Intra-tooth isotopic analysis shows seasonal variability in the high-elevation context of Melka Kunture (Upper Awash Valley, Ethiopia) during the Early Pleistocene

In order to investigate seasonal changes in diet, environment and climate, we analyzed the stable carbon and oxygen isotopic composition of intra-tooth sequential profiles (14 teeth, 282 enamel samples) of Hippopotamidae, Equidae, Bovidae and Suidae from Melka Kunture, Upper Awash Valley, central Ethiopian Highlands (2000–2200 m a.s.l.).

We found that during the Early Pleistocene, between 1.95 and 1 Ma, most of the analyzed hippos display a seasonally stable C₄ diet, even if the δ¹³C values within hippos show a degree of variability that we interpret as the outcome of feeding on plants that use different C₄ photosynthetic pathways. Several hippo specimens display a seasonal shift from C₄ to mixed C₃-C₄ diets. The sampled equid, bovid and suid specimens recorded both stable C₄ diets and mixed C₃-C₄ feeding with a seasonal progressive increase of δ¹³C values. When affected by seasonal changes, the serially analyzed taxa show different niche partitioning: hippos increase the consumption of C₃ vegetation, whereas equids and suids include more C₄ vegetation in their diets. The intra-individual δ¹⁸O variability in the analyzed taxa is interpreted as the outcome of different water sources, depending on animal habitat, behavior and mobility patterns.

Our data are placed in controlled stratigraphic and chronological sequences and combined with the outcome of other proxies, allowing us to evaluate the site paleoecology comprehensively. We suggest that the central Ethiopian Highlands, where MK is located, possibly acted as a refugium-like area during the Early and Middle Pleistocene, characterized by a specific type of montane vegetation (DAF) and diverse faunal and hominin species that demonstrated their resilience and adaptability to changing environments and climates.