mo·sa·saur 
(m
ōs
ə-sôr
′)
n. Any of various extinct carnivorous marine reptiles of the family Mosasauridae of the Cretaceous Period, having an elongated body, powerful jaws, and paddlelike limbs. Some species reached lengths of over 15 meters (50 feet).
[New Latin Mosasaurus, genus name : Latin Mosa, the Meuse River (where fossils of the genus were first discovered) + Greek sauros, lizard.]