Plesiosaur

Plesiosaur, any member of a group of carnivorous ocean-dwelling reptiles that flourished during the Age of Reptiles, from the Late Triassic period to the end of the Cretaceous period, about 65 million years ago. Some plesiosaurs were more than 15 m (50 ft) long. Two major types of plesiosaur existed, one with a long neck and relatively small head, and the other with a short neck and a large head. In some species the large head accounted for about one-fourth of the animal's total length. The limbs of plesiosaurs were like flippers; the tail was short.