Not technically a dinosaur, Mosasaurus was a massive aquatic reptile closely related to modern monitor lizards. As an apex predator at the top of the food chain, it ate whatever fit in its mouth: sharks, turtles, birds and even other mosasaurs.

Built long and sleek, Mosasaurus had a tail as long as its body and over 100 vertebrae in its spine. When hunting, it could thrust itself rapidly through the water by sweeping its tail from side to side.