View source for Diapsid

{{short description|Clade of reptiles with two holes in each side of their skulls}}
{{Automatic taxobox
| name = Diapsida
| fossil_range = {{fossilrange|Permian|Present|earliest=Pennsylvanian}} possible [[Late Carboniferous]] records
| image = Youngina skull lateral.png
| image_caption = Reconstructed skull of ''[[Youngina]]'' (a basal member of Neodiapsida)
| image2 = Nile crocodile head.jpg
| image2_caption = [[Nile crocodile]] (''Crocodylus niloticus'')
| taxon = Diapsida
| authority = [[Henry Fairfield Osborn|Osborn]], 1903
| subdivision_ranks = Subgroups
| subdivision = 
* {{extinct}}''[[Dolerosaurus]]''
* {{extinct}}[[Araeoscelidia]]?
* {{extinct}}[[Millerettidae]]？
* {{extinct}}[[Parareptilia]]?
*'''Neodiapsida'''
**{{extinct}}''[[Acallosuchus]]''
**{{extinct}}''[[Akkedops]]''
**{{extinct}}''[[Claudiosaurus]]''
**{{extinct}}''[[Elachistosuchus]]'' 
**{{extinct}}''[[Eunotosaurus]]''?
**{{extinct}}''[[Kenyasaurus]]''
**{{extinct}}''[[Kudnu]]''
**{{extinct}}''[[Lanthanolania]]''?
**{{extinct}}''[[Maiothisavros]]''
**{{extinct}}''[[Orovenator]]''?
**{{extinct}}''[[Palacrodon]]''
**{{extinct}}''[[Palaeagama]]''
**{{extinct}}''[[Saurosternon]]''
**{{extinct}}[[Younginiformes]] (possibly paraphyletic)
***{{extinct}}[[Tangasauridae]]
***{{extinct}}[[Younginidae]]
**{{extinct}}[[Avicephala]] (possibly non-monophyletic)
***{{extinct}}[[Drepanosauromorpha]]
***{{extinct}}[[Weigeltisauridae]]
**{{extinct}}'''[[Choristodera]]'''
**{{extinct}}'''[[Ichthyosauromorpha]]'''
**{{extinct}}'''[[Sauropterygia]]'''
**{{extinct}}'''[[Thalattosauria]]'''
**'''[[Sauria]] (modern reptiles and birds)'''
}}{{Split|date=August 2025|Neodiapsida}}
'''Diapsids''' ("two arches") are a clade of [[sauropsids]], distinguished from more primitive [[eureptiles]] by the presence of two holes, known as [[temporal fenestra]]e, in each side of their [[skull]]s. The earliest traditionally identified diapsids, the [[Araeoscelidia|araeoscelidians]], appeared about three hundred [[million years ago]] during the late [[Carboniferous]] period.<ref>{{Cite web|url=https://ucmp.berkeley.edu/taxa/verts/diapsida.php|title=Diapsida|website=ucmp.berkeley.edu}}</ref> All diapsids other than the most primitive ones in the clade Araeoscelidia are often placed into the clade '''Neodiapsida'''. The diapsids are extremely diverse, and include birds and all modern reptile groups, including [[turtle]]s, which were historically thought to lie outside the group.<ref>{{Cite journal |last1=Schoch |first1=Rainer R. |last2=Sues |first2=Hans-Dieter |author-link2=Hans-Dieter Sues |year=2016 |title=The diapsid origin of turtles |journal=Zoology |volume=119 |issue=3 |pages=159–161 |doi=10.1016/j.zool.2016.01.004 |pmid=26934902|bibcode=2016Zool..119..159S }}</ref> All modern reptiles and birds are placed within the neodiapsid subclade [[Sauria]]. Although some diapsids have lost either one hole (lizards), or both holes (snakes and turtles), or have a heavily restructured skull (modern birds), they are still [[scientific classification|classified]] as diapsids based on their ancestry. At least 17,084 [[species]] of diapsid animals are extant: 9,159 birds,<ref name="Barrow">{{cite journal |last1=Barrowclough |first1=George F. |last2=Cracraft |first2=Joel |last3=Klicka |first3=John |last4=Zink |first4=Robert M. |name-list-style=and |date=23 November 2016 |editor-last=Green |editor-first=Andy J |title=How Many Kinds of Birds Are There and Why Does It Matter? |journal=PLOS ONE |volume=11 |issue=11 |article-number=e0166307 |bibcode=2016PLoSO..1166307B |doi=10.1371/journal.pone.0166307 |pmc=5120813 |pmid=27880775 |doi-access=free}}</ref> and 7,925 snakes, lizards, [[tuatara]], turtles, and crocodiles.<ref>{{Cite journal |last1=Reeder |first1=Tod W. |last2=Townsend |first2=Ted M. |last3=Mulcahy |first3=Daniel G. |last4=Noonan |first4=Brice P. |last5=Wood |first5=Perry L. Jr. |last6=Sites |first6=Jack W. Jr. |last7=Wiens |first7=John J. |name-list-style=and |year=2015 |editor-last=Wilf |editor-first=Peter |title=Integrated Analyses Resolve Conflicts over Squamate Reptile Phylogeny and Reveal Unexpected Placements for Fossil Taxa |journal=PLOS ONE |volume=10 |issue=3 |article-number=e0118199 |bibcode=2015PLoSO..1018199R |doi=10.1371/journal.pone.0118199 |pmc=4372529 |pmid=25803280 |doi-access=free}}</ref>

