True ‘river monster’ fossils discovered by team with Alberta paleontologist

Pannoniasaurus reconstruction. LiveScience.com photoDigging through the layers of a bauxite mine in Hungary, an international team of paleontologists has uncovered fossilized remains of several mosasaurs. The remains of  the massive lizards that lived in the Cretaceous Period have revealed some surprising new details about the evolution of the species, the team reports.

Mosasaurs weren't dinosaurs, but a species of true lizards — cold-blooded and able to dislocate their jaw to swallow anything that would fit inside their mouth. They were one of the largest predators in the ancient oceans — air-breathing, growing up to 16 metres in length, with paddle-like fins (similar to a whale's) and a gaping jaw filled with razor-sharp teeth that could unhinge to swallow anything that would fit inside — and their fearsome appearance earned them the nickname "T.Rex of the Sea."

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This new mosasaur, called Pannoniasaurus, shares the same jaw structure as the rest of the species, but is the first example found that lived in freshwater, and also that has legs like a land-dwelling lizard.

"This is kind of new stuff for us in the mosasaur world," said Michael Caldwell, a paleontologist from the University of Alberta, who was a member of the team and co-author of the study published on Wednesday. "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. Mosasaurness is really about the skull and about habits, as opposed to everything but the head being focused on swimming adaptations."

"It's an elegant and exciting example of evolution at work," he said. "If the ancestors of all mosasaurs started out on land, the existence of Pannoniasaurus shows that the move from land to ocean took place at different times and in different ways, depending on what evolutionary pressures were at work. They’re going through the high end of aquatic adaptations at different times and under different selection pressures."

The found remains come from several different animals of various ages and sizes. This shows that this isn't just an isolated case, but a true subspecies of mosasaur.

"This is really exciting new news in the business of evolutionary biology. It's almost like saying hominids evolved more than once, and having the fossil evidence to say so."

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