The pronghorn is a mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American antelope, prong buck, pronghorn antelope and prairie antelope, because it closely resembles the antelopes of the Old World and fills a similar ecological niche due to parallel evolution. It is the only surviving member of the family Antilocapridae. As a member of the superfamily Giraffoidea, the pronghorn’s closest living relatives are the giraffe and okapi. The Giraffoidea are in turn members of the infraorder Pecora, making pronghorns more distant relatives of the Cervidae (deer) and Bovidae (cattle, goats, sheep, antelopes, and gazelles), among others.
The pronghorn is the fastest land mammal in the Western Hemisphere, being built for maximum predator evasion through running. The top speed is dependent upon the length of time over which it is measured. It can run 35 mph for about 4 mi and up to 55 mph 1⁄2 mi). While it is often cited as the second-fastest land animal, second only to the African cheetah, it can sustain high speeds longer than cheetahs. The pronghorn may have evolved its running ability to escape from now-extinct predators such as the American cheetah, since its speed greatly exceeds that of all extant North American predators. Compared to its body size, the pronghorn has a large windpipe, heart, and lungs to allow it to take in large amounts of air when running. Additionally, pronghorn hooves have two long, cushioned, pointed toes which help absorb shock when running at high speeds. They also have an extremely light bone structure and hollow hair.
Pronghorns are built for speed, not for jumping. Since their ranges are sometimes affected by sheep ranchers’ fences, 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.