PLEISTOCENE HORSES FROM TEXAS AND ALASKA: ARE THEY THE SAME?

Fossil morphology and ancient DNA support different conclusions concerning the number of species of fossil horses inhabiting North America during the late Pleistocene. Fossil DNA purports to demonstrate only two species of Equus, one ‘stout-legged’ (Equus ferus) and one ‘stilt- legged’ (Equus NWSL) represented in late Pleistocene North America. Morphological evidence indicates a much greater diversity. In Texas, there are at least two ‘stout-legged’ species (Equus conversidens and E. scotti) and two ‘stilt-legged’ forms (E. francisci and E. calobatus). Equus ferus, the ancestor of domestic horses, is only present at high latitudes. The two named species of North American ‘stilt-legged’ horses, the smaller E. francisci (holotype from Wharton County, Texas) and the much larger E. calobatus (holotype from Briscoe County, Texas) each have more elongate metatarsals than ‘stilt-legged’ horses from Alaska and Wyoming employed in DNA studies. We propose that the limited sample of fossils yielding DNA hampers interpretations of the true diversity of Pleistocene Equus in North America.