A New Species Of Freshwater Mosasaur

For over 200 million years, the oceans were ruled by the fish. Sharks cruised the open water, while armoured giants lay in wait around the rocks and reefs on the sea bed. Yet all this changed when the first marine reptiles evolved. At first they were a minority, but quickly they established their dominance over the oceans, becoming some of the biggest and most ferocious predators in Earth history.

The fossil hunter Mary Anning

An artist's impression of the 84 million year
old mosasaur Pannoniasaurus inexpectus

found a lost world of long-necked plesiosaurs, dolphin-like ichthyosaurs and vicious pliosaurs. To swim in the waters of the Jurassic or Cretaceous would be to risk life, but recently discovered fossils has shown that the empire of these marine predators extended further than was first thought.

Today, rivers such as the Nile and the Amazon are home to countless crocodiles and alligators, but hundreds of millions of years ago they were patrolled by relatives of the marine reptiles.

In 1999, several fossils from giant, crocodile-like creatures known as mosasaurs, were unearthed in an open pit mine in Bakony Hills, western Hungary. The 84 million year old specimens belonged to a range of individuals from small juveniles to 20 foot adults. What makes them interesting is that they were found in floodplain sediments, showing that they most likely lived in rivers and lakes, making them the first known freshwater mosasaurs, a group which was once thought to be exclusively marine.

The creatures had a flattened, crocodile-like skull, limbs which may have been capable of supporting their weight on land, as well as acting as a means of propulsion in the water, alongside a long, fluke tail.  These distinctive features meant that researchers classified them as a new species, named Pannoniasaurus inexpectus after the Pannonia region of Hungary as well as their unexpected occurrence in alluvial, rather than marine, sediments.

A diagram showing the fossilised elements of the skull

Their habitat was a floodplain inhabited by a vast range of other water dwellers. Fossils associated with turtles, crocodiles and fish have been found in the same region, together with pterosaurs and a small number of birds. The diversity of potential prey meant that Pannoniasaurus would have thrived. Their size certainly made them top predators.

'To the best of our knowledge, the ancestors of mosasaurs and of some related reptiles moved from land to aquatic realms at least 100 million years ago. Whether these were marine or freshwater environments, is uncertain. However some finds in Japan suggests the latter,' said László Makádi, a palaeontologist from the Hungarian Natural History Museum.

The researchers hope to find more fossils of Pannoniasaurus to find out about its physiology and lifestyle. The evolutionary history of marine reptiles is diverse and fascinating, but this discovery shows that there are potentially many more species that we do not yet know about.