Mosasaurus conodon

One of the most widespread and numerous marine reptiles of the Cretaceous era. The Mosasaurs exploded into the ecological niches left vacant by the extinction of the Ichthyosaurs at the end of the Jurassic.

Remains of Mosasaurs have been found all over the world from Europe to Australia, Antarctica, and Africa. Huge numbers of them have been unearthed in the American Midwest, which was the ancient bed of the Niobrara sea that cut North America in two during the Cretaceous.

Even though there were other large hunters that shared the sea with the Mosasaurs, such as Pliosaurs, huge sharks and Plesiosaurs, these species never matched them in terms of sheer numbers.

Mosasaurs swam with an undulating side to side motion of the their broad flat tail and maneuvered with large flippers. They are known from fossil evidence to have given live birth to their young, and were often combative with each other and sometimes cannibalistic.

By the end of the Cretaceous some mosasaurs were reaching larger sizes ( 40 to 50 feet ) and others were radiating into more specialized modes of existence, creating many new species. A testament to their success.