That diagram is a bit funny. Bears and rats are both considered (according to their natural diet) as omnivores, however their teeth couldn't be more different. According to what we know about our ancestors diet, most hominids never been clearly herbi- or frugivores. Even our most closely related "relatives" the chimps are hunting for other primates. (BTW gorillas and orangutans are not meat eaters but they are eating considerable amounts of insects and eggs, so they are also consuming animal proteins.)
Actually the best argument against veganism is the B12 vitamin. Vitamin B12 is an absolutely essential thing, to keep our machine ticking. There are plenty of B12 in meat, but scarce in plants therefore vegans need vitamin supplements. Same thing applies to iron, iodine, zinc, calcium, vitamin D, Omega fatty acids, and so on. So, if being vegan is so natural, fine and dandy and we don't need no stinkin' meat then why they have to take artificial stuff like vitamin and mineral pills?
I think this chart is BS, and the author(s) cherry picked a few things to support their claims, but ignored a lot more what doesn't fit to their views.