Woody cover and hominin environments in the past 6 million years

Abstract

The role of African savannahs in the evolution of early hominins has been debated for nearly a century. Resolution of this issue has been hindered by difficulty in quantifying the fraction of woody cover in the fossil record. Here we show that the fraction of woody cover in tropical ecosystems can be quantified using stable carbon isotopes in soils. Furthermore, we use fossil soils from hominin sites in the Awash and Omo-Turkana basins in eastern Africa to reconstruct the fraction of woody cover since the Late Miocene epoch (about 7 million years ago). 13C/12C ratio data from 1,300 palaeosols at or adjacent to hominin sites dating to at least 6 million years ago show that woody cover was predominantly less than 40% at most sites. These data point to the prevalence of open environments at the majority of hominin fossil sites in eastern Africa over the past 6 million years.

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Figure 1: Correlation of δ 13 C between gap and canopy samples for 76 tropical soils used in this study.
Figure 2: Woody cover and soil δ 13 C for 76 tropical soils used in this study.
Figure 3: Surface soil temperatures from soil temperature profiles.
Figure 4: Estimated fraction of woody cover based on >1,300 published analyses of palaeosols from eastern African hominin sites from 6 Myr ago to present25,26,29,30,31,46,47,48,49,50.
Figure 5: Map with modern soil sites and hominin-fossil bearing localities in the East African Rift System overlain on GTOPO30 digital elevation model.
Figure 6: Composite record of palaeosol stable isotopic composition from the Awash Valley, Ethiopia (left) and Omo-Turkana Basin, Kenya and Ethiopia (right).

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Acknowledgements

We thank the governments of Kenya and Ethiopia for permission to conduct this research, and F. H. Brown for discussions. The authors thank Kenya Wildlife Service and members of the Dikika and Gona Research Projects for support in the field, and Z. Bedaso for aid with analyses. This research was supported by funding from the LSB Leakey Foundation and NSF grants BCS 0621542, EAR-0617010, EAR-0937819 and BCS-0321893.

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S.A.A., M.I.B., T.E.C., D.K.K., N.E.L., W.M., J.Q. and C.H.R. designed the modern soil surveys. T.E.C., M.I.B., A.N.M., W.M. and J.G.W. evaluated the amount of woody cover. C.H.R. and W.M. analysed the soil temperature data. M.I.B., N.E.L., A.N.M. and J.G.W. analysed modern soils. N.E.L., J.Q. and J.G.W. contributed new palaeosol data. T.E.C. and J.G.W. wrote the paper with input from all authors.

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Correspondence to Thure E. Cerling.

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Cerling, T., Wynn, J., Andanje, S. et al. Woody cover and hominin environments in the past 6 million years. Nature 476, 51–56 (2011). https://doi.org/10.1038/nature10306

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