Mesosaurus is an extinct genus of anapsid reptile from the Early Permian of southern Africa and South America. It is a member of the family Mesosauridae and the order Mesosauria. Mesosaurus was one of the first marine reptiles and had fully adapted to a aquatic lifestyle.
Mesosaurus was one of the first reptiles to return to the water. It was around 1 meter ( 3.3 ft ) long.