I would argue the answer to this question is not so cut and dry. Recent genetic evidence paints a more complicated story, and suggests quite close relationship - at least genetically.
Weinstock et al. 2005. PLOS Biology Evolution, Systematics, and Phylogeography of Pleistocene Horses in the New World: A Molecular Perspective The rich fossil record of horses has made them a classic example of evolutionary processes. However, while the overall picture of equid evolution is well known, the details are surprisingly poorly understood, especially for the later Pliocene and Pleistocene, c. 3 million to 0.01 million years (Ma) ago, and nowhere more so than in the Americas. There is no consensus on the number of equid species or even the number of lineages that existed in these continents. Likewise, the origin of the endemic South American genus Hippidion is unresolved, as is the phylogenetic position of the “stilt-legged” horses of North America. Using ancient DNA sequences, we show that, in contrast to current models based on morphology and a recent genetic study, Hippidion was phylogenetically close to the caballine (true) horses, with origins considerably more recent than the currently accepted date of c. 10 Ma. Furthermore, we show that stilt-legged horses, commonly regarded as Old World migrants related to the hemionid asses of Asia, were in fact an endemic North American lineage. Finally, our data suggest that there were fewer horse species in late Pleistocene North America than have been named on morphological grounds. Both caballine and stilt-legged lineages may each have comprised a single, wide-ranging species. On May 13, 2010, at 10:12 AM, James J. Roper wrote: You do remember that the horses that went extinct in North America are not the same ones that came back with the Spaniards? So, yes, they are introduced. However, horses are not really the issue with introduced species, although they are causing animated debates in the few states that have feral herds. On Thu, May 13, 2010 at 10:16, Randy K Bangert <bangr...@isu.edu<mailto:bangr...@isu.edu>> wrote: Are horses exotic or native if they evolved in North America and then subsequently reintroduced? ====================================== Randy Bangert C. Josh Donlan MA PhD Director, Advanced Conservation Strategies | http://www.advancedconservation.org Fellow, Cornell University | http://www.eeb.cornell.edu/donlan M: +1 (607) 227-9768 (GMT-6) E: jdon...@advancedconservation.org<mailto:jdon...@advancedconservation.org> P: P.O. Box 1201 | Midway, Utah 84049 USA u
