Dumb question. How do we know it's a new species and not just humans with particular genetic traits? For example, if a million years from now, someone was to d

Dumb question. How do we know it's a new species and not just humans with particular genetic traits? For example, if a million years from now, someone was to dig up a bunch of bones from a dog kennel, what would they make of all the different bones from Irish wolfhounds down to sausage dogs?