The North American pronghorn (Antilocapra americana) is the surviving member of a group of animals that evolved in North America during the past 20 million years. It is not a true antelope, which is found in Africa and southeast Asia. The use of the term “antelope” seems to have originated when the first written description of the animal was made during the 1804–1806 Lewis and Clark Expedition.
The pronghorn has true horns, made of modified, fused hair that grows over permanent bony cores, but they differ from those of other horned animals in two major ways: the sheaths are shed and grown every year and they are pronged. (A number of other horned mammals occasionally shed their horns, but not annually.) Adult males typically have 10–16 inch horns that are curved at the tips. About 70% of the females also have horns, but they average 1–2 inches long and are not pronged. The males usually shed the horny sheaths in November or December and begin growing the next year’s set in February or March. The horns reach maximum development in August or September. Females shed and regrow their horns at various times.
Pronghorn are easy to distinguish from the park’s other ungulates. Their deer-like bodies are reddish-tan on the back and white underneath, with a large white rump patch. Their eyes are very large, which provides a large field of vision. Males also have a black cheek patch.
The running gait of the pronghorn is beautifully smooth and their powerful legs can carry them at a remarkable pace across the roughest kind of terrain. As the fastest North American mammal, pronghorns can reach speeds of 60 miles per hour. At high speed they cover the ground in great strides of 14 to 24 feet, and are known to run for long distances at speeds of 30 to 40 miles per hour.