Some dinosaurs were picky eaters. Certain plant-munching dinosaurs preferred specific parts of plants, new data show.  

Researchers have long thought that what these herbivorous dinos ate was based on their height. But a new study challenges that. Chemical clues in 150-million-year-old teeth suggest they instead selected food based on its nutrients and texture.

“Herbivores had different diets,” says paleontologist Liam Norris. He works at the Texas Science & Natural History Museum in Austin. “If they are eating softer parts like leaves, versus eating twigs or maybe bark, that looks like it is more significant” than a species’ size.

His team studied dinosaur tooth enamel. This is the hard outer material on teeth. The researchers focused on its calcium isotopes. (These are forms of an element that have different numbers of neutrons.) Certain isotopes correspond to what the dinos had eaten. A wider range of calcium-isotope levels points to a more varied diet. 

Norris and his group figured out a plant eater’s favorite foods by comparing the dinos’ tooth-isotope levels to those of modern herbivores.

The towering Camarasaurus lived in the Late Jurassic period. That was between some 164 million to 145 million years ago. Researchers had thought this long-necked dino mostly ate leaves from treetops. It certainly could have reached these somewhat soft bits. But it ate rougher stuff — woody plants and twigs, the study now concludes.

Meanwhile, the smaller, beaked Camptosaurus preferred softer plant parts, such as leaves and buds. These and other herbivores might have been able to coexist because they ate different foods.

Calcium clues

“People have been looking at dinosaur teeth for many decades,” says dinosaur expert Paul Barrett. He didn’t take part in the new study but works at the Natural History Museum in London, England. “This is a nice, new method for looking at the same kind of problem,” he says. Calcium isotopes, he adds, could help where few data exist on a dino’s diet.

Norris’ team also measured calcium-isotope levels in the teeth of two carnivores, or meat-eaters. The data suggest the crocodile-like Eutretauranosuchus ate mostly fish. The fierce Allosaurus, in contrast, dined mostly on the flesh of other dinosaurs. But Allosaurus didn’t munch much on bones, as Tyrannosaurus rex did. Both T. rex and Allosaurus are theropods that stood on two legs.

Norris’ team shared its findings in the Oct. 1 Palaeogeography, Palaeoclimatology, Palaeoecology.

Researchers had long looked at calcium isotopes in tooth enamel for hints at what some animal ate. But this is one of the first times the technique has been used on very old dinosaur teeth, says Michael Benton. A paleontologist, he works at the University of Bristol in England.

“I think this is an innovative method,” he says of the new work. It’s difficult to do it well, he adds. But it confirms that chemical signs of diet stick around for a very long time.