Mosasaur

A mosasaur (Mosasaurus, Tylosaurus, Platecarpus, and other species) was not a dinosaur, but rather an ocean-dwelling reptile related to varanids like monitor lizards. These predators dominated the oceanic food chain during the Late Cretaceous period. Mosasaurs ranged in size up to 10 meters or so, with a body form similar to that of a crocodile although streamlined for fast swimming in marine waters.

External link

specimen mosasaur species at University of Texas Memorial Museum.