Dietary ecology of mixed-feeding antelopes in the Omo-Turkana basin during the Plio-Pleistocene: a tool to investigate hominin palaeo-environments.

Abstract

To assess whether detailed studies of the dietary ecology of mixed-feeding antelope species could be used to investigate hominin palaeo-environments in the Omo-Turkana basin during the Plio-Pleistocene (3.5-1.6 Ma), a detailed study of the dietary ecology of mixed-feeding antelopes was proposed. This research focused on the diets of the impala (genus Aepyceros) and the springbok (genus Antidorcas), whose extant relatives demonstrate a high dietary plasticity. The dietary ecology of these taxa was evaluated through stable carbon and oxygen isotope, mesowear and dental microwear textural analyses. To provide more tools to interpret fossil evidence, predictive models were tested to study the relationship between land cover and dietary behaviours of modern populations. The high variability of stable carbon isotope values observed across modern impala specimens and the wide range of habitat types they were associated with showed that impalas tend to rely heavily on palatable grasses and forbs, suggesting a preference for herbaceous plants. The diet of modern impalas therefore does not always reflect the vegetation types prevailing in their environments, as availability of their preferred foods can be influenced by local year-round land cover patterns and by seasonal fluctuations in climate. However, the predictions generated for fossil Aepyceros samples for the Omo-Turkana basin were consistent with previous palaeo- environmental studies for this region, demonstrating the potential of this method and the relevance of using these taxa as palaeo-environmental indicators. Significant differences in dietary ecology were observed for the studied taxa when comparing assemblages from different fossil localities, as well as when comparing assemblages between members. Results suggested the presence, across all three fossil localities of the Omo-Turkana basin, of long-lived mosaic habitats, which could have supported a high diversity of mammalian taxa with varying ecological requirements. Results confirmed previous studies which suggested patterns of grassland expansion and increased habitat fragmentation in the region from ~2.0 Ma, as well as an increase in seasonal and interannual rainfall variability between 2.27 and 1.9 Ma. Such conditions have been previously hypothesized to have influenced local faunal biodiversity in the region, adding selective pressures associated with seasonal changes in resources abundance and distribution, acting, in turn, as an additional driver of hominin evolution.