Mosasaurus is a genus of mosasaurs, carnivorous aquatic lizards. It existed during the Maastrichtian age of the late Cretaceous period, between about 70 and 66 million years ago, in western Europe and North America. Learn about Mosasaurus , a powerful marine reptile that ruled the ancient oceans. Discover its physical features, diet, behavior, and how it evolved from ancient lizards. Learn about the appearance, habitat, diet, reproduction, and threats of Mosasaurus , an extinct amphibious reptile that lived in the open ocean 70 to 66 million years ago. Discover 7 astonishing facts and FAQs about this ancient predator that was related to monitor lizards and had razor-sharp teeth.