==Characteristics==
[[File:Skull diapsida 1.svg|thumb|left|Diagram of the diapsid skull with temporal openings, unlike in [[Anapsida|anapsids]]]]

The name Diapsida means "two arches", and diapsids are traditionally classified based on their two ancestral skull openings ([[temporal fenestra]]e) 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 (bone)|radius]]) compared to the upper arm bone ([[humerus]]).

Basal non-saurian neodiapsids were ancestrally lizard-like, but basal non-saurian neodiapsids include aquatic/amphibious taxa (''[[Claudiosaurus]]'' and some [[Tangasauridae|tangasaurids]])<ref>{{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 |article-number=109 |doi=10.3389/fevo.2018.00109 |bibcode=2018FrEEv...6..109N |issn=2296-701X |doi-access=free |hdl-access=free |hdl=20.500.12008/30631}}</ref> the [[gliding lizard]]-like [[Weigeltisauridae]],<ref name=":0">{{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 |article-number=e11413 |doi=10.7717/peerj.11413 |issn=2167-8359 |pmc=8141288 |pmid=34055483 |doi-access=free}}</ref> as well as the Triassic chameleon-like [[Drepanosaur|drepanosaurs]].<ref>{{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 |article-number=170499 |bibcode=2017RSOS....470499P |doi=10.1098/rsos.170499 |issn=2054-5703 |pmc=5666248 |pmid=29134065}}</ref>

==Classification==
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"), [[Anapsid]]a (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 [[araeoscelidia]]ns. In 1991, Laurin defined Diapsida as a [[clade]], "the most recent common ancestor of araeoscelidians, [[lepidosaurs]], and [[archosaur]]s, and all its descendants".<ref name=bentonetal2015>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</ref>

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]]).<ref>{{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}}</ref> The earliest known neodiapsids like ''[[Orovenator]]'' are known from the Early [[Permian]], around 290 million years ago.<ref>{{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}}</ref>

All [[Molecular phylogenetics|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).<ref name="Zardoya2">{{cite journal |last1=Zardoya |first1=R. |last2=Meyer |first2=A. |year=1998 |title=Complete mitochondrial genome suggests diapsid affinities of turtles |journal=[[Proceedings of the National Academy of Sciences|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}}</ref><ref name="Iwabe2">{{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}}</ref><ref name="Roos2">{{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 }}</ref><ref name="Katsu2">{{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}}</ref>

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).<ref name="Simões2022">{{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 |article-number=eabq1898 |bibcode=2022SciA....8.1898S |doi=10.1126/sciadv.abq1898 |pmc=9390993 |pmid=35984885 |doi-access=free}}</ref>

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]]''.<ref>{{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 |article-number=88 |bibcode=2017FrEaS...5...88L |doi=10.3389/feart.2017.00088 |hdl=20.500.12008/33548 |s2cid=32426159 |doi-access=free}}</ref> 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]]''.<ref name=":5">{{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}}</ref> However, this excludes [[mesosaur]]s, who were found to be basal among the sauropsids.<ref name=":5">{{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}}</ref> Other recent studies have found the more traditional arrangement of parareptiles being outside of Diapsida.<ref name="Simões2022" />

The position of the highly derived Mesozoic marine reptile groups [[Thalattosauria]], [[Ichthyosauromorpha]] and [[Sauropterygia]] within Neodiapsida is uncertain, and they may lie within Sauria.<ref name="Simões2022" /><ref>{{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 |article-number=e83163 |doi=10.7554/eLife.83163 |pmid=37551884 |pmc=10499374 |issn=2050-084X|doi-access=free }}</ref>

In the 2022 and 2023 studies, Araeoscelidia was found to have no close relationship with Neodiapsida and was not even part of Sauropsida.<ref name="Simões2022" /><ref name="Klembara2023">{{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 |article-number=e0291687 |bibcode=2023PLoSO..1891687K |doi=10.1371/journal.pone.0291687 |pmc=10513281 |pmid=37733816 |doi-access=free}}</ref>
===Relationships===
Below are [[cladogram|cladograms]] showing the relations of the major groups of diapsids.

