The Pronghorn (Antilocapra americana) is a species of artiodactyl mammal endemic to interior western and central North America. Though not an antelope, it is often known colloquially in North America as the Prong Buck, Pronghorn Antelope, or simply Antelope,[3] as it closely resembles the true antelopes of the Old World and one theory is that it fills a similar ecological niche due to convergent evolution.[4] It is the only surviving member of the family Antilocapridae.[5] During the Pleistocene period, 12 antilocaprid species existed in North America.[6] About 5 existed when humans entered North America[citation needed] 13,000 years ago; all but A. americana are now extinct.[5]