Mesosaur

Mesosaurus (meaning "middle lizard") is an extinct genus of aquatic reptile from the late Early Permian (Kungurian, ~275 million years ago) of southern Africa and South America. It is the only member of the family Mesosauridae and order Mesosauria. Two other genera of mesosaurs, Brazilosaurus and Stereosternum, were formerly recognised, but are now considered synonyms of Mesosaurus. Mesosaurus contains a single valid species, M. tenuidens. Mesosaurus represents one of the earliest lineages of aquatically adapted reptiles. It had many adaptations to a fully aquatic lifestyle. Mesosaurus lived around the shorelines of the Irati–Whitehill sea, an epicontinental sea that covered parts of southern Pangaea during the late Early Permian, likely feeding on small prey such as pygocephalomorph crustaceans. Mesosaurs have often been considered parareptiles, though the validity of "Parareptilia" has recently been brought into question. Recent studies regardless place mesosaurs as basal, non-diapsid reptiles.