The Antilocapridae are a family of artiodactyls endemic to North America. Their closest extant relatives are the giraffids with which they comprise the superfamily Giraffoidea. Only one species, the pronghorn (Antilocapra americana), is living today; all other members of the family are extinct. The living pronghorn is a small ruminant mammal resembling an antelope. Description In most respects, antilocaprids resemble other ruminants. They have a complex, four-chambered stomach for digesting tough plant matter, cloven hooves, and small, forked horns. Their horns resemble those of the bovids, in that they have a true horny sheath, but, uniquely, they are shed outside the breeding season, and subsequently regrown. Their lateral toes are even further diminished than in bovids, with the digits themselves being entirely lost, and only the cannon bones remaining. Antilocaprids have the same dental formula as most other ruminants: . Classification The antilocaprids are ruminants of the clade Pecora. Other extant pecorans are the families Giraffidae (giraffes), Cervidae (deer), Moschidae (musk deer), and Bovidae (cattle, goats and sheep, wildebeests and allies, and antelopes). The exact interrelationships among the pecorans have been debated, mainly focusing on the placement of Giraffidae, but a recent large-scale ruminant genome sequencing study suggests Antilocapridae are the sister taxon to Giraffidae, as shown in the cladogram below. Evolution The ancestors of pronghorn diverged from the giraffids in the Early Miocene. This was in part of a relatively late mammal diversification following a climate change that transformed subtropical woodlands into open savannah grasslands. The antilocaprids evolved in North America, where they filled a niche similar to that of the bovids that evolved in the Old World. During the Miocene and Pliocene, they were a diverse and successful group, with many different species. Some had horns with bizarre shapes, or had four, or even six, horns. Examples include Osbornoceros, with smooth, slightly curved horns, Paracosoryx, with flattened horns that widened to forked tips, Ramoceros, with fan-shaped horns, and Hayoceros, with four horns. Species Subfamily Antilocaprinae Tribe Antilocaprini Genus Antilocapra Antilocapra americana - pronghorn A. a. americana - Common pronghorn A. a. mexicana - Mexican pronghorn A. a. peninsularis - Baja California pronghorn A. a. sonoriensis - Sonoran pronghorn A. a. oregona - Oregon pronghorn †Antilocapra pacifica Genus †Texoceros Texoceros altidens Texoceros edensis Texoceros guymonensis Texoceros minorei Texoceros texanus Texoceros vaughani Tribe †Ilingoceratini Genus †Ilingoceros Ilingoceros alexandrae Ilingoceros schizoceros Genus †Ottoceros Ottoceros peacevalleyensis Genus †Plioceros Plioceros blicki Plioceros dehlini