1. Extinct marine reptile of the Mesozoic era, characterized by a small head on a long neck, short tail, and four paddle-shaped limbs
   "The plesiosaurus was well-adapted for swimming in prehistoric oceans";
   - plesiosaur

Derived forms: plesiosauruses

Type of: archosaur, archosaurian, archosaurian reptile

Part of: genus Plesiosaurus

Encyclopedia: Plesiosaurus