Stable isotope dietary reconstructions of herbivore enamel reveal heterogeneous savanna ecosystems in the Plio-Pleistocene Malawi Rift

The Plio-Pleistocene expansion of Eastern Africa savanna ecosystems was a major driver for morphological and behavioral innovations in hominin evolution. Most evidence for hominin ecosystem reconstructions originates from the Eastern Rift in today's Somali-Masai Endemic Zone. We provide stable carbon (δ 13 C) and oxygen (δ 18 O) isotope data from 22 bovid, equid, suid, hippopotamid and elephant teeth from the southern part of the East African Rift and supplement these by δ 18 O values of present-day meteoric water. This region (Karonga Basin, Malawi) hosts remains of Homo rudolfensis and Paranthropus boisei . It is situated between hominin-bearing sites in Eastern and Southern Africa and therefore fills an important geographical gap for hominin evolution. Tooth enamel δ 13 C and δ 18 O data of 14 large-bodied mammalian herbivore species from Units 2 and 3 (ca. 4.3 to 0.6 Ma) in the Chiwondo Beds provide information about foraging strategies and vegetation patterns. Our stable isotope data reflect C 3 -dominated ecosystems that permitted access to open C 4 -environments for migratory mammals. Many analyzed taxa show evidence for mixed diets with high abundances of C 3 -biomass consumption; only selected bovids were specialized grazers. δ 18 O of present-day meteoric water reflects rainfall amount and seasonality, elevation, and lake evaporation. δ 18 O values of Karonga Basin herbivore enamel are generally low and cover values similar to present-day drinking water, indicating both, evaporated and freshwater sources. Comparison of δ 13 C values from the Karonga Basin with other Eastern African herbivore communities reveals significant differences in dietary patterns with much more generalized mixed C 3 /C 4 , and pure C 3 feeding behaviors in the Malawi Rift. Similarly, enamel δ 18 O values are lower than in most Plio-Pleistocene Eastern African herbivores, suggesting more humid conditions. Collectively, our data support models in which early hominin foraging activity included access to C 3 -dominated biomes, complicating traditional interpretations linking early human evolutionary innovations to a shift towards savanna habitats.