Sauria

Sauria is the clade of diapsids containing the most recent common ancestor of Archosauria (which includes crocodilians and birds) and Lepidosauria (which includes squamates and the tuatara), and all its descendants.<ref>Gauthier, J. A., Kluge, A. G., & Rowe, T. (1988). The early evolution of the Amniota. The phylogeny and classification of the tetrapods, 1, 103–155.</ref> Since most molecular phylogenies recover turtles as more closely related to archosaurs than to lepidosaurs as part of Archelosauria, Sauria can be considered the crown group of diapsids, or reptiles in general.<ref>Template:Cite journal</ref> Depending on the systematics, Sauria includes all modern reptiles<ref name=":0">Template:Cite journal</ref> or most of them (including birds, a type of archosaur) as well as various extinct groups.<ref name=Li2018>Template:Cite journal</ref>

Sauria lies within the larger total group Sauropsida, which also contains various stem-reptiles which are more closely related to reptiles than to mammals.<ref name=":0" /> Prior to its modern usage, "Sauria" was used as a name for the suborder occupied by lizards, which before 1800 were considered crocodilians.

Systematics

Sauria was historically used as a partial equivalent for Squamata (which contains lizards and snakes).<ref>Template:Citation</ref> The redefinition to cover the last common ancestor of archosaurs and lepidosaurs was the result of papers by Jacques A. Gauthier and colleagues in the 1980s.<ref>Template:Citation</ref>

Genomic studies<ref>Template:Cite journal</ref><ref name="Crawford2014">Crawford, Nicholas G., et al. "More than 1000 ultraconserved elements provide evidence that turtles are the sister group of archosaurs." Biology letters 8.5 (2012): 783–786.</ref><ref name="Jarvis2014">Template:Cite journal</ref> and comprehensive studies in the fossil record<ref name="scaffold2013">Template:Cite journal</ref> suggest that turtles are closely related to archosaurs as part of Sauria, and not to the non-saurian parareptiles as previously thought. In a 2018 cladistic analysis, Pantestudines (turtles and close relatives) were placed within Diapsida but outside of Sauria.<ref name=Li2018/>

Synapomorphies

The synapomorphies or characters that unite the clade Sauria also help them be distinguished from stem-saurians in Diapsida or stem-reptiles in clade Sauropsida in the following categories based on the following regions of the body.<ref name=Pough2005>Pough, F. H., Janis, C. M., & Heiser, J. B. (2005). Vertebrate life. Pearson/Prentice Hall.</ref><ref>Laurin, Michel and Jacques A. Gauthier. 2011. Diapsida. Lizards, Sphenodon, crocodylians, birds, and their extinct relatives. Version 20 April 2011. http://tolweb.org/Diapsida/14866/2011.04.20 in The Tree of Life Web Project, http://tolweb.org/</ref><ref>Laurin, Michel and Jacques A. Gauthier. 2011. Autapomorphies of Diapsid Clades. Version 20 April 2011. http://tolweb.org/accessory/Autapomorphies_of_Diapsid_Clades?acc_id=465 in The Tree of Life Web Project, http://tolweb.org/</ref>

• Cephalad Region
  • Dorsal origin of temporal musculature
  • Loss of caniniform region in maxillary tooth row
  • External nares close to the midline
  • Postparietal absent
  • Squamosal mainly restricted to top of skull
  • The occipital flange of the squamosal is little exposed on the occiput
  • Anterior process of squamosal narrow
  • Quadrate exposed laterally
  • Unossified dorsal process of stapes
  • Stapes slender
• Trunk Region
  • Sacral ribs oriented laterally
  • Ontogenetic fusion of caudal ribs
  • Trunk ribs mostly single headed
• Pectoral Region
  • Cleithrum absent
• Pelvic Region
  • Modified ilium
• Limb Region
  • Tubular bone lost
  • Entepicondylar foramen absent
  • Radius as long as ulna
  • Small proximal carpals and tarsal
  • Fifth distal tarsal absent
  • Short and stout fifth or hooked metatarsal
  • Perforating foramen of manus lost

However, some of these characters might be lost or modified in several lineages, particularly among birds and turtles; it is best to see these characters as the ancestral features that were present in the ancestral saurian.<ref name="Pough2005"/>

Phylogeny

The cladogram shown below follows the most likely result found by an analysis of turtle relationships using both fossil and genetic evidence by M.S. Lee, in 2013. This study found Eunotosaurus, usually regarded as a turtle relative, to be only very distantly related to turtles in the clade Parareptilia.<ref name="scaffold2013"/>

The cladogram below follows the most likely result found by another analysis of turtle relationships, this one using only fossil evidence, published by Rainer Schoch and Hans-Dieter Sues in 2015. This study found Eunotosaurus to be an actual early stem-turtle, though other versions of the analysis found weak support for it as a parareptile.<ref name=pappochelys2015>Template:Cite journal</ref> Template:Clade

The cladogram below follows the analysis of Li et al. (2018). It places turtles within Diapsida but outside of Sauria (the Lepidosauromorpha + Archosauromorpha clade).<ref name=Li2018/> Template:CladeThe following cladogram was found by Simões et al. (2022):<ref>Template:Cite journal</ref>Template:Clade

External links

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