Bizarre Hammerhead Was the First Vegetarian Reptile in the Ocean

May 9, 2016 | Erica Tennenhouse

A fossil of Atopodenatus unicus is alongside a reconstruction showing what it would have looked like in life.
Photo credit: © Nick Fraser

It arose in the wake of the world’s largest mass extinction

242 million years ago, in what is now southern China, lived a sea-dwelling reptile with a bizarre feature — a hammerhead-shaped jaw. The unusual shape helped the reptile eat plants from the ocean floor. It is the earliest known example of marine reptile to dine exclusively on plants.

"It’s a very strange animal,” said Olivier Rieppel, a curator at The Field Museum in Chicago and co-author of a recent paper describing a fossil that was discovered in 2014, in a press release. “It’s got a hammerhead, which is unique, it’s the first time we’ve seen a reptile like this.”

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The reptile, called Atopodentatus unicus — Latin for “unique strangely toothed” — certainly lived up to its name. Scientists found its wide jaw contained rows of peg-like teeth along the edge, and then bunches of needle-like teeth further into its mouth.

“It used the peg-like front teeth to scrape plants off of rocks on the seafloor, and then it opened its mouth and sucked in the bits of plant material,” explained Rieppel. “Then, it used its needle-like teeth as a sieve, trapping the plants and letting the water back out, like how whales filter-feed with their baleen.”

The structure of the jaw was clearly consistent with an herbivorous diet. Other marine reptiles were known to eat plants with a similar filter-feeding system, but the hammerhead is roughly eight million years older than them.

The hammerhead arrived a mere ten million years after the Permian-Triassic extinction, which was the world’s largest mass extinction event that wiped out about 95 percent of all marine life. “The existence of specialized animals like Atopodentatus unicus shows us that life recovered and diversified more quickly than previously thought,” said Rieppel.

Strange creatures are known to have crept up in the wake of the massive extinction, and the hammerhead is just about as strange as any of them. Rieppel remarked, “It’s definitely a reptile that no one would have thought to exist—look at it, it’s crazy!”

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