Cladogram after Bickelmann ''et al.'', 2009<ref name="Bickelmann09">{{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}}</ref> and Reisz ''et al.'', 2011:<ref name="Orovenator">{{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}}</ref>

{{clade
|1={{clade
      |label1=[[Sauropsida]] 
      |1={{clade
         |label1={{extinct}}[[Parareptilia]] 
         |1={{clade
               |1={{clade
                  |label1=      
                  |1={{extinct}}[[Millerettid]]ae [[Image:Milleretta BW.jpg|50px]]
                  }}
               |label2=  
               |2={{clade
                  |1={{clade
                     |label1=    
                     |1= {{extinct}}''[[Eunotosaurus]]''
                     }}
                  |label2={{extinct}}[[Hallucicrania]] 
                  |2={{clade
                    |1={{extinct}}[[Lanthanosuchidae]] [[Image:Lanthanosuchus watsoni.jpg|50px]]
                    |label2={{extinct}}[[Procolophonia]] 
                    |2={{clade
                        |label1=  
                        |1={{extinct}}[[Procolophonoidea]] [[Image:Sclerosaurus1DB.jpg|50px]]
                        |2={{extinct}}[[Pareiasauromorpha]] [[Image:Scutosaurus BW.jpg|60px]]
                        }}
                     }}
                 }}
             }}
      |label2=[[Eureptilia]]
      |2={{clade
         |1={{clade
            |label1=    
            |1= {{extinct}}[[Captorhinidae]] [[Image:Labidosaurus.jpg|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]]  [[File:Youngina capensis.png|80px]]
                           |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.<ref name="scaffold2013">{{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}}</ref>

{{clade|{{clade
               |1={{extinct}}[[Araeoscelidia]] [[Image:Spinoaequalis schultzei reconstruction.jpg|50px]]
               |label2=Neodiapsida
               |2={{clade
               |1={{extinct}}''[[Claudiosaurus]]''[[File:Claudiosaurus white background.jpg|80px]]
               |2={{clade
                  |1={{extinct}}[[Younginiformes]][[File:Hovasaurus BW flipped.jpg|80px]]
                  |label2=[[Sauria]]
                  |2={{clade
                     |label1=[[Lepidosauromorpha]]
                     |1={{clade
                         |1={{extinct}}[[Kuehneosauridae]][[File:Icarosaurus white background.jpg|80px]]
                         |label2=[[Lepidosauria]]
                         |2={{clade
                            |1=[[Rhynchocephalia]] ([[tuatara]] and their extinct relatives)[[File:Hatteria white background.jpg|80px]]
                            |2=[[Squamata]] ([[lizard]]s and [[snake]]s)[[File:British reptiles, amphibians, and fresh-water fishes (1920) (Lacerta agilis).jpg|80px]]}} }}
                     |label2=[[Archosauromorpha]]
                     |2={{clade
                        |1={{clade
                           |1={{extinct}}[[Choristodera]][[File:Hyphalosaurus_mmartyniuk_wiki.png|80px]]
                           |2={{clade
                              |1={{extinct}}[[Prolacertiformes]][[File:Prolacerta broomi.jpg|80px]]
                              |2={{clade
                                   |1={{clade
                                      |1={{extinct}}[[Rhynchosaur]]ia[[File:Hyperodapedon BW2 white background.jpg|80px]]
                                      |2={{extinct}}''[[Trilophosaurus]]''[[File:Trilophosaurus buettneri (flipped).jpg|80px]]
                                      }}
                                   |2=[[Archosauriformes]]  ([[Crocodilia|crocodiles]], [[bird]]s, and their extinct relatives) <span style="{{MirrorH}}">[[File:Deinosuchus riograndensis.png|80px]]</span>

}} }} }}

                        }}
                     }}
                  }}
               }}
            }}|label1=Diapsida}}

This second cladogram is based on the 2017 study by Pritchard and Nesbitt.<ref>{{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 |article-number=170499 |bibcode=2017RSOS....470499P |doi=10.1098/rsos.170499 |issn=2054-5703 |pmc=5666248 |pmid=29134065}}</ref>

