Lindsay Zanno and Peter Makovicky say in a research paper that most theropods—the family of the T-Rex and the Velociraptor—were actually vegetarians.
According to the two paleontologists at Chicago's Field Museum—who I would put inside a cage along with a pack of living velociraptors—most of the dinosaurs that we believed to be meat eaters were actually plant eaters. In fact, they say hunting therapods like the Velociraptor and the Tyrannosaurus Rex were the exception to this rule.
Their study—Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution, which just appeared in the December 20, 2010 issue of Proceedings of the National Academy of Sciences—has detected "21 morphological features that exhibit statistically significant correlations with extrinsic fossil evidence of coelurosaurian herbivory, such as stomach contents and a gastric mill."
After studying 90 theropod species, their conclusion is that vegetarianism was widespread and "contrary to previous thought, hypercarnivory was relatively rare and potentially secondarily derived."
Most theropods [like the T-Rex] are clearly adapted to a predatory lifestyle, but somewhere on the line to birds, predatory dinosaurs went soft. Once we linked certain adaptations with direct evidence of diet, we looked to see which other theropod species had the same traits, then we could say who was likely a plant eater and who was not.
