinct}}Thalattosauria 80px

}}

}}

|2={{clade

|label1={{extinct}}Protorosauria

|1={{clade

|1={{extinct}}Protorosauridae80px

|2={{clade

|1={{extinct}}Tanystropheidae80px

|2={{clade

|1={{extinct}}Drepanosauromorpha80px

|2={{extinct}}Kuehneosauridae80px

}}

}}

}}

|2={{clade

|1={{clade

|1={{extinct}}Allokotosauria80px

|2={{extinct}}Rhynchosauria80px

}}

|2=Archosauriformes (crocodiles, birds, and their extinct relatives) 80px

}}

}}

}}

}}

}}

}}

}}

}}

}}

}}

• Vertebrate paleontology
• Synapsida
• Anapsid
• Euryapsida

{{Reflist}}

{{Commonscat|Diapsida}}

• {{Wikispecies-inline}}
• [http://tolweb.org/tree?group=Diapsida&contgroup=Amniota Diapsida]. Michel Laurin and Jacques A. Gauthier. Tree of Life Web Project. June 22, 2000.

{{Chordata}}

{{Eureptilia|E.|state=autocollapse}}

{{Reptiles}}

{{Taxonbar|from=Q134688}}

01

Category:Reptile taxonomy

Category:Reptiles of the United States

Category:Extant Pennsylvanian first appearances

Category:Taxa named by Henry Fairfield Osborn