Plesiosaurus (Greek: πλησιος/plesios, near to+ σαυρος/sauros, lizard) is a genus of extinct... Plesiosaurus (Greek: πλησιος/plesios, near to+ σαυρος/sauros, lizard) is a genus of extinct, large marine sauropterygian reptile that lived during the early part of the Jurassic Period, and is...