Mesosaurus fossil. Hands holding rock containing a fossil of the extinct aquatic reptile Mesosaurus tenuidens. This anapsid reptile existed in the Permian period and was one of the first reptiles to return to water, where its amphibian ancestors came from. The discovery of Mesosaurus fossils in deposits in both South America and southern Africa was significant in proving the theory of continental drift. Photographed in Spitzkoppe, Namibia, Africa.