Anatomy: These streamlined reptiles were roughly 7.6 feet (2.3 m) long and may have weighed about 200 pounds (90 kg). They had four wide, paddle-shaped flippers, and a tapered body. They had many long, sharp, conical teeth in long jaws. The head was relatively small.

Fossils: Plesiosaurus was first found by the famous fossil hunter Mary Anning in 1821 and was named by H.T. De La Beche and William D. Conybeare later that year. The type species is P. dolichodeirus. Plesiosaurus fossils have been found in England and Germany.