The dietary regimes of two contemporaneous populations of Hippotherium primigenium (Perissodactyla, Equidae) from the Vallesian (Upper Miocene) of Southern Germany

Abstract

The first occurrence of tridactyl, hipparionine horses is presently constrained in Eurasia between 11.2 and 10.8 Myr. Hippotherium primigenium is the only species recorded up to now in the early Vallesian–early Turolian of Germany. Two Vallesian populations of H. primigenium are investigated with respect to their trophic regimes. One of these populations derives from the deposits of the Upper Miocene Rhine river exposed at the locality of Eppelsheim (Germany). The other population (Höwenegg) is represented by lacustrine deposits of a former crater lake about 180 km south of Eppelsheim. Both localities represent two almost contemporaneous Vallesian (MN9) populations of a single equid taxon (H. primigenium) from different geographic regions within western Germany. Trophic regimes are reconstructed using the mesowear method [Fortelius and Solounias, Am. Mus. Novit. 3301 (2000) 1–36] and the derived ‘extended’ mesowear method [Kaiser and Solounias, Geodiversitas (2003), in press]. These analyses lead to the identification of a recent trophic reference taxon for each of the two hipparion populations. The common waterbuck (Kobus ellipsiprymnus), a grazer inhabiting reed beds and also foraging into woodlands is identified as the trophic analog for the Eppelsheim population. The reference taxon of the Höwenegg population is the Sumatran rhinoceros (Dicerorhinus sumatrensis), a browser, inhabiting mainly hilly country and preferring saplings, fruit, leaves, twigs, and bark as major food items. The marked differences in the trophic regimes found for the two populations of H. primigenium are interpreted as reflecting the range of possible dietary regimes, here termed the trophic spectrum of this equid species. The trophic signal of H. primigenium is therefore interpreted as an ecological signal reflecting properties of the habitat. The paleohabitat of Eppelsheim would then be recognized as representing at least seasonally extended grassy areas such as reed flats in the proximity of the Miocene Rhine river. The paleohabitat of the Höwenegg, however, was most likely an immediate part of the subtropical mesophytic forests, that covered large parts of Central and Western Europe, Central Asia and southern China during the Vallesian period.