Late Pliocene environmental change during the transition from Australopithecus to Homo

Abstract

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.

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Figure 1: Box-and-whisker plots of mammalian enamel δ13C values.
Figure 2: Correspondence analysis of mammal community functional traits for fossil communities from the lower Awash Valley and the Turkana Basin.
Figure 3: Compilation of the available δ13C values of tooth enamel from the LGRP area, the Hadar Formation, and the Nachukui and Koobi Fora formations in the Turkana Basin spanning the interval of around 3.5 to 1.0 Ma.

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Acknowledgements

We thank the curators and staff of the Authority for Research and Conservation of Cultural Heritage at the Ethiopian National Museum in Addis Ababa, Ethiopia, for access to fossil specimens in their care. We thank the Afar people for assisting with fieldwork. Thanks to J. Wilson for helping to analyse samples at the University of South Florida. We thank M. Leakey for access to the most recent version of the Turkana Database. J.R. was supported by a National Science Foundation Graduate Research Fellowship. Field and lab work in the Ledi-Geraru area was made possible by National Science Foundation grant BCS-1157351. This research was also made possible through the support of a grant from the John Templeton Foundation to the Institute of Human Origins at Arizona State University. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation.

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J.R.R., J.R., C.J.C., J.G.W. and K.E.R. designed and performed the research, analysed the data and wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Joshua R. Robinson.

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Supplementary information

Supplementary Information

Supplementary Methods, Supplementary Discussion of the carbon and oxygen isotope results, Supplementary Figures, Supplementary Tables, and Supplementary References (PDF 3049 kb)

Supplementary Data 1

Raw values and catalogue numbers for all individual teeth included in this study. Taxonomic identifications and detailed descriptions for each tooth sampled are also included. (XLSX 22 kb)

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Robinson, J., Rowan, J., Campisano, C. et al. Late Pliocene environmental change during the transition from Australopithecus to Homo. Nat Ecol Evol 1, 0159 (2017). https://doi.org/10.1038/s41559-017-0159

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