Doctoral Dissertation Improvement: Quantitative Analysis of Temporal Bone Pneumatization in Homininae

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This project will investigate evolutionary and growth-related changes in temporal bone pneumatization, the widespread process leading to air-filled cavities in adult temporal bones. Important conclusions regarding hominin phylogeny and craniofacial evolution have included temporal bone pneumatization as a phylogenetic, or species-specific, marker. Despite its previous inclusion in evolutionary analyses, a number of questions remain concerning the evolutionary and developmental changes in Homininae temporal bone pneumatization, as well as the developmental and functional basis for observed variation in pneumatization. The correct inclusion of this character in studies of human evolution requires a thorough understanding of the development and cause of temporal bone pneumatization, especially in correlation with other important traits showing evolutionary change. The proposed study will complete three objectives to determine if temporal bone pneumatization is an appropriate and informative marker for evolutionary change. First, a comparative analysis of adult morphology of temporal bone pneumatization in four living African ape and human species will be completed. