This 242-million-year-old creature swam the seas before most dinosaurs roamed the planet. It’s the oldest known marine reptile to feast exclusively on plants. And its mouth is full of mysteries.

Its name, Atopodentatus unicus, which is Latin for “unique strangely toothed,” provides a clue to its puzzled past. Paleontologists in China first found its fossils in 2014, and believed it had a jaw shaped like a flamingo’s beak with a zipper of teeth down the middle.

But those assumptions were wrong, according to a new paper published Friday in the journal Science Advances. Rather than a downward-turned snout, the reptile actually had a flat hammerhead-shaped face, the paper says.