Paddle Prints bring Swimming Techniques of Ancient Reptiles to the Surface

Scientists are quite literally following the tracks of ancient marine reptiles, whose paddle prints shed light on how they propelled themselves through water.

Nothosaurs, ancient marine reptiles swimming the seas 252 to 66 million years ago during the dino era, are a mysterious creature. These voracious semi-aquatic hunters had elongated bodies and paddle-like limbs, and were among the top marine predators around along the Triassic coasts.

But how they ruled and paddled the seas has been long debated. Scientists have several theories, suggesting that they either rowed themselves along with a back-and-forth motion of their limbs, or "flied" underwater penguin-style, sweeping their forepaddles in a figure-eight motion.

Lucky for them, scientists recently discovered tracks in an ancient seabed in Yunnan, southwest China - likely made from the large Nothosaurus and the diminutive Lariosaurus, two types of nothosaurs.

A series of ten to fifty tracks were found in the mud, consisting of slots arranged in pairs, followed by straight lines and sweeping curves. The size and spacing of the paired markings point to nothosaurs, which ranged in size from over 3 meters to less than a meter in length.

The tracks are not only the first direct evidence that these reptiles propelled over the seafloor by rowing their forelimbs in unison, but also sheds light on how these predators scavenged for food.

"We interpret the tracks as foraging trails. The nothosaur was a predator, and this was a smart way to feed," Professor Qiyue Zhang, leader of the China research team, said in a statement. "As its paddles scooped out the soft mud, they probably disturbed fishes and shrimps, which it snapped up with needle-sharp teeth."

The region around Luoping in Yunnan is a well-known site of exceptional fossil preservation that has yielded thousands of exquisite fossils of sea creatures, though scientists could not predict they would discover tracks in such pristine condition.

"When I first saw the site, I couldn't believe the amazing quality of the fossils. It's quite unusual to find skeletons of marine reptiles such as the nothosaurs so close to evidence of their tracks," commented co-author Michael Benton of the University of Bristol.

The evidence is described by a team from Bristol and China in Nature Communications.