A trove of 84-million-year-old fossils recently discovered in western Hungary belongs to what appears to be a family of a new mosasaur species. Mosasaurs are large crocodile-like reptiles from between 66 to 100 million years ago that, until now, scientists believed only lived in marine environments. The fossils belong to a species that paleontologists have named Pannoniasaurus inexpectatus, the first mosasaur species discovered to live in freshwater. The research team, led by Laszlo Makadi, a paleontologist at the Hungarian Natural History Museum, was excited to find not just one organism’s fossil, but a number of Pannoniasaurus specimens representing a range of ages. Finding juvenile specimens’ fossils is unusual in itself, but finding them alongside adults is even rarer, and tells scientists a whole lot about how that species lived. Makadi and colleagues believe that, due to the variety of ages of specimens, these Mosasaurs lived in groups with more than one family unit, and lived their whole lives in freshwater, versus arriving there later in life from a marine environment.
Pannoniasaurus may be the only freshwater mososaur. But another explanation for the lack of freshwater mososaur fossils may be that marine fossils are simply more likely to form than are freshwater ones. When an organisms dies in a marine environment, it falls to the bottom of the ocean, which is covered in sediment that is rich in minerals, which make it easier for mineralization to occur, the process of replacing bone with minerals and subsequently forming a fossil. Freshwater environments have less sedimentary rocks, and fossilization is more difficult there. Also in the sea, wave action causes the organism to be buried faster, so it isn’t open to the water and sun’s rays, and is therefore less susceptible to oxidation and deterioration. (Read more about how fossils are made at chestofbooks.com)
Pannoniasaurus inexpectatus looked like a cross between a large crocodile and a small whale. The specimens ranged from younger guys who were 28 inches long to adults who measured up to 20 feet. They had long tails that were consistently about half the length of their bodies. The tails undulated back and forth, allowing for speedy swimming in the waters between Africa and southern Europe, where the researchers think Pannoniasaurus primarily lived. Pannoniasaurus had small limbs that were probably used to steer and brake itself when swimming. Makadi and fellow study authors think that the limbs may have also allowed Pannoniasaurus to creep along the ground in shallow waters, much as modern-day crocodiles do. P. inexpectatus fossils were found alongside those belonging to fish, amphibians, lizards, and crocodiles, but Pannoniasaurus was by far the largest organism in the area, so scientists think this mosasaur was probably a predator . However, Pannoniasaurus had relatively small, sharp teeth, so these mosasaurs probably didn’t eat very large prey.
Read the study in the journal PLoS One.
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