Mesosauria (class Reptilia, subclass Anapsida) An order of reptiles that comprises one family, the Mesosauridae. The mesosaurs are known only from late Carboniferous or early Permian rocks in S. America and S. Africa. They were adapted to life in fresh water, lightly built, and up to 1 m in length.

Mesosauria Order of anapsid reptiles, with just one family, the Mesosauridae. The mesosaurs (e.g. Mesosaurus) are known only from late Carboniferous or early Permian rocks in S. America and S. Africa. They were adapted to life in fresh water, lightly built, and up to one metre in length.