The type specimen of Australopithecus sediba (MH1) is a late juvenile, prompting some commentators to suggest that had it lived to adulthood its morphology would have changed sufficiently so as to render hypotheses regarding its phylogenetic relations suspect. Considering the potentially critical position of this species with regard to the origins of the genus Homo, a deeper understanding of this change is especially vital. As an empirical response to this critique, a developmental simulation of the MH1 cranium was carried out using geometric morphometric techniques to extrapolate adult morphology using extant male and female chimpanzees, gorillas and humans by modelling remaining development. Multivariate comparisons of the simulated adult A. sediba crania with other early hominin taxa indicate that subsequent cranial development primarily reflects development of secondary sexual characteristics and would not likely be substantial enough to alter suggested morphological affinities of A. sediba. This study also illustrates the importance of separating developmental vectors by sex when estimating ontogenetic change. Results of the ontogenetic projections concur with those from mandible morphology, and jointly affirm the taxonomic validity of A. sediba.
Bibliographical noteFunding Information:
We thank the South African Heritage Resource agency for permits to work on the Malapa site, and the Nash family for granting access to the Malapa site and the continued support of research on their reserve. The South African Department of Science and Technology, and the African Origins Platform, the South African National Research Foundation, the Evolutionary Studies Institute, the Palaeontological Scientific Trust, the Andrew W. Mellon Foundation, the United States Diplomatic Mission to South Africa, the National Geographic Society, the A. H. Schultz Foundation, the Oppenheimer and Ackerman families, Sir Richard Branson, Sigma Xi, Texas Academy of Science, Vision 2020 Dissertation Enhancement Award of Texas A&M University, and the Program to Enhance Scholarly and Creative Activities and the International Research Travel Award Grant of Texas A&M University all provided funding for this research. D.J.d.R. holds a Liberal Arts Cornerstone Faculty Fellowship at Texas A&M University, which provided additional funding. The University of the Witwatersrand's Schools of Geosciences and Anatomical Sciences and the Evolutionary Studies Institute provided support and facilities. We thank the European Synchrotron Radiation Facility for granting beam time on ID17 for experiment #EC521. We thank E. Mbua, P. Kiura, V. Iminjili, and the National Museums of Kenya, Dr. P. Msemwa and the National Museum and House of Culture of Tanzania, S. Potze of the Ditsong Museum, B. Billings of the School of Anatomical Sciences of the University of the Witwatersrand, W. Seconna of the Iziko South African Museum, and L.M. Jellema of the Cleveland Museum of Natural History for access to comparative fossil and extant primate and human materials in their care. Numerous individuals have been involved in the ongoing preparation and excavation of these fossils including C. Dube, B. Eloff, C. Kemp, M. Kgasi, M. Languza, J. Malaza, G. Mokoma, P. Mukanela, T. Nemvhundi, M. Ngcamphalala, S. Jirah, S. Tshabalala and C. Yates. Other individuals who have given significant support to this project include B. de Klerk, C. Steininger, B. Kuhn, L. Pollarolo, B. Zipfel, J. Kretzen, D. Conforti, J. McCaffery, C. Dlamini, H. Visser, R. McCrae-Samuel, B. Nkosi, B. Louw, L. Backwell, F. Thackeray, M. Peltier, J. Soderberg and D. Roach. The A. sediba specimens are archived at the Evolutionary Studies Institute at the University of the Witwatersrand. All data used in this study are available upon request, including access to the original specimens, by bona fide scientists.
© 2016. The Author(s).
- Craniofacial morphology
- Geometric morphometrics
- Hominin evolution
- Ontogenetic projection