Plesiosaurus

Plesiosaurus , genus of extinct predatory marine reptiles that arose in the Triassic period of geologic time and continued into the Jurassic and Cretaceous periods. Plesiosaurs became extinct at the close of the Mesozoic era. Fossilized skeletons of them have been found in North America, Europe, and Australia. The plesiosaur had a small, short head, a long, snakelike neck, a broad, solid body, and a short tail. It had sharp interlocking teeth, and its four paddlelike legs were similar to those of a marine turtle. In total length, Plesiosaurus ranged from 10 to 60 ft (3-18 m). The term plesiosaur is sometimes applied more generally to all forms in the order Sauropterygia, which produced two lines of marine reptiles. The Plesiosaurus is an example of one trend. The other group evolved into forms possessing short necks and gigantic skulls; the most extreme example, that of the Kronosaurus, had the largest known reptile skull, reaching 9 ft (2.7 m) in length. Plesiosaurs are classified in the phylum Chordata , subphylum Vertebrata, class Reptilia, order Sauropterygia.

plesiosaurus one of a genus of extinct marine reptiles. XIX. f. Gr. plēsíos near + saúros lizard.

Plesiosauroidea (plesiosaurs) Suborder of aquatic reptiles which enter the fossil record in the late Triassic, and which are common in many Jurassic and Cretaceous sediments. In appearance they were likened by Buckland to ‘a snake strung through the body of a turtle’, and some grew up to 15 m in length. There were also short-necked types, as well as the swannecked. The former are defined as the superfamily Plesiosauroidea (e.g. Plesiosaurus and Muraenosaurus), the latter as the superfamily Pliosauroidea (e.g. Pliosaurus and Trinacromerum), the two superfamilies making up the suborder.