I'm curious: how do they know it's a new species? Seems like it could just as easily be a small mutation that does not affect interbreeding. From one (presumabl

I'm curious: how do they know it's a new species? Seems like it could just as easily be a small mutation that does not affect interbreeding. From one (presumably dead) specimen, how did they determine it was an entirely new species, and not just a local population?