The mosasaurs were one of the success stories of the late Cretaceous period. The largest known mosasaur is Hainosaurus, which could reach 17 metres in length. Giant mosasaurs were the top predator in the sea and were widespread across the world.
Much of their day would have been spent swimming slowly near the seabed looking for suitable prey to attack. Their diet consisted of slow moving animals like ammonites, birds and turtles but they would also tackle larger and swifter prey, such as sharks and plesiosaurs, when the opportunity arose.
As the mosasaurs were not fast swimmers they would have stalked their prey using natural cover provided by seaweed and rocks. Only when the prey was within striking range would the mosasaur propel itself forward. Being caught in a mosasaurís jaws meant almost certain death.
Although giant mosasaurs were the top predators in the sea, they were still vulnerable to attack. One mosasaur fossil bears the marks of a shark bite in its spine.