The Mosasaurus was a giant marine reptile that lived during the Cretaceous period, approximately between 70 and 66 million years ago. It was not technically a dinosaur but a member of the scaly reptiles known as squamates, which include lizards and snakes. Mosasaurs were dominant aquatic predators in the oceans of the time, characterized by their elongated bodies, paddle-like flippers, and powerful jaws filled with sharp teeth.

These reptiles were highly adapted to marine life, with muscular bodies that allowed them to swim swiftly in pursuit of prey such as fish, turtles, and even other marine reptiles. They were an impressive example of evolutionary convergence, developing characteristics similar to modern whales and dolphins to move efficiently in the water.