Antelopes are mammals and they are ungulates, meaning they have hooves. Essentially, hoofed animals stand on their third and fourth toes, where have evolved a tough, anesthetic, keratinized outgrowth. Artiodactyla is a subset of ungulates that have even-toed hooves, and antelopes belong to this group along with sheep, goats, cattle, giraffes, deer and pigs. Horned Artiodactyla are a subset that excludes, for example, pigs. The vast diversity of antelopes is separated as a class from other horned Atriodactyla by a set of characteristics: nonbifurcating horns that are not shed, ruminating guts and horizontal pupils.
The great majority of antelopes are native to the African continent. The majority of African antelopes are grass-grazers that live in the African savanna. The animal commonly called a pronghorn antelope in the Western United States is not a true antelope. The few non-African species of antelope are in India, the Arabian Peninsula, Southern Russia and Southeast Asia. Many of the grass-grazing antelope species migrate annually, though some species of antelope have adapted to high mountains, low wetlands and thick forest. Several species of African antelope, including the Blackbuck, Nilgai and Gemsbok, have established themselves in Texas after escaping from exotic-animal hunting compounds maintained for the entertainment of wealthy clients.
The most numerous species in Africa include the wildebeest -- known for its spectacularly dramatic migrations --- the waterbuck, the eland, the tsessebe, the gerenuk, the steenbok, the impala, the springbok, the klipspringer, the sable antelope, the kudu, the oryx, the lechwe and the nyala. The largest antelope is the eland, resembling in many respects an ox. The smallest antelope is found in the Serengeti scrub, named the dikdik. The dikdik weighs about 12 pounds at adulthood.
Extinction threats against various species are attributed to two things: human encroachment on habitat and hunting. The latter is believed to be the greatest threat. Among the 25 threatened species, the five most critically threatened are the Dama Gazelle, the Addax, the Aders' Duiker, the Hirola and the Saiga Antelope. One species is already extinct in the wild, and holding on only through captive breeding pairs. That species is the scimitar-horned oryx.