I also saw this back on April1st (didn't get around to post about it in the meantime), thought for a second it was an April Fool's hoax, but it wasn't (and yes, I've heard of Elasmotherium before ). From a perspective of their relationship inside the mammals, both horses and rhinos are odd-toed ungulates (hooved animals), or Perissodactylia. So in away the prehistoric Elasmotherium is a unicorn in more than one way.