Neue Deutungen zur Systematik und Palaeoökologie der Dorn-Dürkhiem-1-Hipparionen (Ober-Miozän, Turolium [MN11]), Rheinhessen, Deutschland

The Turolian vertebrate locality of Dorn-Dürkheim is situated near the city of Mainz, SW-Germany. The mammalian fauna is significantly younger than most other late Miocene Central European faunas that have yielded an equally rich assemblage of hipparion remains. The Dorn-Dürkheim hipparion fauna consists of isolated teeth and posteranial skeletal elements. We use the Vallesian (MN9) samples of Hippotherium primigenium from Eppelsheim and Höwenegg (Germany) as standards for comparison. Based on cheek tooth occlusal dimensions and continuous variables of the astragali, we identify two clusters of dental and posteranial specimens. We argue that these two clusters belong to two populations of hipparions that differ from one another principally in their body size. We further investigate the populations from Eppelsheim (EPhP), the total of all Dorn-Dürkheim specimens (DDpPall) and the two sub-populations from Dorn-Dürkheim (DDhPri and DDhPsm) with respect to their dietary preferences. For this we use the microwear and mesowear methods. The paleodietary signals for each sub-population are found to be quite different. The larger sized population of Dorn-Dürkheim (DDhPri) was a mixed feeder, while the small sized population (DDhPsm) is interpreted to have been a dedicated browser. In addition, we redefine the calculation of indices of hypsodonty so that they are more appropriate to equine horses. In comparing the hypsodonty indices of the hipparion populations from Eppelsheim and the total of the Dorn-Dürkheim specimens we find no differences in hypsodonty. In our comparison of Dorn-Dürkheim metacarpal III's (MC III's) with MC III's from other pertinent European localities, we find two MC III's from Dorn-Dürkheim to be similar to the Höwenegg population of H. primigenium. However, eight Dorn-Dürkheim specimens differ from the Höwenegg population in having a relatively expanded crisis sagittalis and reduced lateral and medial condyles. The only complete Dorn-Dürkheim MC III is relatively longer than the those from the Höwenegg population. This leads us to conclude that the MC III morphology of the smaller sized sub-population from Dorn-Dürkheim (DDhPsm) exhibits an adaptation for more cursorial locomotion than the Höwenegg hipparions, while the larger sized sub-population ventured into less forested habitats and was less cursorial. Based on the peculiarities of metapodial build and of cheek tooth dimensions, we recognize the population DDhPsm from Dorn-Dürkheim as belonging to a new species of hipparionine horse, Hippotherium kammerschmitti. New species: Cormohipparion n. sp., Hippotherium kammerschmitti n. sp.