Asa Issie, Aramis and the origin of Australopithecus

Abstract

The origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central problem in human evolutionary studies. Australopithecus species differ markedly from extant African apes and candidate ancestral hominids such as Ardipithecus, Orrorin and Sahelanthropus. The earliest described Australopithecus species is Au. anamensis, the probable chronospecies ancestor of Au. afarensis. Here we describe newly discovered fossils from the Middle Awash study area that extend the known Au. anamensis range into northeastern Ethiopia. The new fossils are from chronometrically controlled stratigraphic sequences and date to about 4.1–4.2 million years ago. They include diagnostic craniodental remains, the largest hominid canine yet recovered, and the earliest Australopithecus femur. These new fossils are sampled from a woodland context. Temporal and anatomical intermediacy between Ar. ramidus and Au. afarensis suggest a relatively rapid shift from Ardipithecus to Australopithecus in this region of Africa, involving either replacement or accelerated phyletic evolution.

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Figure 1: Geography, stratigraphy, chronology and faunal background for the Asa Issie hominids.
Figure 2: Aramis and Asa Issie fossil hominids.
Figure 3: Dental features of the Asa Issie hominid dentition.
Figure 4: Phylogenetic hypotheses.

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Acknowledgements

We thank the National Science Foundation (including the Revealing Hominid Origins Initiative/HOMINID program), the Institute of Geophysics and Planetary Physics of the University of California at Los Alamos National Laboratory (LANL), the Japan Society for the Promotion of Science, the Fondation Singer-Polignac, and the Philip and Elaina Hampton Fund for Faculty International Initiatives at Miami University for financial support of field and laboratory research. The Earth and Environmental Sciences Division Electron Microprobe laboratory at LANL assisted with access and use. We thank A. Ademassu, W. Amerga, A. Amzaye, A. Asfaw, G. Assefa, F. Bibi, M. Black, D. Brill, K. Brudvik, M. Chalachew, M. Chubachi, W. Demisse (in memoriam), N. Eldredge, H. Elema, E. Güleç, M. Haydera, R. Jabbour, A.-R. Jaouni, K. Kairento, F. Kaya, K. Kimeu, B. Kyongo, D. Kubo, W. Liu, S. Mahieu, W. Mangao, M. McCollum, E. Mekonnen, W. Mihel, L. Morgan, C. Pehlevan, P. Reno, G. Richards, B. Rosenman, M. Serrat, A. Shabel, L. Smeenk, B. Tegengne, A. Terrazas and S. Yoseph for fieldwork, laboratory work and discussion, and M. Leakey for collections access. We thank the Ministry of Youth, Sports and Culture, the Authority for Research and Conservation of the Cultural Heritage, and the National Museum of Ethiopia for permissions and facilitation. We also thank the Afar Regional Government, the Afar people of the Middle Awash, and many others for contributing directly to the research efforts.

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Supplementary information

Supplementary Discussion 1

Dental metric comparisons. (PDF 734 kb)

Supplementary Discussion 2

Enamel thickness measurements. (PDF 47 kb)

Supplementary Discussion 3

Cladistic relationships. (PDF 652 kb)

Supplementary Figure 1

ASI paleosol carbonates. (PDF 154 kb)

Supplementary Figure 2

Comparative dental morphology. (PDF 1062 kb)

Supplementary Figure 3

Argon-argon results. (PDF 131 kb)

Supplementary Table 1

Hominid fossils. (PDF 42 kb)

Supplementary Table 2

Isotopic composition of paleosol carbonates. (PDF 21 kb)

Supplementary Table 3

Faunal list. (PDF 52 kb)

Supplementary Table 4

Radioisotopic dating results. (PDF 30 kb)

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White, T., WoldeGabriel, G., Asfaw, B. et al. Asa Issie, Aramis and the origin of Australopithecus. Nature 440, 883–889 (2006). https://doi.org/10.1038/nature04629

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