Abstract
Comparative biomolecular studies suggest that the last common ancestor of humans and chimpanzees, our closest living relatives, lived during the Late Miocene–Early Pliocene1,2. Fossil evidence of Late Miocene–Early Pliocene hominid evolution is rare and limited to a few sites in Ethiopia3,4,5, Kenya6 and Chad7. Here we report new Early Pliocene hominid discoveries and their palaeoenvironmental context from the fossiliferous deposits of As Duma, Gona Western Margin (GWM), Afar, Ethiopia. The hominid dental anatomy (occlusal enamel thickness, absolute and relative size of the first and second lower molar crowns, and premolar crown and radicular anatomy) indicates attribution to Ardipithecus ramidus. The combined radioisotopic and palaeomagnetic data suggest an age of between 4.51 and 4.32 million years for the hominid finds at As Duma. Diverse sources of data (sedimentology, faunal composition, ecomorphological variables and stable carbon isotopic evidence from the palaeosols and fossil tooth enamel) indicate that the Early Pliocene As Duma sediments sample a moderate rainfall woodland and woodland/grassland.
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Acknowledgements
The L.S.B. Leakey Foundation provided a major grant for the Gona Project, and the National Science Foundation (and Researching Hominid Origins Initiative-RHOI), the Wenner-Gren Foundation and the National Geographic Society funded the research. We thank N. Toth and K. Schick (co-directors of CRAFT Stone Age Institute, Indiana University) for their overall assistance. S.S. thanks N. Toth and K. Schick, and Friends of CRAFT for the Research Associate position at the Institute. The research permission by the Ministry of Youth, Sports and Culture, the Authority for Research and Conservation of Cultural Heritage and the National Museum of Ethiopia is greatly appreciated. We thank the Afar Regional Administration and the Afar colleagues at Eloha and Asayta for their hospitality, and A. Humet for the hard work in the field. Y. Beyene, C. Howell, B. Lasher and A. Almquist encouraged the research. D. Stout, L. Harlacker, M. Everett and T. Pickering assisted in the field, and A. Tamburro at CRAFT. The manuscript has benefited from discussions with B. Asfaw, M. Asnake, R. E. Bernor, J.-R. Boisserie, M. Brunet, S. Frost, Y. Haile-Selassie, O. Lovejoy, M. Pickford, E. Smith, H. Wesselman and T. White. M. Sahnouni and B. Smith helped with computer graphics.
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Supplementary information
Supplementary Table S1
Supplementary Table 1 provides preliminary identification of fauna collected from the Early Pliocene hominid-bearing deposits from As Duma, Gona Project Area, Ethiopia. (DOC 27 kb)
Supplementary Table S2
This contains argon isotope data for plagioclase crystals from tuffs GONASH-51 and GONASH-52, which provides the basis for the age data depicted in Supplementary Figures S1 and S2. (DOC 92 kb)
Supplementary Table S3
This contains the complete 40Ar/39Ar analytical data obtained from two basalt flows (WM-25 and WM-27) from the Western Margin samples at Gona. Results for individual groundmass concentrate subsamples, along with the integrated and plateau ages for the two basalt flows are presented. (DOC 158 kb)
Supplementary Table S4
This contains a list of all the samples of soil carbonate collected in the Gona project from the Gona Western Margin, the carbon isotope (expressed as δ13C VPDB) values for each sample and the average δ13C value in each paleosol pooled from individual results. (DOC 117 kb)
Supplementary Table S5
This contains a list of all the samples of fossil tooth enamel collected in the Gona project from the Gona Western Margin, the tooth element and animal species analysed and the carbon isotope (expressed as δ13C VPDB) value for each sample. (DOC 103 kb)
Supplementary Figure S1
Age-probability diagram for Run 31200, Sample G-51. This summarizes the results of 40Ar/39Ar age determinations and compositional data of individual palgoioclase crystals from tuff GONASH-51. (GIF 45 kb)
Supplementary Figure S2
Age-probability diagram for Run 31202, Sample G-52. This summarizes the results of 40Ar/39Ar age determinations and compositional data of individual palgoioclase crystals from tuffs GONASH-52. (GIF 48 kb)
Supplementary Figure S3
This shows age spectrum and isotope correlation diagram for Run 52560, Sample WMASH-25, groundmass concentrate. (GIF 80 kb)
Supplementary Figure S4
This displays age spectrum and isotope correlation diagram for Run 552558-01, Sample WMASH-27, groundmass concentrate. (GIF 81 kb)
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Semaw, S., Simpson, S., Quade, J. et al. Early Pliocene hominids from Gona, Ethiopia. Nature 433, 301–305 (2005). https://doi.org/10.1038/nature03177
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DOI: https://doi.org/10.1038/nature03177
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