plesiosaurus plesiosaurus /ˌpliːsiːˈɔːrʌs/

noun

1. Extinct marine reptile with a small head on a long neck a short tail and four paddle-shaped limbs; of the Jurassic and Cretaceous  ( plesiosaur , plesiosaurus )
   extinct marine reptile with a small head on a long neck a short tail and four paddle-shaped limbs; of the Jurassic and Cretaceous