A Tiny Swimming Hunter From the Jurassic Helps Explain How Mammals Evolved

Scientists have studied the fossil of a furry hunter that lived 165 million years ago, and it is teaching them about how mammals developed. The animal is called Megacauda sungei. It was only about half a meter (20 inches) long from nose to tail, yet it was large next to most of its Jurassic relatives. It was a water hunter, and its backward-curved teeth helped it grip slippery prey.

With its short fur and wide, flat tail, it would have looked a bit like an otter, a beaver or a platypus. Scientists scanned the fossil with computed tomography, a type of 3D X-ray, to build detailed models. They suggest that it swam by paddling with its front legs and waving its tail, using its back legs to steer.

The most important discovery, though, was inside its mouth. The researchers found signs of a soft palate, the soft part of the roof of the mouth, which separates the mouth from the pharynx, the passage that connects the mouth to the throat. A soft palate makes it possible to swallow and still breathe. That matters for mammals that nurse their young with milk. The study was done by researchers in Shenyang, Chicago and Bonn and published in the journal Nature.

Many animals do not have a soft palate and use a simpler arrangement of hyoid bones in the throat. Crocodiles, for example, lift their heads and jerk them to move food down, using gravity to help, explains paleontologist Thomas Martin of the University of Bonn. Mammals have a more complicated hyoid structure that lets them swallow even against gravity. Humans can drink through a straw while upside down and still breathe.

This ability lets baby mammals drink milk without it going up into their noses. Martin says that this adaptation made brain development possible, a path that eventually led to humans. Megacauda sungei already showed signs of it millions of years before modern mammals appeared.