Understanding changes in ontogenetic development is central to the study of human evolution. With the exception of Neanderthals, the growth patterns of fossil hominins have not been studied comprehensively because the fossil record currently lacks specimens that document both cranial and postcranial development at young ontogenetic stages. Here we describe a well-preserved 3.3-million-year-old juvenile partial skeleton of Australopithecus afarensis discovered in the Dikika research area of Ethiopia. The skull of the approximately three-year-old presumed female shows that most features diagnostic of the species are evident even at this early stage of development. The find includes many previously unknown skeletal elements from the Pliocene hominin record, including a hyoid bone that has a typical African ape morphology. The foot and other evidence from the lower limb provide clear evidence for bipedal locomotion, but the gorilla-like scapula and long and curved manual phalanges raise new questions about the importance of arboreal behaviour in the A. afarensis locomotor repertoire.
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We thank the Authority for Research and Conservation of Cultural Heritage (ARCCH) and the National Museum of Ethiopia of the Ministry of Tourism and Culture, and the Afar regional government for permits; A. Dessie, T. Gebreselassie, G. Assefa, A. Kebede, M. Mekonnen, H. Defar, A. Zerihun, A. Takele and the people of the Dikika area for field assistance; A. Admassu for laboratory assistance; the National Geographic Society, the Institute of Human Origins at ASU and the Leakey Foundation for financial and logistical support. For discussions and help, we thank R. Ackermann, M. Clegg, H. Coqueugniot, C. Dean, T. Fitch, J.-J. Hublin, L. Humphrey, P. Jenkins, D. Johanson, K. Kupczik, S. Larson, D. Lieberman, C. Lockwood, R. Martin, E. Mbua, R. McCarthy, K. Mowbray, P. Morris, T. Nishimura, P. O'Higgins, O. Pearson, A. Pommert, Y. Rak, J. Richtsmeier, L. Scheuer, B. Sokhi, B. Viola, C. Ward and T. Weaver. We also thank B. Wood for critical comments and suggestions that have improved our paper greatly.
This file contains seven sections of Supplementary Notes. S1 details dental dimensions and sex of DIK-1-1. S2 details the facial profile. S3 discusses brain EV estimates. S4 discusses brain EV growth (absolute, relative). S5 describes the Hyoid, S6 the scapula and S7 details the semicircular canal size (absolute, relative). This file also contains additional references.