Antilocapra americana—Pronghorn // Capromeryx—Miniature Pronghorns // Stockoceros—Stock's and Quentin's Pronghorns // Tetrameryx—Four-horned Pronghorns
The family is endemic to North America, with one living species (Antilocapra americana). However, its fossil record is relatively rich from the Miocene until the end of the Pleistocene when several genera became extinct.
Although sometimes placed in the Bovidae, current practice by most is to keep the Pronghorn in its own family. They share with the bovids the possession of non-deciduous horn cores of bone that are covered by the keratinous horn in life; they differ from all bovids, however, in that the horn sheath is deciduous and branched. The living Pronghorn is exquisitely adapted for cursorial life, including highly successful respiratory and circulatory systems that allows long-distant rapid locomotion. The Pronghorn is considered to be North America's fastest terrestrial mammal. The morphological characters of the extinct Pleistocene forms show osteological adaptations mostly similar to those of the Pronghorn. Molars are highly hypsodont in our representatives, although the modern Pronghorn is not primarily a grazer.
Fig. 1. Male Antilocapra americana, Chihuahuan Desert of Texas. Note the prong coming from the anterior surface of the horn. Photograph by Lauri Lear.
The various species are defined largely on the basis of horn core characteristics, although size also plays a part. Antilocapra americana possesses a single, unbranched horn core on each side (although the horn itself is branched); the other two genera within our area have two horn cores on each side rising from a common area of the frontal bone more or less above the orbit. Capromeryx horn cores consist of a very small anterior fork and a larger posterior fork; those of Stockoceros are subequal with the hind fork somewhat larger. Although two species of the latter genus have been listed for our region, only S. conklingi is recognized here (see the Stockoceros account for justification).
Fig. 2. Phalanges of the three genera of Pleistocene antilocaprids in our region. Top row, Antilocapra americana; middle row, Stockoceros conklingi; bottom row, Capromeryx sp. From left to right, lateral views of phalanx III, ventral views of phalanx II, and ventral views of phalanx I. Phalanx III of Capromeryx is reversed for comparison. Scale in mm. UTEP specimens.
Horn cores are relatively rare in fossil deposits; thus identification usually is on the basis of size, with Antilocapra largest, followed by Stockoceros, and then by the diminutive pronghorns, Capromeryx. With size being of importance in identification, measurements from the literature and this work are listed.
Last Update: 24 May 2014