The first Mosasaurus fossil was collected in 1764 in the Netherlands. Nothing like it had been seen before, and so the first people to examine it weren’t sure what it was - it was thought to be a fish, a whale, or possibly a crocodile. Eventually, paleontologists studied them more closely, and realized that these were fossils of an enormous lizard similar to modern monitor lizards.

Mosasaurus resembles monitor lizards like the famous Komodo dragon in having a large head and long jaws full of long sharp teeth, and a long flexible tail. However, unlike the Komodo dragon, it has paddles rather than legs that were adapted for swimming, as this Mosasaurus toy reflects. Mosasaurus used its tail to propel itself through the water, and its paddles for steering. It was a large predator (more than 50 feet in length) that ate fish, turtles, ammonites, as well as plesiosaurs and other mosasaurs.