A crocodile-sized creature that lived 242 million years ago was the first known vegetarian reptile to live in the sea, according to new evidence.
Two fossils found in China show what the animal looked like.
Scientists say its hammer-shaped skull helped it to feed on underwater plants.
Only a handful of marine reptiles, living or extinct, are known to be vegetarian.
Scientists used modelling clay, like Play-Doh, to re-make the jaw to work out how the animal fed. They used toothpicks to represent the teeth.
Olivier Rieppel of the Field Museum in Chicago said:
"We looked at how the upper and lower jaw locked together, and that's how we proceeded and described it."
"It's definitely a reptile that no one would have thought to exist - look at it, it's crazy!"
The first fossils of the creature were discovered a few years ago.
It was named Atopodentatus unicus, which is Latin for "unique strangely toothed".