Paleoenvironmental change in the late Middle Pleistocene-Holocene Kibish Formation, southern Ethiopia: Evidence from ungulate isotopic ecology

摘要

East Africa has produced the earliest record of Homo sapiens similar to 200 ka and a punctuated record of Middle Stone Age and Later Stone Age behaviors. We lack, however, a detailed late Quaternary paleoenvironmental record for the region, particularly during humid periods. Without a regional record, hypotheses about the evolution and ecology of early Homo sapiens in East Africa remain vague and untestable. The Kibish Formation of southern Ethiopia presents a long, albeit punctuated, record of late Middle Pleistocene to Holocene faunal change in East Africa, which was deposited during humid periods. Here, we present oxygen and carbon stable isotope data of the Kibish ungulates and test whether there are environmental changes within the Kibish Formation. Significant differences in delta O-18 enamel isotopes are consistent with more humid conditions during the Holocene-age Member IV (similar to 13-4 ka) than either Pleistocene-age Member I (similar to 196 ka) or Member III (similar to 104 ka). Mesowear data document a shift toward more attritional wear among grazers in Member IV and are correlated with more depleted delta O-18 enamel values, suggesting that the wear pattern shift is linked to the onset of more humid conditions during the Holocene. delta C-13 enamel values show subtle variations through time, but do not suggest any major changes in diets. We propose that the paleoenvironmental differences evident in Member IV, based on delta O-18 enamel values, mesowear, and bovid abundances, may be explained by cooler and wetter conditions at the beginning of the Holocene in the lower Omo Valley. The evidence suggesting that the Holocene humid phase is more pronounced than earlier humid phases may explain why arid-adapted grassland ungulates became extinct in East Africa by the Pleistocene-Holocene transition, but persisted through previous humid phases of the late Quaternary. (C) 2016 Elsevier B.V. All rights reserved.