View source for Sauropsid

{{Taxobox
| name = Sauropsids
| fossil_range = [[Pennsylvanian]] &ndash; Recent
| image =
| image_width
| image_caption= Eastern [[Water dragon]], ''Physignathus lesueurii''
| regnum = [[Animal]]ia
| phylum  = [[Chordate|Chordata]]
| subphylum = [[Vertebrate|Vertebrata]]
| superclassis = [[Tetrapod]]a
| unranked subclassis = [[Amniota]]
| unranked ordo = '''Sauropsida'''
| classis_authority = [[Edwin Stephen Goodrich|Goodrich]], 1916
| subdivision_ranks = [[Clades]]
}}

'''Sauropsids''' are a group of land [[vertebrate]]s which includes all existing [[reptile]]s and [[bird]]s and their [[fossil]] [[ancestor]]s. 

They are one of the two groups which evolved from egg-laying [[amniote]]s in the first part of the [[Carboniferous]] period.<ref name=Early>Gauthier J.A; Kluge A.G & Rowe T. 1988. The early evolution of the Amniota. pp103–155 in Michael J. Benton (ed) ''The phylogeny and classification of the tetrapods'', Volume 1: Amphibians, Reptiles, Birds. ''Systematics Association'', Special vol 35A. Clarendon Press, Oxford.</ref><ref>Gauthier J.A. 1994. The diversification of the amniotes. In D.R. Prothero and R.M. Schoch (eds) ''Major features of vertebrate evolution''. 129-159. Knoxville, Tennessee: The Paleontological Society.</ref><ref>Laurin M. & Gauthier J.A. 1996. [http://tolweb.org/Amniota/14990 Amniota, mammals, reptiles (turtles, lizards, ''Sphenodon'', crocodiles, birds) and their extinct relatives]. Version 01 January 1996. The Tree of Life Web Project.</ref>

The [[synapsid]]s are the other group which evolved from amniotes. They gave rise, eventually, to the [[mammal]]s.

Living sauropsids include [[lizard]]s, [[snake]]s, [[turtle]]s, [[crocodile]]s, and [[bird]]s. [[Extinction|Extinct]] sauropsids include non-avian [[dinosaur]]s, [[pterosaur]]s, [[plesiosaur]]s, [[ichthyosaur]]s, and many others.

==Origin of tetrapods==
More or less, the evolution of tetrapods has taken this course:
*[[Sarcopterygii]]
**[[Coelacanthimorpha]] ([[Coelacanth]]s)
**[[Dipnoi]] ([[lungfish]])
***[[Tetrapodomorpha]]
The earlies tetrapods lived in water.<ref name="Jenny">[[Jennifer Clack|Clack, Jennifer]] 2012. ''Gaining ground: the origin and early evolution of tetrapods''. 2nd ed, Bloominton, Indiana: Indiana University Press. {{ISBN|978-0-253-35675-8}}, ({{Google books|6Ztrhm8uLQ0C }})</ref> Clear fossil tetrapod [[Animal tracks|tracks]] from the mid-[[Devonian]] predate previous tetrapod records by 18 million years.<ref>Janvier, Phillipe and Clément, Gaël 2010. Muddy tetrapod origins. ''Nature'' '''463''', p40.</ref>

Nine [[genera]] of [[Devonian]] tetrapods have been described. These earliest tetrapods were not terrestrial. They lived in [[swamp]]y habitats like shallow [[wetlands]], coastal [[lagoons]], [[brackish]] [[river delta]]s, and even shallow [[Marine biology|marine]] [[sediment]]s.

===Romer's gap===
Between the lobe-finned fish tetrapods and the first [[amphibia]] and [[amniote]]s in the Middle [[Carboniferous]] lies a gap of 30 million years, with few satisfactory tetrapod fossils. This is "Romer's gap".<ref>Romer A.S. 1949. ''The vertebrate body.'' Saunders, Philadelphia. 2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970</ref> Some new fossils were found in the 1990s, such as ''[[Pederpes]]'', right in the middle of the Romer Gap. The gap still obscures the details of the tetrapod transition.

Sometime, in the later Devonian or earliest Carboniferous, the fishapods became mainly land-based. One group of them kept their link to the water, and always laid their eggs in water. They became the [[amphibian]]s. The others evolved a way of laying eggs on land. They were the [[amniotes]], whose key innovation was the [[cleidoic egg]].

Sometime in the middle or lower Carboniferous, the amniotes split into two lines. One line lead to the reptiles of all kinds, and we call that the Sauropsida. The other line led eventually to the mammals, and we call that the Synapsida. It is not right to say "mammals evolved from reptiles" because both groups derived from early amniotes. In any event, modern reptiles are vastly different from modern mammals.<ref>Goodrich E.S. 1930. ''Studies on the structure and development of vertebrates''. Macmillan, London. xxx+837p, 754 figures. One of the great works of vertebrate comparative anatomy.</ref> Both groups have evolved for over 300 million years from the early amniotes.

==Tetrapods==
*Land-dwelling tetrapods
**[[Amphibians]] > amniota and present-day amphibians
**[[Amniota]]
***'''Sauropsida''' > present-day [[reptile]]s and [[bird]]s
***[[Synapsida]] > present-day [[mammal]]s

==References==
{{Reflist}}

[[Category:Reptiles| ]]