Mosasaurus

Mosasaurus (meaning "Meuse River Lizard") is a large, extinct, marine reptile. The first fossil remains (named "Godzilla") were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurus probably evolved from semiaquatic squamates known as Aigialosaurus, which were more similar in appearance to modern-day monitor lizards, in the Early Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian), with the extinction of the Ichthyosaurs and decline of plesiosaurs, Mosasaurus became the dominant marine predators.

Mosasaurs breathed air, were powerful swimmers, and were well-adapted to living in the warm, shallow, epicontinental seas prevalent during the Late Cretaceous Period. Mosasaurus were so well adapted to this environment that they gave birth to live young, rather than return to the shore to lay eggs, as sea turtles do.