Cotylosauria

a subclass of the most ancient primitive, extinct reptiles, which existed from the middle of the Carboniferous period to the Triassic period. Their size varied from small insectivorous procolophons and medium-sized predators (including aquatic animals) to large herbivorous pareiasaurs. Most members of the subclass retained many primitive characteristics inherited from amphibians: a skull without temporal depression but with a well-developed sincipital opening, palatines, amphicoelous vertebrae, a very short cervical section of the spine, and short and massive bones of the extremities and their girdles. Many Cotylosauria remains have been found in North America, southern Africa, and the European USSR. The remains are used as index forms in geology.