Mosasaurs were large marine reptiles. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from semi-aquatic squamates known as aigialosaurs, which were more similar in appearance to modern-day moniter lizards, in the Early Cretaceous.
When it came to be the last 20 million years of the Cretaceous, which brought the extinction of a few other marine predators, the Mosasaur became the dominant marine species.
The Mosasaur was able to breath air, was a powerful swimmer, and were easily able to adapt to warm, shallow seas.
Mosasaurs had a double-hinged jaw and a flexible skull, making them somewhat similar to modern day snakes. This helped them to easily gulp down their prey nearly whole.
Size: The Mosasaur was typically about 3.0 metres (9.8 ft) to 3.5 metres (11 ft) long at its shortest. At its largest, around 17.5 metres (57 ft).