News
9 May 2016

Prehistoric hammerhead was first herbivorous marine reptile

The croc-sized reptile wasn't a ferocious predator – it preferred a vegetarian menu, scientists claim. Amy Middleton reports.

A fossil of Atopodenatus unicus alongside a reconstruction.Credit: Nick Fraser

A crocodile-sized, prehistoric, hammerhead reptile doesn’t sound like something you’d want to meet in the sea, but a new study suggests this creature was actually a herbivore – its unique teeth evolved for picking up plants off the ocean floor.

Fossils of the playfully named Atopodentatus unicus, Latin for “unique and strangely toothed”, was discovered in 2014 by researchers in southern China. 

Analysis dated the marine creature at around 242 million years old, but the fossil had severe damage to its head, keeping its unique teeth and jaw shrouded in secrecy. 

A new study by an international team suggests that a T-shape adorned the head of the marine creature, which was probably used to forage for underwater foliage, rather than prey. This research places the sea-dweller as the earliest known marine herbivore.

“It's a very strange animal," says Olivier Rieppel, a biologist at the Field Museum in Chicago and co-author of the study. "It's got a hammerhead, which is unique. It's the first time we've seen a reptile like this." 

To figure out the head and jaw structure of the herbivore, researchers used tools one might associate more closely with school projects: clay and toothpicks.

“To figure out how the jaw fit together and how the animal actually fed, we bought some children's clay, kind of like Play-Doh, and rebuilt it with toothpicks to represent the teeth," explains Rieppel. 

"We looked at how the upper and lower jaw locked together, and that's how we proceeded and described it."

Initially, researchers claimed the reptile sported a flamingo-like beak, which it used to stir up invertebrates in sea-floor sediment. But this paper describes the creature’s upper and lower jaws as being laterally squared-off in opposite directions, with chisel-like front teeth and a mesh of tightly packed, needle-shaped teeth towards the back of its mouth.

This system was ideal for collecting foliage off the sea-floor, Rieppel explains. "It used the peg-like front teeth to scrape plants off of rocks on the sea floor, and then it opened its mouth and sucked in the bits of plant material.

"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.”

Herbivores in the marine reptile world are scarce, and this is the oldest example on record. "The jaw structure is clearly that of a herbivore," says Rieppel. "It has similarities to other marine animals that ate plants with a filter-feeding system, but Atopodentatus is older than them by about eight million years."

The paper points to a number of other hammerhead-shaped skulls among vertebrates with different biological functions.

For example, the hammerhead shark, which is alive today, uses the eyes on its T-shaped head to improve its vision.

The work was published in Science Advances.

Amy Middleton is a Melbourne-based journalist.