Mesosaurus, meaning "middle lizard" is an extinct genus of reptile from the Early Permian of southern Africa and South America - Early Permian Period (299 million to 271 million years ago).
Mesosaurus was significant in providing evidence for the theory of continental drift, because its remains were found in southern Africa and Eastern South America two widely separated regions. As Mesosaurus was a coastal animal, and therefore less likely to have crossed the Atlantic Ocean, this distribution indicated that the two continents used to be joined together.