Pronghorn

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 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 five existed when humans entered North America^{[citation needed]} and all but A. americana are now extinct.

Adult males are 1.3–1.5 m (4 ft 3 in–4 ft 10 in) long from nose to tail, stand 81–104 cm (32–41 in) high at the shoulder, and weigh 36–70 kg (79–150 lb). The females are the same heights as males but weigh 41–50 kg (90–110 lb). The feet have just two hooves, with nodewclaws. The body temperature is 38 °C (100 °F).Each "horn" of the pronghorn is composed of a slender, laterally flattened blade of bone that grows from the frontal bones of the skull, forming a permanent core. As in the Giraffidae, skin covers the bony cores, but in the pronghorn it develops into a keratinous sheath which is shed and regrown on an annual basis. Unlike the horns of the family Bovidae, the horn sheaths of the pronghorn are branched, each sheath possessing a forward-pointing tine (hence the name pronghorn). The horns of males are well developed.

The orbits (eye sockets) are prominent and sit high on the skull; there is never an antorbital pit. Males have a prominent pair of horns on the top of the head, which are made up of an outer sheath of hairlike substance that grows around a bony core; the outer sheath is shed annually. Males have a horn sheath about 12.5–43 cm (4.9–17 in) (average 25 cm (9.8 in)) long with a prong. Females have smaller horns, ranging from 2.5–15 cm (1–6 in) (average 12 centimetres (4.7 in)) and sometimes barely visible; they are straight and very rarely pronged.^[8] Males are further differentiated from females in that males will have a small patch of black hair at the angle of the mandible. Pronghorns have a distinct, musky odor. Males mark territory with ascent gland located on the sides of the head.^[5] They also have very large eyes, with a 320 degree field of vision. Unlike deer, pronghorns possess a gallbladder.^[10]

It can run exceptionally fast, being built for maximum predator evasion through running, and is generally accepted to be the fastest land mammal in the Western Hemisphere. The top speed is very hard to measure accurately and varies between individuals; it is variously cited as up to 70 (43),^[7], 86 (53)^[8], or 100 km/h (62 mph)^[11][12].It is often cited as the second-fastest land animal, second only to the cheetah.^[13] It can, however, sustain high speeds longer than cheetahs.^[6] University of Idaho zoologist John Byers has suggested that the pronghorn evolved its running ability to escape from extinct predators such as the American cheetah, since its speed greatly exceeds that of extantNorth American predators.^[6][14] It has a very large heart and lungs, and hollow hair. Although built for speed, it is a very poor jumper. Their ranges are often affected by sheep ranchers' fences. However, they can be seen going under fences, sometimes at high speed. For this reason the Arizona Antelope Foundation and others are in the process of removing the bottom barbed wire from the fences, and/or installing a barb-less bottom wire.^{[citation needed]}

The pronghorn has been observed to have at least 13 distinct gaits, including one reaching nearly 7.3 m (8 yards) per stride.