Sauropsid
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Subclass Anapsida
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Sauropsida is an amniote clade that includes all recent and all or almost all extinct reptiles (excluding the Synapsida), and birds.
The terms Sauropsida ("Lizard Faces") and Theropsida ("Beast Faces") were coined in 1916 by E.S. Goodrich to distinguish between lizards, birds, etc on the one hand (Sauropsida) and mammal-like reptiles and mammals (Theropsida) on the other. This division is supported by the nature of the hearts and blood-vessels in each group, and also other features such as the structure of the forebrain. According to Goodrich both lineages evolved from an earlier stem group, the Protosauria ("First Lizards") which included some Paleozoic amphibians as well as early reptiles.
In 1956 D.M.S. Watson observed that the first two groups diverged very early in reptilian history, and so he divided Goodrich's Protosauria among them. He also reinterpreted the Sauropsida and Theropsida to exclude birds and mammals respectively. Sauropsida thus came to refer to the Procolophonia, Eosuchia, Millerosauria, Chelonia (turtles), Squamata (lizards and snakes), Rhynchocephalia, Crocodylia, Thecodontia, Dinosaurs, Pterosaurs, Ichthyosaurs, and Sauropterygia; while the Theropsida (=Synapsida) included the Pelycosaurs and the Therapsida (mammal-like reptiles).
This classification supplemented, but was never as popular, as the classification of the Reptiles (for example in Romer's classic Vertebrate Paleontology) into four sub-classes according to the positioning of temporal fenestrę (holes) on the back of the skull. Those divisions are:
- Anapsida - no fenestrę
- Synapsida - low fenestrę (beneath the postorbital and squamosal bones)
- Euryapsida - high fenestrę (above the postorbital and squamosal)
- Diapsida - two fenestrę
All of the above but Synapsida fall under "Sauropsida".
In the current cladistic based system, the Linnean classification of the Class Reptilia in terms of four sub-classes has been replaced. Euryapsida is considered either a subgroup of Diaspida or rejected altogether. "Sauropsid" (as a monophyletic clade) is retained to refer to all non-synapsid amniotes (or sometimes just replaced by "Reptilia" even though this group includes birds). The term "Theropsida" is replaced by Synapsida, which now refers to both the old subclass Synapsida and the mammals. In the new (2004) edition of his textbook, Dr Michael Benton uses the term "Class Sauropsida" to refer to all non-synapsid reptiles.
External links
- Tree of Life (http://tolweb.org/tree?group=Amniota&contgroup=Terrestrial_Vertebrates) Describes the early amniote clades
- University of Bristol (http://palaeo.gly.bris.ac.uk/benton/vertclass.html) Taxonomic hierarchy of the vertebrates, according to Benton 2004
References
- Benton, M. J. (2004), Vertebrate Paleontology, 3rd ed. Blackwell Science Ltd
- Colbert, E.H. (1969), Evolution of the Vertebrates, 2nd ed., John Wiley and Sons Inc.
- Goodrich, E.S. (1916). On the classification of the Reptilia. Proceedings of the Royal Society of London 89B: 261–276.
- Romer, A.S., Vertebrate Paleontology University of Chicago Press, 1933; 3rd ed. 1966.
- Watson, D.M.S. (1957). On Millerosaurus and the early history of the sauropsid reptiles. Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences, 1957, V.240, N.673, P.325-400.ca:Sauropsida