# Euryapsida

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{{Short description|Group of extinct reptiles}}
__NOTOC__
thumb|right|A euryapsid skull.
'''Euryapsida''' is a [polyphyletic](/source/polyphyletic) (unnatural, as the various members are not closely related) group of [sauropsids](/source/Sauropsida) that are distinguished by a single temporal fenestra, an opening behind the [orbit](/source/orbit_(anatomy)), under which the post-orbital and squamosal bones articulate. They are different from [Synapsida](/source/Synapsida), which also have a single opening behind the orbit, by the placement of the fenestra. In synapsids, this opening is below the articulation of the post-orbital and squamosal bones. It is now commonly believed that euryapsids (particularly [sauropterygia](/source/sauropterygia)ns) are in fact [diapsid](/source/diapsid)s (which have two fenestrae behind the orbit) that lost the lower temporal fenestra. Euryapsids are usually considered entirely extinct, although [turtle](/source/turtle)s might be part of the sauropterygian clade<ref>{{Cite journal |last=Lee |first=M. S. Y. |date=2013 |title=Turtle origins: insights from phylogenetic retrofitting and molecular scaffolds |journal=Journal of Evolutionary Biology |language=en |volume=26 |issue=12 |pages=2729–2738 |doi=10.1111/jeb.12268|doi-access=free |pmid=24256520 }}</ref> while other authors disagree.<ref name=":0">{{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> Euryapsida may also be a synonym of Sauropterygia ''sensu lato''.<ref name=":1">{{Cite journal |last=Rieppel |first=Olivier |date=1989-01-04 |title=A new pachypleurosaur (Reptilia: Sauropterygia) from the Middle Triassic of Monte San Giorgio, Switzerland |url=https://royalsocietypublishing.org/doi/10.1098/rstb.1989.0001 |journal=Philosophical Transactions of the Royal Society of London. B, Biological Sciences |language=en |volume=323 |issue=1212 |pages=1–73 |doi=10.1098/rstb.1989.0001 |bibcode=1989RSPTB.323....1R |issn=0080-4622|url-access=subscription }}</ref>

The [ichthyosaur](/source/Ichthyosauria)ian skull is sometimes described as having a ''metapsid'' (or ''parapsid'') condition instead of a truly euryapsid one. In ichthyosaurs, the squamosal bone is never part of the fenestra's margin.<ref>{{Cite journal |last=Maisch |first=M. |date=2010 |title=Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art |journal=Palaeodiversity |volume=3 |pages=151–214|s2cid=87979321 |language=en}}</ref> Parapsida was originally a taxon consisting of ichthyosaurs, squamates, protorosaurs, araeoscelidans and [pleurosaurs](/source/Pleurosauridae).<ref name=":1" />

Historically, a variety of reptiles with upper fenestrae, either alone or with a lower emargination, have been considered euryapsid or parapsid, and to have had their patterns of fenestration originate separately from those of diapsids. This includes [araeoscelida](/source/araeoscelida)ns, [mesosaur](/source/mesosaur)s, [squamate](/source/squamate)s, [pleurosaurid](/source/pleurosaurid)s,<ref>{{Cite book |last=Williston |first=Samuel Wendell |title=Osteology of the Reptiles |year=1925}}</ref> [weigeltisaurid](/source/weigeltisaurid)s, [protorosaur](/source/protorosaur)s, and [trilophosaur](/source/trilophosaur)s.<ref>{{Cite book |last=Romer |first=Alfred Sherwood |title=Osteology of the Reptiles |year=1956}}</ref><ref>{{Cite book |last=Romer |first=Alfred Sherwood |title=Vertebrate Paleontology |publisher=University of Chicago Press |year=1966 |edition=3rd |location=Chicago |language=en}}</ref> With the exception of mesosaurs, which only have the lower temporal opening, all of these are universally agreed to be diapsids which either secondarily closed the lower opening (araeoscelids, trilophosaurs) or lost the lower bar (squamates, pleurosaurs, protorosaurs).

Euryapsida was proposed by [Edwin H. Colbert](/source/Edwin_H._Colbert) as a substitute for the earlier term '''Synaptosauria''', originally created by [Edward D. Cope](/source/Edward_Drinker_Cope) for a taxon including sauropterygians, turtles and rhynchocephalians. [Baur](/source/Georg_Baur) removed the rhynchocephalians from Synaptosauria and [Williston](/source/Samuel_Wendell_Williston) later resurrected the taxon, including only Sauropterygia ([Nothosaur](/source/Nothosaur)ia and [Plesiosaur](/source/Plesiosaur)ia) and [Placodontia](/source/Placodontia) in it.<ref name=":1" />

thumb|right|A parapsid skull.
The terms '''Enaliosauria''' and '''Halisauria''' have also been used for a taxon including ichthyosaurs and sauropterygians.<ref>{{Cite encyclopedia|url=https://www.merriam-webster.com/dictionary/Enaliosauria|title=Enaliosauria|dictionary=Merriam-Webster|access-date=22 December 2021}}</ref><ref>{{Cite book |last=Haeckel |first=Ernst |title=Die systematische Phylogenie (Dritter Theil/Systematische Phylogenie der Wirbelthiere (Vertebrata)) |publisher=Georg Reimer |year=1895 |volume=3}}</ref>

Some 21st century studies have found that ichthyosaurs, [thalattosaurs](/source/Thalattosauria) and sauropterygians were close relatives, either as [stem-archosaurs](/source/Archosauromorpha)<ref name=":0" /><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 |editor2-last=Perry |editor2-first=George H |editor3-last=Benton |editor3-first=Michael |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 |doi-access=free |issn=2050-084X |pmc=10499374 |pmid=37551884}}</ref> or as stem-saurians.<ref>{{Cite journal |last1=Neenan |first1=James M. |last2=Klein |first2=Nicole |last3=Scheyer |first3=Torsten M. |date=2013-03-27 |title=European origin of placodont marine reptiles and the evolution of crushing dentition in Placodontia |url=https://www.nature.com/articles/ncomms2633 |journal=Nature Communications |language=en |volume=4 |issue=1 |page=1621 |doi=10.1038/ncomms2633 |pmid=23535642 |bibcode=2013NatCo...4.1621N |issn=2041-1723}}</ref><ref>{{Cite journal |last1=Jiang |first1=Baoyu |last2=He |first2=Yiming |last3=Elsler |first3=Armin |last4=Wang |first4=Shengyu |last5=Keating |first5=Joseph N. |last6=Song |first6=Junyi |last7=Kearns |first7=Stuart L. |last8=Benton |first8=Michael J. |date=2023 |title=Extended embryo retention and viviparity in the first amniotes |journal=Nature Ecology & Evolution |language=en |volume=7 |issue=7 |pages=1131–1140 |doi=10.1038/s41559-023-02074-0 |issn=2397-334X |pmc=10333127 |pmid=37308704|bibcode=2023NatEE...7.1131J }}</ref>

==See also==
* [Anapsid](/source/Anapsida)
* [Diapsid](/source/Diapsida)
* [Synapsida](/source/Synapsida)

==References==
{{reflist}}
{{Sauropsida|N.}}
Category:Polyphyletic groups
Category:Prehistoric marine reptiles
Category:Prehistoric reptile taxonomy

{{paleo-reptile-stub}}

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Adapted from the Wikipedia article [Euryapsida](https://en.wikipedia.org/wiki/Euryapsida) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Euryapsida?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.