Somewhat related to this. I've already decided that both orcs and humans are subspecies of homo sapiens (homo sapiens praepotens and homo sapiens perpessio, respectively, because both species are abundant and it would be rude to call one of them the "real" homo sapiens). I have fauns/satyr type beings instead of elves, though, because I dislike the idea of an immortal species.
Unlike fauns and satyrs of myth, these guys have about the same hair distribution as humans (i.e., no goat legs). I'd also like to give them antlers instead of horns – that is, they'd be cast off annually, able to be cut off without bleeding to death. Their stance is digitigrade, with solid hooves, as in a horse.
Obviously, having hooves, they're not as closely related as humans and orcs are, and are almost definitely not in the "homo" category. Where might a species like this plausibly fit on a taxonomic tree? And, on a similar note, can I plausibly give my satyrs "horns"?