1Human Evolutionary Biology, Harvard University, 2X-ray Imaging Group, European Synchrotron Radiation Facility
Friday All day, Park Concourse
Seasonal climatic patterns may have influenced the evolution of human foraging behaviors and tool use during the Plio-Pleistocene. One means of reconstructing climatic parameters is through sequentially sampling stable light isotopes from fossil dentitions. However this method requires knowledge of the pattern of mineral deposition within developing teeth, which is poorly understood. Here we use micro-computed tomography (uCT) to assess temporal and spatial patterns of mineral deposition in 25 developing molar crowns of domesticated sheep (Ovis aries) aged 0-32 weeks. Mineral densities are quantitatively measured using hydroxyapatite standards manufactured for this study. Comparisons of successive age classes reveals that the rates of cellular activation (extension) and maturation phases of mineral deposition are distinct, with maturation at first lagging behind but ultimately advancing more rapidly than activation. Extension rates are comparable to published rates determined from histological study. Importantly, the geometry of maturation is found to be different than that of activation and secretion. Controlled 3-dimensional planes reveal how different sequential sampling strategies integrate different periods of time during tooth formation. Furthermore, we show how optimization of anode choice and beam power, flux, and filtering improves quantification of density. While synchrotron microtomography holds greater potential for quantitative reconstruction of densities, both uCT and synchrotron imaging are powerful tools for revealing mineralization processes. Ultimately, an improved understanding of mineralization will inform sampling procedures for reconstructing seasonal processes, and contribute to our understanding of the climatic context of human origins and evolution.
Funded by Harvard University, the European Synchrotron Radiation Facility, and the National Science Foundation.