A prehistoric marine reptile sported rows of fearsome razor-sharp teeth resembling chisels and needles. But these scary-looking creatures, roughly the size of modern crocodiles, were herbivores, feasting on grasses and plants.

Atopodentatus unicus sported a snout shaped like a hammerhead, allowing the creatures to graze on plants covering the ocean floor.

This hammerhead creature is the world's oldest-known marine herbivore, more than 8 million years older than the previously oldest-known underwater plant eater. The species lived roughly 242 million years ago, during the middle Triassic period, at the height of the age of dinosaurs. Remains of the first of these ancient reptiles was found in southern China. However, the condition of this fossil was so bad that paleontologists believed the animal possessed a beak like a flamingo.

Atopodentatus unicus translates as "unique strangely toothed," in note of its bizarre dental anatomy. The species possesses a single row of chisel-like upper teeth together with two rows tracing the bottom of the mouth. Other areas along the jaw were covered in needle-like teeth.

The larger teeth likely served the purposes of raking grasses and trimming the edible plants. The animal likely took water into its mouth to strain the vegetation between a mesh created by the needle-like structures.

"It's a very strange animal. It's got a hammerhead, which is unique, it's the first time we've seen a reptile like this," Olivier Rieppel, from the Field Museum in Chicago, said.

In order to get a better understanding of how the jaw fit together, researchers created a model of the structure from children's modeling clay and toothpicks. It was through the modeling that they saw how the creatures fed, in a manner similar to the way some whales currently utilize baleen to strain their food. A similar method of straining vegetation was also used by the next oldest-known marine herbivore.

This study also reveals life recovered and diversified, following the world's greatest extinction event, 252 million years ago, much faster than believed.

Marine mammals are rarely herbivores. One of the few modern examples is the marine iguana living in the Galapagos Islands, a species that eats algae off rocks.

Discovery of the newly-recognized species of marine herbivore was profiled in the journal Science Advances.