See J. van Wormer, The World of the Pronghorn (1968).
The pronghorn (Antilocapra americana), also pronghorn antelope or prong buck, is a species of ungulate mammal native to interior western North America. It is the only surviving member of the family Antilocapridae.
Each "horn" of the pronghorn is comprised of a slender, laterally-flattened blade of bone which 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; in females, they are either small, misshapen, or absent.
The orbits (eye sockets) are prominent and sit high on the skull; there is never an antorbital pit. The feet have only two digits; no dewclaws are present. The teeth are hypsodont, and the dental formula is I 0/3, C 0/1, P 3/3, M 3/3 x 2 = 32.
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. Females antelope will occasionally grow horns. Males have a horn sheath about 12.5–43 cm (mean 25 cm) long with a prong. Females have smaller horns, ranging from 2.5–15 cm (average 12 cm), and sometimes barely visible; they are straight and very rarely pronged. Males are further differentiated from females in that males will have a small patch of black hair at the corner of the jawbone. Pronghorns have a distinct, musky odor. Males mark territory with a scent gland located on the sides of the head. They also have very large eyes, with a 320 degree field of vision. Unlike deer, pronghorns possess a gallbladder.
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 New World. The top speed is very hard to measure accurately and varies between individuals; it is variously cited as up to 70 km/h, 72 km/h, or 86 km/h. It is often cited as the second-fastest land animal, second only to the cheetah. It can however sustain high speeds longer than cheetahs. The pronghorn probably evolved its running ability to escape from the recently extinct American cheetah, since its speed greatly exceeds that of extant North American predators. It has a very large heart and lungs, and their hair is hollow. 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 barbless bottom wire.
Pronghorns were brought to scientific notice by the Lewis and Clark Expedition, which found them in what is now South Dakota, USA. The range extends from southern Saskatchewan and Alberta in Canada south through the United States (southwestern Minnesota and central Texas west to northeastern California), to Sonora and San Luis Potosí in northern Mexico, with a small disjunct population in northern Baja California Sur.
The subspecies known as the Sonoran pronghorn (Antilocapra americana sonoriensis) occurs in Arizona and Mexico. Other subspecies include the Mexican Pronghorn (A. a. mexicana) and the critically endangered Baja California Pronghorn (A. a. peninsularis).
Bands of pronghorns live in open grasslands, forming small single-sex groups in spring and summer, and gathering into large mixed herds, sometimes up to 1,000 strong, in the fall and winter; they may migrate up to 160 km to avoid deep winter snow.
Pronghorns are now numerous enough that they exceed the human population in all of Wyoming and parts of northern Colorado. It is widely hunted in western states for purposes of population control and food, as the meat is rich and lean.