Teeth. Most carnivore teeth are unsuited for a diet of vegetation.
I’m with you on the assessment of skulls, teeth structure and likely diet. However, it is not 100% certain, and it irritates me when conjecture is stated as fact by so called scientist. If they would simply condition it with “we believe” or “I think” or “it is reasonable to assume”, we would all enjoy the opportunity to exercise our critical thinking skills. However, when stated as fact, especially to schoolchildren, they accept it verbatim, and fall into all sorts of error and wacky beliefs. Fairy tales like abiogenesis, global warming and liberalism are destroying this once great nation.