Sauria Explained

Sauria is the clade 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.[1] 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.[2] Depending on the systematics, Sauria includes all modern reptiles[3] or most of them (including birds, a type of archosaur) as well as various extinct groups.[4]

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

Systematics

Genomic studies[5] [6] [7] and comprehensive studies in the fossil record[8] suggest that turtles are closely related to archosaurs, not to the pre-Saurian parareptiles as previously thought. In a 2018 cladistic analysis, Pantestudines (turtles and close relatives) were placed within Diapsida but outside of Sauria.[4]

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.[9] [10] [11]

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.[9]

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.[8]

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.[12]

The cladogram below follows the analysis of Li et al. (2018). It places turtles within Diapsida but outside of Sauria (the Lepidosauromorpha + Archosauromorpha clade).[4] The following cladogram was found by Simões et al. (2022):[13]

Notes and References

  1. 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.
  2. Simões . Tiago R. . Kammerer . Christian F. . Caldwell . Michael W. . Pierce . Stephanie E. . 2022-08-19 . Successive climate crises in the deep past drove the early evolution and radiation of reptiles . Science Advances . en . 8 . 33 . eabq1898 . 10.1126/sciadv.abq1898 . 2375-2548 . 9390993 . 35984885. 2022SciA....8.1898S .
  3. Ezcurra . M. D. . Scheyer . T. M. . Butler . R. J. . 2014 . The origin and early evolution of Sauria: reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence . PLOS ONE . 9 . 2 . e89165 . 10.1371/journal.pone.0089165 . 3937355 . 24586565 . free. 2014PLoSO...989165E .
  4. Li . Chun . Fraser . Nicholas C. . Rieppel . Olivier . Wu . Xiao-Chun . August 2018 . A Triassic stem turtle with an edentulous beak . Nature . en . 560 . 7719 . 476–479 . 10.1038/s41586-018-0419-1 . 30135526 . 2018Natur.560..476L . 52067286 . 0028-0836.
  5. Wang. The draft genomes of soft-shell turtle and green sea turtle yield insights into the development and evolution of the turtle-specific body plan. Nature Genetics. 27 March 2013. 45. 701–706. 701–6. 10.1038/ng.2615. Zhuo. 23624526. 4000948.
  6. 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.
  7. Jarvis . E.D. . etal . 2014 . Whole-genome analyses resolve early branches in the tree of life of modern birds . Science . 346 . 6215. 1320–1331 . 10.1126/science.1253451 . 25504713 . 4405904. 2014Sci...346.1320J .
  8. 10.1111/jeb.12268. Turtle origins: Insights from phylogenetic retrofitting and molecular scaffolds. Journal of Evolutionary Biology. 26. 12. 2729–2738. 2013. Lee . M. S. Y.. 24256520. 2106400. free.
  9. Pough, F. H., Janis, C. M., & Heiser, J. B. (2005). Vertebrate life. Pearson/Prentice Hall.
  10. 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/
  11. 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/
  12. Schoch . Rainer R. . Sues . Hans-Dieter . A Middle Triassic stem-turtle and the evolution of the turtle body plan . . 523. 7562. 584–587. 10.1038/nature14472 . 24 June 2015 . 26106865. 2015Natur.523..584S . 205243837 .
  13. Simões . Tiago R. . Kammerer . Christian F. . Caldwell . Michael W. . Pierce . Stephanie E. . 2022-08-19 . Successive climate crises in the deep past drove the early evolution and radiation of reptiles . Science Advances . en . 8 . 33 . eabq1898 . 2022SciA....8.1898S . 10.1126/sciadv.abq1898 . 2375-2548 . 9390993 . 35984885.

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