Plesiosaur - A genus of marine reptiles (suborder Plesiosauria) of the Mesozoic of Europe and North America having a very long neck, a small head and limbs developed as paddles for swimming.

extinct marine reptile with a small head on a long neck a short tail and four paddle-shaped limbs; of the Jurassic and Cretaceous

A type of long-necked marine reptile

Plesiosaurs were flippered marine reptiles from the Mesozoic Era - they were not dinosaurs.

Plesiosaurs (IPA ) (Greek: plesios meaning 'near' or 'close to' and sauros meaning 'lizard') were carnivorous aquatic (mostly marine) reptiles. After their discovery, they were somewhat fancifully said to have resembled http://www.oceansofkansas.com/Snaketurtle.html "a snake threaded through the shell of a turtle", although they had no shell. The common name 'plesiosaur' is applied both to the 'true' plesiosaurs (Suborder Plesiosauroidea) and to the larger taxonomic rank of Plesiosauria, which includes both long-necked (elasmosaurs) and short-necked (polycotylid) forms.