ERode said
BUT IT MAKES SO MUCH SENSE!We know that Grimm are attracted to things with souls, and would aim to eat humans. If we then extrapolate and assume Grimm gain their animal motifs because that's what they've consumed before (lesser souls in the form of animals/wildlife) then the Faunus could have popped up shortly before the advent of Dust, in the form of super-strong Grimm who have eaten enough humans to gain a soul of their own and a human-ish form!
I would assume they would be able to reproduce because the amount of Faunus in the world, I suppose, rivals that of the humans. If what you say is true, that would mean a lot, a lot, a lot of dead humans. But, I feel like, if this theory were true, we'd assume Faunus either lose all kinds of memories prior to their 'birth' and that, after their initial transformation, are able to breed among each other. :o The only technical species that doesn't have to go through bouts of incest just to get their numbers at a stable rate. Lolololol.
EDIT: Maybe this could be like... a sort of... like... plot point? Or something? And then it's like... everyone looks at the Faunus in a worse light. D: Or maybe pepples are like, "We must hid dis." Would tear a considerable rift between team members and stuffs.