Fossilised mosasaur teeth. The mosasaur was a large marine reptile that inhabited seas throughout the world during the Cretaceous period (145-65 million years ago). Mosasaurs fed mostly on molluscs and sea urchins, but were not unaccustomed to eating larger creatures such as sharks. Because of their flexible double-hinged jaw, used to swallow their prey whole, and their double row of sharp teeth, they are thought to have shared the same ancestor as snakes. However, mosasaurs are unusual in that they gave birth to live young rather than laying eggs. Fossil found in Khouriga, Morocco.