Fossilised remains of a 250-million-year-old animal are leading to a new understanding of how reptiles evolved in the wake of Earth’s largest mass extinction.
A chunky, 1.5-metre-long armoured predator that lived some 250 million years ago may upend our understanding of reptile evolution.
 |
| Prosaurosphargis yingzishanensis – an ancient predator that is helping us understand reptile evolution Andrzej S Wolniewicz, Yuefeng Shen, Qiang Li, et al. |
Fossils of the novel species – named Prosaurosphargis yingzishanensis, because it was found in the Yingzishan quarry in Hubei province, China – were unearthed in 2019. The rocks in which the fossils were found indicate that the animal lived in salty lagoons. It was one of the larger marine reptiles on Earth at the time, says Andrzej Wolniewicz at the Hefei University of Technology, who led the analysis of the remains.
He says that it probably snacked on juicy marine invertebrates and small fishes. But it was also well-protected from other predators: Its body was covered in bony scales and plates, like today’s crocodiles. Wolniewicz thinks the bony armour may have acted as ballast that allowed P. yingzishanensis to walk on shallow seabeds and forage for food.
Wolniewicz and his colleagues concluded that P. yingzishanensis was a saurosphargid, an extinct family of stocky reptiles that were a little like marine iguanas, if marine iguanas were carnivorous and spent more time in water. But its unusual body plan is also similar to that of another group of ancient reptiles – the sauropterygians, which includes the long-necked plesiosaurs that swam the seas during the age of dinosaurs.
This might warrant a whole rethink of how these ancient marine reptiles are classified, says Wolniewicz. He and his colleagues suggest we start thinking of saurosphargids as a sub-group of the sauropterygians. “They were actually, you know, one of the early stages of evolution of the group that eventually led to plesiosaurs,” he says.
This relationship hadn’t been clear before in part because marine reptiles evolved so rapidly 250 million years ago, during the early Triassic. A few million years earlier, the devastating end-Permian mass extinction killed off 95 per cent of all animal species, leaving both the land and the ocean largely empty. The survivors took advantage of the opportunity afforded by that empty ecospace, says Mike Benton at the University of Bristol, UK. He says there was an “astonishingly fast rate of diversification of marine reptiles, where five or six extremely different groups arose and diversified fast”. The discovery of P. yingzishanensis “helps sort out relationships” between them, he adds.
The find has implications for living reptiles, too. For instance, it hasn’t been clear from fossil analysis exactly how turtles relate to other reptiles. But the evidence from P. yingzishanensis helps to place them in a large group that includes reptiles and also birds – a relationship that scientists have suggested before based on DNA analysis, rather than fossils.
“This is a very important step into establishing a consensus on reptile evolution,” says Wolniewicz. “But there is something maybe about these reptiles that we still don’t understand: What actually allowed them to evolve a huge variety of morphologies, as they adapted to life in the water, on land, and in the air even?”
Journal reference:
eLifeDOI: 10.7554/eLife.83163