African wild ass (Equus)" which diverged ~4.8 (3.2–6.5) million years ago. Different authors consider the African wild ass and the domesticated donkey one or two species; either view is technically legitimate, though the former is phylogenetically more accurate. The species name for the African wild ass is sometimes given as "asinus", from the domestic donkey, whose specific name is older and usually would have priority. But this usage is erroneous since the International Commission on Zoological Nomenclature has conserved the name "Equus africanus" in Opinion 2027. This was done to prevent the confusing situation of the phylogenetic ancestor being taxonomically included in its
Equus conversidens New Mexico, Oklahoma, Kansas and Florida, synonymizing "Equus francisci", "Equus tau", "E. littoralis", "E. achates", and "E. barcenaei" with "E. conversidens". However, Winans (1985) and MacFadden (1992) challenged the validity of "E. conversidens" due to its minimal diagnostic value, and treated "E. francisci" as valid. Subsequent study confirmed the "nomen dubium" status of "E. conversidens" because the holotype was undiagnostic besides its small size. Equus conversidens Equus conversidens (Owen 1869), or the Mexican horse, is a dubious Pleistocene species of horse, now extinct, that inhabited North America. The holotype of "Equus conversidens", a partial palate, was unearthed in Pleistocene deposits