Presumed Vegetarians Also Ate Meat

Until now, paleontologists have generally assumed that hadrosaurs and other large herbivorous dinosaurs were strict plant-eaters, like modern-day elephants and rhinos, said Chin. But the crustaceans in their waste demonstrate that at least some of them were ingesting meat, and Chin doubts they were doing so completely by accident. The crustaceans in the coprolites would have been about 2 inches long, big enough for a 30-foot-long hadrosaur to spit out if it accidentally scooped one up with a mouthful of rotten wood.

"When you find evidence like this, it does require that you sort of expand your ideas about how things as large as ceratopsians and hadrosaurs may have obtained enough nutrition," said Roberts. "It opens up the way that I think about dinosaur ecology."