Article: The Miocene horse Hipparion from North America and from the type locality in southern France
The three-toed horse Hipparion is diagnosed by the presence of a preorbital facial fossa that anteriorly is poorly defined and posteriorly is moderately pocketed with a well-developed and continuous rim. The concept of the genus Hipparion sensu stricto (s.s.) is presently restricted in the Old World to H. prostylum from the genotypic locality at Mt. Leberon, France, and the species H. tehonense and H.forcei from New World localities with a similar configuration of the preorbital facial fossa. It has previously been stated that, although Hipparion was common in the Old World Neogene, this genus was very rare in equivalent-aged sediments in the New World. Based on the concept of the genus presented here, Hipparion s.s. is found at numerous New World localities. There apparently was a generic-level continuity of Hipparion s.s. that existed throughout Holarctica during part of the Neogene. Hipparion horses (sensu lato) appear to represent a polyphyletic assemblage of several genera that arose independently from more than one merychippine ancestor during the Miocene. The presence of hipparion horses in the New and Old Worlds probably resulted from more than one dispersal event across Beringia.