A new study has raised the possibility that ancestors of the predator dinosaur may have been vegetarian.
Lindsay Zanno and colleague Peter Makovicky collected data for theropods, commonly called "predatory" dinosaurs, a group that also includes Tyrannosaurs rex.
"Carnivory is always rare relative to herbivory in animal communities because food availability becomes more scarce as you move up the food chain," Discovery News quoted Zanno as saying.
"It takes a ton of plant material to sustain a lot of herbivores and a lot of herbivores to sustain a few carnivores."
Talking about the evolution of beak in dinosaurs, Zanno said, "As modern animals such as birds and turtles demonstrate, a beak can be adapted to function for a variety of purposes from processing different food types -- nuts, fruits, leaves and meat -- to grooming and other behaviors."herefore, the team concluded that many of T. rex's closest relatives could have been vegetarians.
Zanno explained that important traits associated with herbivory are tooth loss, beaks, different tooth shapes (leaf, peg conical), multiple tooth types in one animal, tooth elongation (including rodent-like incisors), and long necks.
The researchers looked at evidence that included fossilized dinosaur dung, stomach contents, tooth marks, gastric stones and even two dinosaurs locked in the throes of combat.
They found nearly two-dozen anatomical features that are linked to plant-based diets. The researchers believe beaks evolved at least five times in theropods alone. Other dinosaurs, like ceratopsians and hadrosaurs, had them too.
"The ancestors to birds had teeth as did many early birds, so none of the toothless forms are directly ancestral to birds," Zanno explained.
They concluded that, "the ancestor to birds was likely to be at least omnivorous."
The study is published in the latest Proceedings of the National Academy of Sciences.