PALEOENVIRONMENTAL RECONSTRUCTION BASED ON ISOTOPIC EVIDENCE OF EARLY HOMININ AND HERBIVORE DIETS (KARONGA BASIN, MALAWI)

The development of East African savannas is crucial for the evolution, migration and diet of early hominins. These ecosystems range from closed woodland to open grassland savanna and vary widely in fraction of woody cover, providing a wide range in food supply for hominins.

We focus on Plio-/Pleistocene sediments of the Chiwondo Beds (Karonga Basin, Northern Malawi), which contain fossils attributed to Homo rudolfensis and Paranthropus boisei. The ca. 2.4 Ma old sites are considered to display the earliest coexistence of both species. The Uraha and Malema localities are situated between the well-known hominin bearing sites of today’s Somali-Masai savanna in the Eastern Rift and the Highveld Grassland in southern Africa and therefore fill an important geographical gap for hominin research. We perform stable carbon and oxygen isotope analysis of fossil enamel to draw conclusions about the diet of these early hominins. Additionally, we supplement δ¹³C values from pedogenic carbonate with data from fossil enamel of different herbivore (suids, bovids, equids) species. We complement the former by Δ₄₇ thermometry data as a proxy for soil temperature.

Consistent δ¹³C values around -9 ‰ from pedogenic carbonate and suidae enamel spanning the last ca. 4.3 Ma indicate a C₃-dominated environment in the Karonga Basin. Presence of specialized grazers with more positive δ¹³C enamel values around -1 ‰ is indicative of localized patches of C₄-grassland. The overall fraction of woody cover (60-70 %) near paleolake Malawi reflects higher canopy density in the Malawi Rift than in the Eastern Rift. The discrepancy between the two savanna types increases since the Late Pliocene, when the Somali-Masai ecosystem started to show clear evidence for an open, C₄-dominated landscape. Therefore, the evolution of East African ecosystems follows different patterns along the rift axis.

The appearance of C₄-grasses is considered as a driver of evolutionary faunal shifts, but despite the difference of ecosystem evolution, similar hominins occurred in both landscapes, pointing to distinct habitat flexibility and may also indicate nutritional versatility. Analyzed Paranthropus boisei from Eastern Africa show C₄–dominated diet, in contrast to known living and fossil hominoids, and provide a point of comparison for the Malawi Rift hominins.