The last Plio-Pleistocene hipparions of Western Eurasia. A review with remarks on their taxonomy, paleobiogeography and evolution

The Pliocene and Early Pleistocene three-toed horses of Western Eurasia (Caucasus, Anatolia, Balkans, Eastern and Central Europe, Italian and Iberian Peninsulas and England) have been studied since the second half of the 19th Century, leading to different interpretations of their taxonomy and evolution. Herein we provide a revision of the taxa from these countries, based principally on the large equid samples from the localities of Villarroya (Iberian Peninsula) and Kvabebi (Georgia). The equid samples from these two localities are compared to a large suite of Old World hipparions from Late Miocene to Early Pleistocene, to identify the diverse genera and species occurring in the Pliocene and Early Pleistocene from the Caucasus to the Iberian Peninsula. Moreover, we provide a revised interpretation of their taxonomy, chronology, paleobiogeography and evolutionary history. During the Plio-Pleistocene, we recognize the presence of three genera and six species (Cremohipparion sp., Proboscidipparion heintzi, Proboscidipparion crassum, Plesiohipparion longipes, "Plesiohipparion" fissurae and Plesiohipparion rocinantis) with a different distribution in time and space for these lineages in the Pliocene and Early Pleistocene.