Tracks found in Yunnan, China, suggest a method of travel and foraging for nothosaurs, marine predators that wandered the coasts 245 million years ago.

These hunters, consisting of the small Lariosaurus and its impressively sized cousin, the Nothosaurus, were the top of the seafloor food chain back in their day.

The discovery is helping scientists understand exactly how these predators roamed the seas and captured their prey. With long bodies and flat limbs, nothosaurs could have traveled with paddle-like motions, rowing through the water and searching for their victims. Perhaps they swam by waving their limbs in circular motions, similar to the way penguins swim. Until now, there was no evidence to help scientists answer this question. 

The tracks found were long, paired slots in straight lines and curves, likely created by the forelimbs of the nothosaurs. The motion indicated by these tracks suggests that nothosaurs used unison sweeping motions to get from one point to another, but the purpose was not simply transit. Scientists conducting the research, both at University of Bristol and the Chengdu Center of China Geological Survey, believe the sweeping motions were also foraging mechanisms. The nothosaurs' forelimbs disturbed the smaller fish and other organisms inhabiting the mud at the bottom of the sea, churning them up as easy lunch.

A press release by the University of Bristol explains how difficult it is to find such well-preserved evidence of marine reptile locomotion. Qi-yue Zhang of the Chengdu Center happened across the tracks (350 prints total) while mapping some unique features of the Yunnan province. While this area is famous for fossils, the preservation of the nothosaur tracks was more exquisite than the scientists could have hoped.

Not only was this evidence much sought-after, but it also gives a glimpse into the resilience of life after massive destruction. At the start of the Mesozoic Era and the end of the Paleozoic, 252 million years ago, a mass extinction event destroyed more than 90 percent of life. Some 90 percent of marine species and 70 percent of terrestrial species went extinct, yet 8 million years later, ravenous reptiles were digging up the seafloor for their victims.

"It took all that time for the Earth to settle down from the cataclysm, and the arrival of these large, complex marine predators shows us the ecosystems had finally rebuilt themselves, and life could be said to have recovered from the crisis," says Professor Shixue Hu, co-author of the research, which was published in Nature Communications on June 11.

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