The application of conventional and novel morphometric techniques to problems in human evolution and ontogeny

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Abstract

This thesis is a series of case studies in the use of different morphometric techniques to answer questions in human evolution and development. It is split into two main parts. In part one, paper 1 concerns the reconstruction and body mass estimate using convex hulling, of the Australopithecine AL-288-1. The reconstruction of the rib cage using geometric morphometrics indicates that the Australopithecus afarensis rib cage and scapula may have been more human-like in small individuals such as AL288-1 than originally thought. A new reconstruction of the pelvis also demonstrates a more humanlike form, although the iliac blades are still flattened relative to other great apes. Finally, the body mass estimate of around 20.4kg using minimum convex hulling suggests that a rethink is required of models of AL288-1 that have a mass closer to 30kg. The second and third papers deal with issues sparked by the first paper. Paper 2 deals with the sexual dimorphism in body mass in a captive Pan troglodytes sample, demonstrating that captive individuals follow broadly the same trends as wild individuals, with the advantage that datasets of observations are often more densely sampled. Paper 3 deals with obstetric questions generated from the new AL288-1 pelvis reconstruction and attempt an in silico birth simulation as well as using physical reproductions for this experiment. It is demonstrated that the semi-rotational birth mechanism suggested recently is feasible, and the new reconstruction may also be able to accommodate an occiput posterior position of the head during birth. The new reconstruction is also less likely to result in a severe foetal-pelvic mismatch, which can result in catastrophic brain injuries. The second part concerns the biomechanical development of the humerus and other long bones during development. Paper 4 is a reconstruction of the Magdalenian perinate Wilczyce 1, and biomechanical analysis of the long bones indicate that this individual was extremely gracile, even when compared with medieval and post-medieval infants. Paper 5 deals with the use of "morphometric mapping" of microCT data to characterise the endostructural variation of the humerus during growth. The results confirm that a whole bone approach is more desirable than that of fixed intervals, where possible, as there is a continuous pattern of variation in both cortical thickness and circularity of the cross-section along the shaft. It is also possible to discriminate very young individuals and adolescents from other groups by relative cortical thickness, and also by periosteal surface curvature. The results were compared with Pseudo-landmarks and found to be more powerful in visualizing inter-group differences. Paper 6 extends the use of morphometric mapping to data generated by surface scanning, through the comparison of the periosteal surface contours of the humerus. Here ontogenetic samples from two agrarian groups from different climates were analysed. Analysis showed that climate had a significant effect on the datasets and both groups displayed distinct ontogenetic trajectories. The final paper uses the same suite of techniques to compare juvenile humeri of hunter-gatherers from a broadly temperate climate with farmers. Again, the two groups displayed different ontogenetic trajectories, with the hunter-gatherers appearing to have much more accelerated ontogeny. The first set of papers is expected to contribute to our understanding of extinct hominin eco-morphology; birth mechanics and size dimorphism. The second set gives more understanding of the ontogeny of the humerus in diverse human groups and possible responses to climate and activity patterns.

Keyword(s)

Anatomy; Biomechanics; MicroCT; australopithecus; bone; chimpanzee; hominins; humerus; morphometrics; onotogeny

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