Mesosaurus fossils are found in hard, solid rock on two different plates of Earths surface: the South American and African Plates. The fossils are found in South America, especially Brazil, and in southern Africa. Mesosaurus lived during the Early Permian Period and was an early aquatic relative of reptiles that lived in freshwater lakes and ponds. The geographic distribution of Mesosaurus fossils provided paleontological evidence corroborating the hypothesis that the continents of the Southern Hemisphere were once joined. Therefore, the land where Mesosaurus fossils are found was once part of a larger landmass, which later separated due to plate tectonics.