GIANT SEA REPTILES OF THE DINOSAUR AGE at the Natural History Museum of Los Angeles County, CA

Mosasaur skeleton from Kansas at the Natural History Museum of Los Angeles County

Several years ago, when I was researching my book about giant sea reptiles, I visited the Natural History Museum of Los Angeles County in Exposition Park to view the fossil skeleton of a mosasaur. The huge mouth and sharp teeth made me glad that I wasn't meeting this creature in real life! In the late Cretaceous Period, about 80 million years ago, these huge reptiles were the supreme predators of the sea. But, like the dinosaurs, mosasaurs became extinct 65 million years ago. We know about them from their fossil remains.

Fossils of mosasaurs have been found all over the world, including Antarctica. A recent discovery in Hungary reveals that mosasaurs lived in both freshwater and saltwater. They swam in North America’s inland sea, and their fossils are especially numerous in Kansas and South Dakota. The largest known species, Tylosaurus, grew to be up to 50 feet long and weighed up to 11 tons.

Mosasaurs were excellent swimmers and propelled themselves through the water with a side-to-side motion of their long tails. Most of them ambushed their prey, making a swift attack and catching it by surprise. Bite marks on fossil nautiloids show that they were preyed upon by sea reptiles like mosasaurs.

Chambered nautiluses are still swimming in the ocean today.

Mosasaurs probably ate anything they could find, including other mosasaurs. The preserved stomach contents of a Tylosaurus found in South Dakota contains the remains of a smaller mosasaur, a bird, a fish, and what may have been a shark.

Mosasaurs, along with the icthyosaurs and plesiosaurs, also extinct, were the largest reptiles ever known to swim the Earth’s oceans. They are part of the amazing diversity of life during the Dinosaur Age.

You can read more about these fascinating animals in my book Giant Sea Reptiles of the Dinosaur Age, illustrated with beautiful water color paintings by Laurie Caple.