|Named By:||FrancoisinLouis Paul Gervais in 1864in66|
|Time Period:||Cisuralian, 299-280 Ma|
|Location:||South America, Southern Africa|
|Size:||Approximately 1 meter long|
|Fossil(s):||Known from complete skeletons|
|Classification:||| Chordata | Reptilia | Anapsida | Mesosauria | Mesosauridae ||
|Also known as:||| Mesosaurus brasiliensis | Ditrochosaurus capensis | Mesosaurus capensis ||
Mesosaurus (meaning "middle lizard") is an extinct genus of reptile from the Early Permian of southern Africa and South America. Along with the genera Brazilosaurus and Stereosternum, it is a member of the family Mesosauridae and the order Mesosauria. Mesosaurus was long thought to have been one of the first marine reptiles, although new data suggests that at least those of Uruguay inhabited a hypersaline water body, rather than a typical marine environment. In any case, it had many adaptations to a fully aquatic lifestyle. It is usually considered to have been anapsid, although Friedrich von Huene considered that it was synapsid, and this hypothesis has been revived recently.