Combining stable isotopes and ichnological evidence: the case study of Hippopotamus cf. amphibius from Melka Kunture (Upper Awash, Ethiopia)

Melka Kunture is a rich complex of prehistoric sites located on the margin of the Main Ethiopian Rift between 2000 and 2200 m above sea level. It provided abundant Pleistocene lithic tools, faunal and hominin remains within a high-elevation environment, with vegetation belonging to the Dry evergreen Afromontane Forest and Grassland Complex. In this context, Hippopotamus cf. amphibius is widely attested and dominates the faunal assemblage. Hippo activity and behavior are exceptionally recorded in several ichnological horizons, whereas cut-marks on a hippo’s scapula and tibia prove the hominin-hippo interaction. Furthermore, ichnological evidence proves that hominins and hippos have shared the same areas. In this paper, we combine stable carbon and oxygen isotope analysis and ichnological evidence of hippos from the Melka Kunture sequence to reconstruct the hippo diet, habitat, and behavior. Our results indicate that during the Early and Middle Pleistocene at sites dated between 1.95 Ma and 0.68 Ma, hippos mostly consumed C4 plants, although they also fed on C3 vegetation. This feeding strategy is consistent with previous isotopic studies in other archaeological sites, which concluded that hippos are more versatile and opportunistic feeders than full grazers. In addition, the elevation of Melka Kunture is a significant factor when observing stable carbon isotopic values of tooth enamel because the C3 signal may also reflect the proportion of C3 plants and grasses, as evidenced by pollen and phytolith analyses. Furthermore, hippo fossil footprints, trackways, and a trail described exceptional and well-preserved evidence of Pleistocene hippo anatomy and behavior that are consistent with observations of the modern hippo species. Our analysis offers a complementary perspective for reconstructing the environment available to the hominins in the area during the Pleistocene.