The first species to be named was found in the Miocene Mascall Fauna of Cottonwood Creek, Oregon. Named "Anchitherium ultimus" the species was described in 1886 by noted paleontologist, E. D. Cope during the height of the Bone wars. During study 1906 on the Mascall formation equids, J. Gidley moved to a new genus he named "Archaeohippus". The strong similarity of the traits resulted in the genus being considered a subgenus of "Parahippus" by W. D. Matthew in 1932. In stark contrast of opinion "Archaeohippus" was revalidated by D.F. Bode in 1933, and along with "A. ultimus", he included "A. mourningi" and "A. penultimus". "Archaeohippus" ranged across all of North America. In addition to the occurrences in Florida and Oregon, fossil specimens have been found in Southern Saskatchewan, Canada. At the other end of its range "Archaeohippus" have been found as far south as the Miocene Gaillard Cut local in the former canalzone of Panama. ""Archaeohippus" stenolophus", known from Oligocene deposits in Saskatchewan, does not belong in "Archaeohippus", and "A. minimus" is a composite of two taxa, as noted by Osborn (1918), with the P3-M1 belonging to "A. ultimus" and the molar and premolar belonging to a larger, more derived equid. "Archaeohippus mannulus" and "Arachaeohippus blackbergi" have been unearthed in Florida, specifically at the Thomas Farm Site.