Taxonomy and notes on the paleobiology of the late Pleistocene (Rancholabrean) antilocaprids (Mammalia, Artiodactyla, Antilocapridae) from the state of Hidalgo, central Mexico

A set of cranial and dental material of Antilocapridae was recovered from Quaternary deposits that outcrop in southeastern Hidalgo, central Mexico. The fossil bearing unit consists of clay, silt, sand, and scarce conglomeratic lenses in a fluvial environment; the specimens are associated with Bison indicating a Rancholabrean Land Mammal Age. The comparative study of the material with selected specimens of North American antilocaprids, allowed its identification as the small-sized species Capromeryx minor and the medium-sized Stockoceros conklingi. The sample referable to C. minor shows a combination of cranial and dental characters typical of this species, including a large posterior tine that is curved upward and forward, posterior horn core with a deep sulcus on its posterior side that extends from the base to the tip, and well-developed heel on M3. The isotopic analysis of teeth referable to this species from Hidalgo indicates a mixed feeding dietary behavior. A partial skull and associated horn core fragments were assigned to Stockoceros conklingi, considering its larger size than C. minor and shorter than the extant pronghorn Antilocapra americana, as well as for having symmetrical and diverging horn cores, and more outwardly flaring horn cores. The recognition of these antilocaprids in southeastern Hidalgo represents one of the southernmost occurrences within temperate North America. The tiny Capromeryx minor is known in North American localities of lower altitude (0-100 m a.s.l.) compared to those of the medium-sized Stockoceros conklingi (1000-2000 m a.s.l.). Hence, body size differences between both species and altitude differences between some of their localities suggests minimal direct competition between these antilocaprids.