Late Pliocene environmental change during the transition from Australopithecus to Homo

It has long been hypothesized that the transition from Australopithecus to Homo in eastern Africa was linked to the spread of open and arid environments near the Plio-Pleistocene boundary, but data for the latest Pliocene are scarce. Here we present new stable carbon isotope data from the late Pliocene mammalian fauna from Ledi-Geraru, in the lower Awash Valley (LAV), Ethiopia, and mammalian community analyses from the LAV and Turkana Basin. These data, combined with pedogenic carbonate stable isotopes, indicate that the two regions were largely similar through the Plio-Pleistocene, but that important environmental differences existed during the emergence of Homo around 2.8 million years ago. The mid-Pliocene to late Pliocene interval in the LAV was characterized by increasingly C₄-dominated, arid and seasonal environments. The early Homo mandible LD 350-1 has a carbon isotope value similar to that of earlier Australopithecus from the LAV, possibly indicating that the emergence of Homo from Australopithecus did not involve a dietary shift. Late Pliocene LAV environments contrast with contemporaneous environments in the Turkana Basin, which were more woody and mesic. These findings have important implications for the environmental conditions surrounding the emergence of Homo, as well as recent hypotheses regarding Plio-Pleistocene environmental change in eastern Africa.