Mosasaurus: The giant of the Late Cretaceous seas

Mosasaurus is the rightful "ocean ruler" of the museum's sea gallery. It lived in the Late Cretaceous oceans and was a large marine reptile. First, it is worth repeating: Mosasaurus was not a dinosaur, but a squamate reptile more closely related to today's lizards and snakes. Its shape is unforgettable — a long body, four flippers and a powerful tail.

Its body

The body of Mosasaurus was streamlined, well suited to moving quickly through the sea. Its limbs evolved into four flippers used for steering, while the powerful tail was the main structure that pushed it forward. Some close relatives preserved with soft tissue support the idea that the tail ended in an asymmetrical, two-lobed outline — rather like a natural upturned tail fin.

Its long jaws carried strong teeth for catching and holding fish and other marine animals, and the position of its nostrils and eyes was well suited to watching the water surface from below.

Where it lived and what it ate

Mosasaurus was an apex predator, feeding on fish, cephalopods and other marine reptiles. It lived in warm seas during the Late Cretaceous (about 82 to 66 million years ago). It was known for ambushing prey and bursts of speed, sitting at the top of the marine food chain of its time.

Where its fossils were found

Mosasaurus fossils have been discovered in Europe, North America and other Late Cretaceous seas. One of the most famous early finds came from Europe, and later specimens of the group have been found worldwide, giving scientists a fairly clear picture of its body plan and swimming.

What the fossils tell us — and what they do not

The skeleton reveals its size, the structure of the flippers and its powerful tail, but the colour of its skin, the soft edge of the flippers and the exact shape of the two-lobed tail rely on soft-tissue finds and reconstruction. So the colours and pose you see are evidence-informed presentations.

A note for grown-ups

You could look with a child at where the power comes from: Mosasaurus moved quickly mainly by its tail, not its flippers. Helping a child tell apart "steering" from "powering" is a good lesson in how animals move.