{{clade|{{clade
      |1={{extinct}}''[[Orovenator]]''[[File:Orovenator.jpg|80px]]
      |2={{clade
         |1={{extinct}}[[Drepanosauromorpha]][[File:Megalancosaurus BW.jpg|80px]]
         |2={{clade
            |1={{extinct}}[[Weigeltisauridae]][[File:Weigeltisaurus_reconstruction.png|80px]]
            |2={{clade
               |1={{extinct}}''[[Claudiosaurus]]''[[File:Claudiosaurus white background.jpg|80px]]
               |2={{clade
                  |1={{extinct}}[[Tangasauridae]][[File:Hovasaurus BW flipped.jpg|80px]] (''[[Hovasaurus]]'', ''[[Thadeosaurus]]'', ''[[Acerosodontosaurus]]'')
                  |2={{extinct}}[[Younginidae]] (''[[Youngina]]''+unnamed species)  [[File:Youngina capensis.png|80px]]
                  |label3=[[Sauria]]
                  |3={{clade
                     |1=[[Lepidosauria]][[File:Zoology of Egypt (1898) (Varanus griseus).png|80px]]
                     |label2=[[Archosauromorpha]]
                     |2={{clade
                        |1={{extinct}}''[[Protorosaurus]]''[[File:Protorosaurus BW.jpg|80px]]
                        |2={{clade
                           |1={{extinct}}[[Tanystropheidae]][[File:Macrocnemus BW.jpg|80px]]
                           |2={{clade
                              |1={{extinct}}[[Rhynchosauria]][[File:Hyperodapedon BW2 white background.jpg|80px]]
                              |2={{clade
                                 |1={{extinct}}[[Allokotosauria]][[File:Trilophosaurus buettneri (flipped).jpg|80px]]
                                 |2={{clade
                                    |1={{extinct}}''[[Prolacerta]]''[[File:Prolacerta broomi.jpg|80px]]
                                    |2=[[Archosauriformes]]<span style="{{MirrorH}}">[[File:Deinosuchus riograndensis.png|80px]]</span>
}} }} }} }} }} }} }} }} }} }} }}|label1=Neodiapsida}}

The following cladogram was found by Simões ''et al''. (2022): <ref name="Simões2022" />

{{clade
|label1={{vert-label|Neoreptilia}}
|{{clade
  |1={{extinct}}[[Procolophonomorpha]][[File:Scutosaurus BW.jpg|80px]]
  |label2={{vert-label|'''Neodiapsida'''}}
  |2={{clade
    |1={{extinct}}[[Younginiformes]][[File:Hovasaurus BW flipped.jpg|80px]]
    |2={{clade
      |1={{extinct}}''[[Eunotosaurus]]''
      |2={{clade
        |1={{extinct}}[[Weigeltisauridae]][[File:Weigeltisaurus_reconstruction.png|80px]]
        |label2={{vert-label|[[Sauria]]}}
        |2={{clade
          |label1=[[Lepidosauromorpha]]
          |1={{clade
            |1=[[Rhynchocephalia]] ([[tuatara]] and their extinct relatives)[[File:Hatteria white background.jpg|80px]]
            |2=[[Squamata]] ([[lizard]]s and [[snake]]s)[[File:British reptiles, amphibians, and fresh-water fishes (1920) (Lacerta agilis).jpg|80px]]}} 
            |label2=[[Archelosauria]]
              |2={{clade
              |1=[[Pantestudines]] ([[turtle]]s and extinct relatives)[[File:Erpétologie générale, ou, Histoire naturelle complète des reptiles (Centrochelys sulcata).jpg|50px]]
              |label2={{vert-label|[[Archosauromorpha]]}}
              |2={{clade
                |1={{clade
                  |1={{extinct}}[[Ichthyosauromorpha]][[File:Ichthyosaurus BW.jpg|80px]]
                  |2={{clade
                    |1={{extinct}}[[Sauropterygia]] [[File:Dolichorhynchops BW flipped.jpg|80px]]
                    |2={{extinct}}[[Thalattosauria]] [[File:Miodentosaurus BW.jpg|80px]]
                     }}
                   }}
                |2={{clade
                  |label1={{extinct}}[[Protorosauria]]
                  |1={{clade
                    |1={{extinct}}[[Protorosauridae]][[File:Protorosaurus BW.jpg|80px]]
                    |2={{clade
                      |1={{extinct}}[[Tanystropheidae]][[File:Macrocnemus BW.jpg|80px]]
                      |2={{clade
                        |1={{extinct}}[[Drepanosauromorpha]][[File:Megalancosaurus BW.jpg|80px]]
                        |2={{extinct}}[[Kuehneosauridae]][[File:Icarosaurus white background.jpg|80px]]
                         }}
                       }}
                     }}
                  |2={{clade
                    |1={{clade
                      |1={{extinct}}[[Allokotosauria]][[File:Trilophosaurus buettneri (flipped).jpg|80px]]
                      |2={{extinct}}[[Rhynchosaur]]ia[[File:Hyperodapedon BW2 white background.jpg|80px]]
                       }}
                    |2=[[Archosauriformes]]  ([[Crocodilia|crocodiles]], [[bird]]s, and their extinct relatives) <span style="{{MirrorH}}">[[File:Deinosuchus riograndensis.png|80px]]</span>
                     }}
                   }}
                 }}
               }}
             }}
           }}
         }}
      }}
   }}
}}

