The environment of the Ethiopian highlands at the mid Pleistocene transition. Fauna, flora and hominins in the 850-700ka sequence of Gombore II (Melka Kunture)

Environment, climatic change and human evolution have been debated over the last 50 years giving special attention to the Plio-Pleistocene sites of the Rift Valley. In this paper we discuss the environment and the limits of hominin adaptability based on evidence from Melka Kunture, at 2000 m asl on the Ethiopian highlands, and specifically on the ~850 ka to ~700 ka sequence at sub-site Gombore II. Human fossils and multiple Acheulean occurrences, as well as hippo remains and footprints, combined with palynological analysis, provide a highly detailed chronological resolution of the changing local environmental conditions during the last ~150 ka of the MPT (Mid Pleistocene Transition), including the sequence of events after a volcanic eruption. Layers containing footprints and fossils are evidence of near-continuous occupation by hippos and their recolonization of the area after a disruptive volcanic eruption. Conversely, Acheulean implements and human fossils suggest that peopling by hominins occurred at a different and discontinuous pace even when the flora and fauna were re-established and the environment was rather stable. Most notably, the assembled evidence points to the limits of Homo erectus s.l. adaptability. Apparently, this hominin could no longer live at 2000 m asl when the climate deteriorated during glacial isotopic stage 20, becoming markedly colder than it is today, but re-colonized the area when the climate turned warmer again during isotopic stage 19.