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Mosasaur Fossils Are Of The First Freshwater Mosasaur Species

December 20, 2012
Image Caption: Holotype of Pannoniasaurus inexpectatus. Quadrate (MTM 2011.43.1.) in lateral (A), anterior (B), medial (C), posterior (D), dorsal (E) and ventral (F) views. Scale bar represents 1 cm. (doi:10.1371/journal.pone.0051781.g003)

Brett Smith for redOrbit.com – Your Universe Online

Hungarian paleontologists have discovered evidence of a new freshwater-dwelling species of mosasaur, an ancient lizard that thrived during the Late Cretaceous period, about 84 million years ago.

According to the research team´s report in the open-access journal PLOS ONE, the new species of mosasaur, dubbed Pannoniasaurus, grew up to 20 feet in length and had some of the physical characteristics of both crocodiles and whales.

The creature inhabited the ancient waterways that once crisscrossed the Hungarian landscape on their way to the sea, researchers said. Previous studies have suggested that the site was part of a chain of tropical islands located in a freshwater “seaway,” which sat between Africa and southern Europe.

“The evidence we provide here makes it clear that similar to some lineages of cetaceans, mosasaurs quickly adapted to a variety of aquatic environments, with some groups re-invading available niches in freshwater habitats,” said report co-author Laszlo Makadi from the Hungarian Natural History Museum. “The size of Pannoniasaurus makes it the largest known predator in the waters of this paleo-environment.”

The fossils were recovered from a waste dump of a coal mining operation in the Bakony Hills of Western Hungary. The researchers were able to find thousands of fossils from several individuals, ranging in size from 3 to 13 feet. The smaller fossils most likely belonged to juvenile mosasaurs, scientists said.

“What’s really cool is we have a place where they were living, and living at all stages in their life cycle,” co-author Michael Caldwell, a mosasaur expert from the University of Alberta in Canada, told National Geographic.

“Finding young or even smaller-bodied versions is as rare as hen’s teeth in the fossil record of mosasaurs,” he added.

Other fossils recovered at the site showed that these freshwater rivers were also inhabited by fish, amphibians, turtles, lizards, crocodiles, and dinosaurs. The researchers speculated that the Pannoniasaurus was at the top of the ecosystem´s food chain; however, its small, sharp teeth imply that it fed mostly on fish, amphibians and smaller lizards.

“I doubt it was a gigantic predator,” Caldwell told National Geographic reporter Ker Than. “It was probably just catching fish and perfectly happy doing that.”

While the paleontologists stopped short of saying that Pannoniasaurus was restricted to freshwater environments, they said the fossil evidence they recovered highly suggested that possibility.

Caldwell added that mosasaurs probably weren´t the only ancient marine reptiles to successfully adapt to a freshwater environment.

“I’m sure there were freshwater plesiosaurs and freshwater ichthyosaurs,” he told Than, referring to other prehistoric marine reptiles. “We just don’t have the evidence yet.”

In the report, the researchers noted that this is the first mosasaur that lived in freshwater, and only the second fossil specimen of a mosasaur found in rocks that were not once located in the ocean. Fossils of the mosasaur Plioplatecarpus were recovered from freshwater sediments in Canada, but the lack of related finds suggests a random occurrence with no ecological implications. Another mosasaur species, Goronyosaurus, has been suggested as a candidate for freshwater adaptiveness based on its skull morphology.


Source: Brett Smith for redOrbit.com - Your Universe Online



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