American antelope, or pronghorn (Antilocapra americana) are the fastest living land mammal in North America and the last living representative of the family Antilocapridae. Antilocaprids are ruminant artiodactyls that had an extensive fossil record in North America. By the late Pleistocene, there was still a diverse number of pronghorn species in North America. Although both male and female pronghorn have horns that shed seasonally, female’s horns are much smaller.
Although coined the “American antelope,” pronghorn are much more closely related to living giraffes and okapi. Extinct antilocaprids are found from the Miocene, Pliocene, and Pleistocene fossil records across North America.
Distribution and Habitat
Living antilocaprids are found throughout the open habitats of western North America, from Mexico up to southern Canada, preferring open prairie and desert habitats. Some extinct species of antilocaprids can be found further east, as far as Florida.
Antilocaprids are herbivores, foraging on shrubs, flowers, and grasses.
Living antilocaprids are the fastest living land mammal in North America and can reach speeds over 55 mph; however, they are not able to jump or leap very high. It is suggested that pronghorn antelope evolved such high running speeds to outrun the now-extinct American cheetah. Pronghorn fawns are usually born as twins.
Tule Springs Pronghorn
Most antilocaprid genera are identified by the distinctly shaped horn cores on the cranium. Antilocaprid fossils are known from Tule Springs Fossil Beds, but consist entirely of post-cranial bones, so it is unclear which genus of pronghorn inhabited the Las Vegas Valley during the late Pleistocene. Below are some of the possible candidates for the Tule Springs pronghorn:
Many of the early pronghorn fossils collected from Tule Springs fossil beds were questionably referred to the large antilocaprid Tetrameryx, a two-pronged pronghorn which had elongated rear prongs compared to the front prongs. Though roughly the same size as the modern American pronghorn, the limbs of Tetrameryx were a bit more robust, suggesting it did not run as fast as its living relative.
Another common Pleistocene pronghorn was Stockoceros, which is well known from cave sites in the American Southwest and in Mexico. Like Tetrameryx, Stockoceros had a two pronged horn, although the rear prong was about the same height as the front prong. Stockoceros was also roughly the same size as the American pronghorn, but like Tetrameryx, the limbs were much more robust and proportionally shorter. Stockoceros likely wasn’t as fast as the American pronghorn, but it was better adapted to living in rockier or more rugged habitats.
Pleistocene fossil evidence of the American pronghorn has been found from sites in southern Canada, the Rocky Mountain and central states, the American southwest and northern and central Mexico. In Nevada, American pronghorn fossils were found in three cave sites in the northern eastern part of the state.
Capromeryx was a genus of very small pronghorns, reaching shoulder heights of as small as two feet. Their horns grew straight upright, with a much smaller anterior prong compared to the posterior. Fossils of Capromeryx have been recovered from Rancho La Brea in Southern California.