Mesosauria

Article By:

Carroll, Robert L. Redpath Museum, McGill University, Montreal, Quebec, Canada.

Last reviewed:2014

DOI:https://doi.org/10.1036/1097-8542.416800

An order of extinct aquatic reptiles, also known as Proganosauria, of latest Carboniferous or earliest Permian time, about 2.8 × 10⁸ years ago. The best-known genus, Mesosaurus (see illustration), occurs in the Iratí bituminous shales of southern Africa. Geological evidence demonstrates that South America and Africa were part of a single land mass in the late Paleozoic, prior to the formation of the Atlantic Ocean. No other reptiles are known from contemporary beds on either continent. Like many aquatic reptiles, mesosaurs have a very long snout. The teeth are numerous and long, and appear very delicate. They may have served for filter feeding on soft-bodied invertebrates. The girdles and limbs are little modified for aquatic locomotion. The hands and feet are paddle-shaped. The tail is long and laterally compressed. The trunk ribs have the swollen form (pachystosis) characteristic of nothosaurs (aquatic reptiles of the Triassic) and sirenians, both of which show early stages in the adaptation of a formerly terrestrial group toward life in the water. Mesosaurs, an early offshoot of the Carboniferous “stem reptiles” or captorhinomorphs, were the first reptiles to invade marine waters, but apparently soon became extinct, leaving no descendants. See also: Reptilia

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