The results are in sharp contrast to a widespread belief among paleontologists who say theropod dinosaurs sought their prey.Lindsay Zanno and Peter Makovicky of the Field Museum in Chicago used statistical analysis to conclude that 90 species of theropod dinosaurs ate a plant-based diet, particularly among coelurosaurs, the mainly bird-like dinosaurs.
The results were in sharp contrast to a widespread faith among paleontologists who say theropod dinosaurs hunted their prey, particularly those closest to the ancestors of birds.
"Most theropods are obviously adapted to a predatory lifestyle, but someplace on the line to birds, predatory dinosaurs went soft," Zanno explained.
Zanno and Makovicky found almost two dozen anatomical features were statistically linked to direct facts of plant eating among coelurosaurian dinosaurs, such as the loss of teeth or a long neck.
"Once we linked convinced adaptations with direct evidence of diet, we appeared to see which other theropod species had the same traits... Then we could say who was expected a plant eater and who was not," added Zanno.
During their analysis, the researchers establish that 44 theropod species distributed across six major lineages ate plants and that the ancestor to most feathered dinosaurs and modern birds had most likely already stopped eating meat only during the Cretaceous Period, some 145-65 million years ago.
In light of the huge number of plant eaters during that period, the carnivorous diet of T. rex, Velociraptor and other meat-eating coelurosaurs should be viewed "more as the exception than the rule," Zanno said.
"It’s time to start considering these animals in a new evolutionary context," Zanno said.
The researchers also recommended that these large predators and their close relatives may have in fact evolved from omnivorous ancestors.
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