Usually animals that use stomach stones tend not to need tough beaks. For instance, chickens have puny beaks, relying on sand and gravel in their gizzards to grind down their unchewed food.
Sereno's "very compelling argument that the [new dinosaurs] were eating unusually hard food makes good sense to me," Sues said.
Odd And Successful
Several species of psittacosaurs roamed Central Asia, where their fossils are now plentiful, scientists say.
The creatures often had odd features, such as elaborate horns and porcupine-like tail bristles. (See other photos of bizarre dinosaurs.)
Study leader Sereno said that the psittacosaurs' specialized diet might explain their success during that time.
That's because animals that take advantage of their environments—in this case, eating what few other animals could—have plentiful resources and are therefore more likely to branch into more species, added Sues of the natural history museum.
The new research, he said, "offers a very nice explanation about why these creatures are so diverse."
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