More formally known as Mesosaurus brasiliensis, here’s a water lizard fossil on display at the Burke Museum of Natural History and Culture in Seattle, Washington:
Mesosaurus was one of the first aquatic reptiles, returning to the water around 360 million years ago. As a result, it had four legs with webbed feet, but the structure of its elbows and ankles would have limited its mobility out of the water. It was much like a small (up to 1 meter / 3.3 feet long), early crocodile.
Mesosaurus’ significance, though, goes well beyond its role in its environment. Since in life Mesosaurus was constrained to coastal environments, but its fossils have been found in both southern Africa and southeastern South America, it provided early evidence for the theory of continental drift (now explained by the geological mechanism of plate tectonics).