Our findings detect 21 morphological features that exhibit statistically significant correlations with extrinsic fossil evidence of coelurosaurian herbivory, such as stomach contents and a gastric mill. ... The distribution of these features suggests that herbivory was widespread among coelurosaurians, with six major subclades displaying morphological evidence of the diet, and that contrary to previous thought, hypercarnivory was relatively rare and potentially secondarily derived.It's not exactly a "vegetarian T. rex," but it's interesting nonetheless.
Zanno & Makovicky. 2010. Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution. PNAS DOI 10.1073/pnas.1011924108.
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