Dietary resource partitioning in ruminant communities of Miocene wetland and karst palaeoenvironments in Southern Germany

Ruminants made up a major component in Early and Middle Miocene European land mammal faunas. Hypotheses are tested which concern the diversity of feeding niches in Miocene ruminants and their resource partitioning. Because teeth are the basis of taxonomic work in the biota investigated here, the tooth-based mesowear method of dietary evaluation is applied. Dental wear equilibria as evaluated using mesowear analysis represent an immediate taxon-independent habitat: interface, which bridges extant and Neogene communities. Two adjacent palaeoenvironments have been selected as models for testing our hypotheses, because ruminants are well recorded, the temporal window represents a long lasting and stable period before the onset of a global and regional environmental change that led to an increase of grass-dominated environments and because both environments represent fundamentally different habitat conditions but are spatially connected and represent the same climatic zone (i.e., the Molasse Basin wetland and the adjacent karstified Jurassic limestone plateau in Southern Germany). The ruminant communities of both biomes are brachydont throughout and a prevalence of browsing ruminants is found in both biomes, which is in accordance with isotope data. Both habitats, however, did also support strategies equalling those of extant mixed feeders. Among these mixed feeders, there are more grass-dominated mixed feeders in the karst habitat than there are in the wetland. The ruminant communities are thus found to apparently support a range of feeding traits, not evidenced by other ecomorphological approaches such as tooth crown height evaluation nor taxonomic uniformitarianism, The presence of these feeding types suggests that niche segregation in Lower and Middle Miocene brachydont ruminants was already fairly pronounced and reflects the hypothesised niche availability in the two palaeobiomes. The comparatively dry karstified landscape of the Jurassic limestone plateau is reflected by a higher diversity in abrasive feeders compared to the Molasse Basin wetland. As a second approach, two cervid species that co-occur in both biomes, Lagomeryx parvulus and L. pumilio have been tested in terms of differences in the abrasiveness of their diet in the two biomes. L. pumilio has a large dietary spectrum, and in the karst biome, it shows a signal equalling that of extant grass-dominated mixed feeders, while in the wetland biome it behaves as a browser as many other taxa also do. L. parvulus is shown to have a much less pronounced flexibility, as its diet consists of browse in both biomes. The coincidence of both, community structure and interspecific variability in dietary traits of the Lagomeryx species is a strong argument to consider the central hypothesis as supported, that drier environments result in more abrasion dominated dietary signals of flexible feeders, and that there is a general relationship between habitat structure, food availability, the abrasiveness of the forage, and tooth wear. The dietary variability of a species therefore seems to be a highly indicative characteristic in any ecological analysis of extant and fossil biomes and the presented approach adds rarely gained information on certain fossil members of a palaeocommunity and their potential role in the ecosystem. (c) 2007 Elsevier B.V. All rights reserved.