Chinese fossil of hammerhead marine reptile so weird its finders were ‘blown away’

Crocodile-sized plant eater dug up in Yunnan used its chisel-shaped teeth to scrape algae off rocks, scientists figure out after making model of its jaw using children’s clay and toothpicks

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A fossil of the herbivorous marine reptile Atopodenatus unicus alongside a reconstruction showing what it would have looked like in life. Photo: Nick Fraser

Published: 2:01am, 7 May 2016Updated: 2:01am, 7 May 2016

Two years ago, scientists in Yunnan province in southwest China found a peculiar-looking, beautifully preserved, 242-million-year-old marine reptile the size of a crocodile with a mouth like a zipper.

Science writer Brian Switek wrote in National Geographic magazine that its cranium looked like “a bony version of a Scotch tape dispenser” and that it was so strange it made him “jolt upright in my seat and think ‘Wait, what the hell is that?’”

Nicholas Fraser, keeper of natural sciences at National Museums Scotland, says that he, along with Professor Li Chun, of the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, and Olivier Rieppel, a curator at the Field Museum in Chicago, puzzled over two newer specimens for 10 to 14 days before they had a breakthrough.

“We were blown away by how weird it was. We weren’t expecting to see anything like this … Although it’s well articulated, it’s still compressed a bit,” Fraser says. “So we went and bought some children’s clay…and we bought some toothpicks.”

To figure out how the animal's jaw worked, the scientists turned to children's clay and toothpicks. Photo: Olivier Rieppel/The Field Museum

That was the only way they could think of to figure out how the animal’s jaw worked. They realised that, unlike almost all other marine reptiles, this one, called Atopodentatus unicus, ate plants, making it the oldest herbivorous marine reptile in the fossil record. The only plant-eating marine reptiles alive today are green sea turtles and marine iguanas.