Early Permian period (299-280 mya)
Not to be confused with the similarly-spelled Mosasaurus, which is a different creature entirely.
Mesosaurus was one of the earliest aquatic reptiles, returning to the water only about 10-15 million years after the first true reptiles emerged in the late Carboniferous. About 1m long (3ft 3in), it lived in shallow coastal waters and hypersaline lagoons, and had long jaws full of needle-shaped teeth, probably preying on small fish and crustaceans.
Fossils of this animal were significant in providing evidence for the theory of “continental drift" in the mid 20th century. Found in both South America and southern Africa, but incapable of crossing the vast open ocean of the southern Atlantic, the presence of Mesosaurus in both locations suggested that the continents had once been joined.
Mesosaurus may also represent the earliest known example of live birth in the fossil record, with one specimen preserving a developing embryo.
Color palette used: “Cosmic Sins”