Mosasaur discovery a true ‘sea monster’

It grew up to six metres long and its toothy mouth and crocodile-like body was the terror of ancient rivers many millions of years ago. Just don’t call it a dinosaur. “Mosasaurs are not dinosaurs,” said University of Alberta biologist Michael Caldwell, who discovered a new type of the long-extinct marine lizard in a bauxite mine in Hungary.

Mosasaurs, unlike dinosaurs, were true lizards, meaning they were able to dislocate their jaw at will and swallow anything they could get their mouths around. This is what makes Caldwell’s mosasaur — called Pannoniasaurus — so interesting.

Most mosasaurs were giant undersea predators, some up to 16 metres long, which breathed air but were full-time, fearsome sea creatures complete with paddle-like limbs similar to those of a whale. They lived around the same time as dinosaurs and have been called the T. rex of the sea.

“They were much bigger than T. rex,” said Caldwell, a mosasaur expert. “They really were sea monsters.”

Pannoniasaurus, however, wasn’t. About 84 million years old, it is the first mosasaur found that lived in freshwater and retained the long, skinny legs of a land-based lizard. Judging by the shape of its skull and the abundance and type of its teeth, it probably hunted much like a crocodile, lurking just under the surface of the water to suddenly pounce on fish, or frog, or anything that moved.

But even though Pannoniasaurus didn’t have the marine lifestyle or the seal-like flippers, it still shared one essential characteristic — the bone at the back of its skull that allowed its jaws to gape so impressively.

“Up until about five to 10 years ago, we treated the group as though it had a common ancestor with paddle-like limbs. We’re beginning to recognize that the story is remarkably more complex than that,” Caldwell said.