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

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

Alan Yu

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.

Fraser says the reptile has a hammerhead jaw with chisel-shaped teeth at the end. It would have scraped algae and similar plants off rocks in the sea, gulped them down along with water, and then used a sieve-like arrangement in its teeth to force the water out.

An artist’s impression of what the reptile would have looked like. Image: Yu Chen
The researchers say there could be more discoveries like this from the same part of China, and that their find shows life adapted more quickly than had been thought after one of Earth’s mass extinction events wiped out most life on the planet. Their analysis is published in the journal Science Advances.
As much as 95 per cent of all life in the sea, and 70 per cent of life on land, became extinct at the end of the Permian period in what has been called “ the Great Dying.” All life on Earth today is descended from what survived.

Fraser says: “The skull is pretty small, 10 to 12 cm … so this is a feeding machine, it’s grabbing the algae material, and it’s swallowing it, and it’s processing it down in the stomach and into the intestine, it is not doing any processing of the food in the mouth.”

Michael Pittman, a vertebrate palaeontologist and research assistant professor at the University of Hong Kong, calls it an “amazing fossil”.

He says the researchers could further prove the reptile ate plants by looking for algae preserved in gut specimens, studying how the teeth were worn down under an electron microscope, or studying the chemical make-up of the teeth (animals that eat plants have slightly different teeth from those that prey on other animals).

An artist's drawing of the marine reptile shows it scraping marine plants from the sea, sucking them in and filtering out the water. Image: Yu Chen

Fraser says scientists used to think it would have taken a long time for life to recover from a mass extinction, but this discovery adds to a growing body of evidence that there were many diverse forms of life around within six to eight million years after that mass extinction.

“That is not long in geological time, and certainly (in) evolutionary terms, this is actually a fairly short period,” he says. “This is just one more piece of evidence to indicate that life recovered relatively quickly.”

There could be more discoveries in Luoping county in Yunnan. In 2010, the Guardian reported that 20,000 fossils, forming a 252-million-year-old marine ecosystem, were found there. Li Chun, of the Institute of Vertebrate Palaeontology and Palaeoanthropology and the lead author of the paper on this fossil, says: “This is a locality with the most abundant marine reptile fossils in the world … maybe, just maybe the oldest turtle/crocodile/pterosaur would be found here someday.”
An artist's restoration of the animal's head, which one science writer described as “a bony version of a Scotch tape dispenser”. Image: Wang Yu
Fraser shares Li’s view. He explains that 240 to 245 million years ago, Guizhou and Yunnan were at the edge of a massive sea called Tethys that stretched from there to what is now Switzerland and Italy. He says this region has yielded some “fantastically preserved fossils” unlike those found elsewhere in the world. He says his team is working on other specimens, and says discoveries made in Yunnan could potentially be as revolutionary as the discovery of feathered dinosaur fossils in Liaoning, in northeast China, which helped scientists understand the origin of feathers, flight, and the evolution of birds.

“We’re just starting to enter this period of research, so it’s exciting times.”

Four other weird fossils found in China

1. In 2014, researchers founded a 520-million-year-old, balloon-shaped animal with an outer skeleton of defensive spikes. It looks like a “squashed bird’s nest”.
2. In February 2016 researchers found a half-billion-year-old fossilised nervous system from a crustacean-like-animal, so well preserved that the individual nerves are visible. It could help us understand how early animals developed a nervous system.
3. In April 2015, Chinese scientists found the first dinosaur to have “hybrid” wings with feathers and a membrane like that of bats. The 160-million-year-old fossil, named yi qi, which means “odd wings” could change our understanding of how dinosaurs evolved into birds.
4. In June 2015, scientists found a half-billion-year-old “ super-armoured worm” that filters nutrients out of the water using feather-like legs. It’s one of the first animals on earth to develop armour.