New Fossil Evidence Provides Insight Into The Aquatic Adaptations Of Mosasaurs

A complete fossil of Ectenosaurus (top) and
the recent fossils of soft tissues (bottom)

Mosasaurs were some of the largest aquatic reptiles on Earth. These predatory reptiles dominated the seas for nearly 100 million years. They grew to vast sizes, some topping 15 metres. We know what they ate, how they bred, even how they gave birth, yet little about how they swam. Early reconstructions of the Mosasaur suggested they held their body rigid, moving their fins in a fashion similar to oars.

More recent versions suggest that it rippled its body up and down, having the dual effect of reducing drag. The fins were simply a means of directional control, and secondarily, propulsion. Now a team of scientists, led by Dr Johan Lindgren from the Lund University in Sweden, believe that they have found a new model for the way Mosasaurs swam and used hydrodynamics. Their evidence is based around a late Cretaceous Mosasaur called Ectenosaurus.

The first fossils of Ectenosaurus were recovered in 1864. More were discovered in 1967 in the phosphate beds of South West Kansas. This was fortunate as phosphate fossils are some of the most well preserved that can be found. These fossils displayed soft tissue and scales. This allowed the team to make incredibly accurate reconstructions of the creatures and then place them in environments which obey the laws of physics such as drag, gravity and propulsion.

They found that the scales would have greatly reduced the water resistance, especially at the torso. They also believe that the Mosasaur would have held the front of its body rigid, while the fins and abdomen provided propulsion. Dr Lindgren described these new findings as  'unique insights into the biology of an extinct group of marine lizards that became adapted to aquatic environments in a fashion similar to that of the preceding ichthyosaurs ('fish-lizards') and succeeding whales.' This study will be an invaluable stepping stone in future investigations into how reptiles adapted to life in the seas.