The 110-million-year-old skull—as well as "a huge pile" of 50 stomach stones found with the fossil—suggests that the beast was chewing hard, fibrous nuts and seeds, the researchers say. Stomach stones are rocks ingested by some animals to grind food in their digestive systems.

If confirmed, Psittacosaurus gobiensis ("parrot reptile of the Gobi") and its close cousins would be the world's first known nut-eating dinosaur.

Knowing what type of food a dinosaur ate is extremely rare, said study leader Paul Sereno, a paleontologist at the University of Chicago.

"Basically this solves a bit of a riddle for this dinosaur," said Sereno, who is also a National Geographic explorer-in-residence. (The National Geographic Society owns National Geographic News.)

"We've now come closer to why it looks like it does."