Developmental Simulation of the Adult Cranial Morphology of Australopithecus sediba
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The present study involves the developmental simulation of the adult cranial morphology of the newly discovered species, Australopithecus sediba. Au. sediba has been the focus of considerable discussion and debate in paleoanthropology, following its announcement as a new species in 2010. The unique mosaic morphology of the Malapa hominins - with features aligning them to both earlier species of australopith as well as later Homo - has led some to hypothesize that Au. sediba represents the best candidate ancestor to the genus Homo. To date, only a single, relatively complete cranium has been recovered from the Malapa fossil site, belonging to the type specimen designated MH1. While its second molars are erupted and in occlusion, the third molars remain in the crypt, indicating the juvenile status of MH1. Some commentators have suggested that, because MH1 was a juvenile, its morphology may have changed substantially as it progressed towards adulthood. Further, these changes may have been significant enough to alter current interpretations of its morphological affinities, including traits thought to align Au. sediba with the genus Homo. As such, understanding the degree and nature of change to be expected to occur between second and third molar eruption is of crucial importance. The present study has addressed this problem using 3D geometric morphometric techniques for the developmental simulation of the MH1 fossil cranium. Landmark-based developmental vectors were acquired from three extant hominoid species, including chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), and modern humans (H. sapiens). Vectors were separated by sex to control for the influence of secondary sexual characteristics and applied to the reconstructed MH1 cranium. Six virtual adult crania were generated in total, a male and female from each of the three extant hominoid species used in simulation. In order to understand the morphological affinities of these generated adults in a broader comparative context, multivariate tests were carried out using a sample of non-robust hominin crania. The results indicate that the majority of morphological changes expected to occur between second and third molar eruption are related to puberty. Results acquired from principal components analysis (PCA) and Procrustes distance matrix analysis indicate that all simulated adult crania of Au. sediba show greater similarities to one another than to other hominin species. All simulated Au. sediba adults consistently clustered together with the original juvenile cranium in PCA, separate from other hominin taxa. Results acquired from distance matrices also indicate that variation within the sample of simulated adult Au. sediba crania does not exceed that of other extant hominoid species, regardless of the developmental vector applied. Therefore, the results of this study provide empirical support for a separate, species-level diagnosis for Au. sediba, and further indicate the need to account for sexual dimorphism in morphometric studies of developmental simulation.
Carlson, Keely Britt (2014). Developmental Simulation of the Adult Cranial Morphology of Australopithecus sediba. Doctoral dissertation, Texas A & M University. Available electronically from