Sauropsid

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Sauropsid

Eastern Water dragon, Physignathus lesueurii
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Superclass: Tetrapoda
(unranked) Amniota
Class: Sauropsida/ Reptilia
Clades

Subclass Anapsida
Subclass Diapsida

Infraclass Lepidosauromorpha
Infraclass Archosauromorpha

Sauropsids are a diverse group of egg-laying vertebrate animals. The Sauropsida includes all modern and most extinct " reptiles" (excluding Synapsids). Living sauropsids include lizards, snakes turtles, and crocodiles. Extinct sauropsids include dinosaurs, pterosaurs, plesiosaurs, Ichthyosaurs, and many others.

History of the Term "Sauropsida"

The terms Sauropsida ("Lizard Faces") and Theropsida ("Beast Faces") were coined in 1916 by E.S. Goodrich to distinguish between lizards, birds, and their relatives on 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 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, Cheloniana (turtles), Squamata (lizards and snakes), Rhynchocephalia, Crocodilia, 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 (according to Romer's classic Vertebrate Paleontology) into four sub-classes according to the positioning of temporal fenestrae, openings in the sides of the skull behind the eyes. Those divisions are:

  • Anapsida - no fenestrae
  • Synapsida - one low fenestra (beneath the postorbital and squamosal bones)
  • Euryapsida - one high fenestra (above the postorbital and squamosal)
  • Diapsida - two fenestrae

All of the above but Synapsida fall under "Sauropsida".

Sauropsida versus Reptilia

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.

Taxonomy

  • Amniota
  • CLASS SAUROPSIDA
    • Subclass Anapsida
      • Family Mesosauridae (Extinct)
      • Family Millerettidae (Extinct)
      • Family Bolosauridae (Extinct)
      • Family Procolophonidae (Extinct)
      • Family Pareiasauridae (Extinct)
      • Order Testudines ( Chelonia)
    • Family Captorhinidae (Extinct)
    • *Family Protorothyrididae (Extinct)
    • Subclass Diapsida
      • Order Araeoscelidia (Extinct)
      • Family Weigeltisauridae (Extinct)
      • Order Younginiformes (Extinct)
      • Infraclass Ichthyosauria (Extinct)
      • Infraclass Lepidosauromorpha
        • Superorder Sauropterygia (Extinct)
          • Order Placodontia (Extinct)
          • Order Nothosauroidea (Extinct)
          • Order Plesiosauria (Extinct)
        • Superorder Lepidosauria
          • Order Sphenodontida
          • Order Squamata
      • Infraclass Archosauromorpha
        • Family Trilophosauridae (Extinct)
        • Family Rhynchosauridae (Extinct)
        • Order Prolacertiformes (Extinct)
        • Family Proterosuchidae (Extinct)
        • Family Erythrosuchidae (Extinct)
        • Family Euparkeriidae (Extinct)
        • Family Phytosauridae (Extinct)
        • Family Ornithosuchidae (Extinct)
        • Family Stagonolepididae (Extinct)
        • Family Rauisuchidae (Extinct)
        • Family Poposauridae (Extinct)
        • Superorder Crocodylomorpha
          • Family Saltoposuchidae (Extinct)
          • Family Sphenosuchidae (Extinct)
          • Order Crocodylia
        • Scleromochlus (Extinct)
        • Order Pterosauria (Extinct)
          • Suborder Rhamphorhynchoidea
          • Suborder Pterodactyloidea
        • Lagerpeton (Extinct)
        • Marasuchus (Extinct)
        • Superorder Dinosauria