The paleoenvironmental context of the Early and Middle Pleistocene at Melka Kunture archaeological site (Upper Awash Valley, Ethiopia), as evidenced by stable isotope analysis

Abstract

Stable isotope analysis is a well-established and powerful tool for determining valid information on paleodiet, paleoenvironment, and paleoecology (Bibi et al. 2013; Bocherens et al. 1996; Cerling et al. 2015; Lee-Thorp et al. 2010; Levin et al. 2008; Rivals et al. 2018). This method has been widely applied to Pleistocene archaeological sites in eastern Africa at medium and low altitudes (Ascari et al. 2018; Bedaso et al. 2010; Negash et al. 2020; Rivals et al. 2017; Semaw et al. 2020; Uno et al. 2018); however, the literature lacks isotopic reconstructions of ecological conditions at high elevations. Here, are reported the carbon and oxygen stable isotope compositions (13C, 18O) of fossil teeth enamel (carbonates) from the Melka Kunture (MK) prehistoric site, located in the Ethiopian highland (~2000 m a.s.l.), in order to provide paleoenvironmental insights. The 13C/12C and 18O/16O isotopic ratios were measured on 178 fossil teeth representing a various range of taxa (Hippopotamidae, Bovidae, Equidae, Suidae, Giraffidae, and Crocodylidae) to determine the extent of the vegetation types. Collectively, 310 enamel samples (bulk and intra-tooth) were analyzed. The carbon isotopic results of hippopotamids, bovids, equids, suids, and giraffids indicate a range of foraging strategies across the pure C4 diets to mixed C3-C4 diets, with variations between ~1.95 Ma and ~0.6 Ma (Mega annum) (Early and Middle Pleistocene). In contrast, the bulk and intra-tooth carbon isotopic ratios of crocodiles suggest that these Pleistocene reptiles ate herbivores that consumed C3 plants. The intra-tooth results of hippo, equid, and suid teeth indicated C4 diets and stable water conditions during the lifetime of the sampled mammals. The isotopic data, which emphasize the presence of open space conditions such as C4 high-elevation grasslands, are consistent with pollen and phytolith analysis, indicating extended mountain grasslands, with a different abundance of mesophytic grasses, mountain forests, woodlands, and bushlands. However, it should be kept in mind that isotopic results from teeth enamel reflect the feeding strategies and the ecological behaviour of the analyzed taxa, while fossil pollen allows describing the plant types present even at a certain distance from the site, and phytolith data allow characterizing the distribution of the “on the spot” plants at the time of deposit formation. These complementary data encourage a combined approach among distinct methods that can yield more detailed paleoenvironmental and ecological insights.