The following cladogram was found by Jenkins et al. (2025).<ref name="Jenkins2025">{{cite journal |last1=Jenkins |first1=Xavier A. |last2=Benson |first2=Roger B.J. |last3=Ford |first3=David P. |last4=Browning |first4=Claire |last5=Fernandez |first5=Vincent |last6=Dollman |first6=Kathleen |last7=Gomes |first7=Timothy |last8=Griffiths |first8=Elizabeth |last9=Choiniere |first9=Jonah N. |last10=Peecook |first10=Brandon R. |date=2025-08-28 |title=Evolutionary assembly of crown reptile anatomy clarified by late Paleozoic relatives of Neodiapsida |journal=Peer Community Journal |volume=5 |article-number=e89 |doi=10.24072/pcjournal.620 |doi-access=free }}</ref> Traditional [[Parareptilia|parareptiles]] are highlighted in orange:
{{clade
| label1='''Diapsida'''
| 1={{clade
| 1={{extinct}}[[Araeoscelidia]] [[File:Spinoaequalis schultzei reconstruction.jpg|80px]]
| 2={{clade
| bar1=orange
| 1={{extinct}}[[Bolosauridae]] [[File:Eudibamus BW.jpg|80px]]
| label2=[[Neoreptilia]]
| 2={{clade
| bar1=orange
| label1={{extinct}}[[Ankyramorpha]]
| 1={{clade
| 1={{extinct}}[[Acleistorhinidae]] [[File:Carbonodraco lundi.png|80px]]
| 2={{clade
| 1={{extinct}}[[Pareiasauromorpha]] [[File:Scutosaurus BW.jpg|80px]]
| 2={{extinct}}[[Procolophonoidea]] [[File:Sclerosaurus1DB.jpg|80px]]
}}
}}
| 2={{clade
| bar1=orange
| 1={{extinct}}[[Mesosauridae]] [[File:Mesosaurus BW.jpg|80px]]
| 2={{clade
| 1={{clade
| 1={{extinct}}''[[Cabarzia]]''
| 2={{clade
| 1={{extinct}}''[[Ascendonanus]]''
| 2={{extinct}}''[[Orovenator]]'' [[File:Orovenator.jpg|80px]]
}}
}}
| label2=[[Parapleurota]]
| 2={{clade
| bar1=orange
| 1={{extinct}}[[Millerettidae]] [[Image:Milleretta BW.jpg|80px]]
| label2=[[Neodiapsida]]
| 2={{clade
| 1={{extinct}}[[Younginidae]] [[File:Youngina capensis.png|80px]]
| 2={{clade
| 1={{extinct}}[[Tangasauridae]] [[File:Hovasaurus BW flipped.jpg|80px]]
| 2={{clade
| 1={{extinct}}[[Weigeltisauridae]] [[File:Weigeltisaurus_reconstruction.png|80px]]
| 2={{clade
| 1={{extinct}}''[[Claudiosaurus]]'' [[File:Claudiosaurus white background.jpg|80px]]
| 2=[[Sauria]] <span style="{{MirrorH}}">[[File:Deinosuchus riograndensis.png|80px]]</span>
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}

==See also==
* {{annotated link|Vertebrate paleontology}}
* {{annotated link|Synapsida}}
* {{annotated link|Anapsid}}
* {{annotated link|Euryapsida}}

==References==
{{Reflist}}

==External links==
{{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}}

 [[Category:Diapsids|01]]
[[Category:Reptile taxonomy]]
<!-- [[Category:Vertebrate unranked clades]] moved to Diapsida redirect -->
[[Category:Reptiles of the United States]]
[[Category:Extant Pennsylvanian first appearances]]
[[Category:Taxa named by Henry Fairfield Osborn]]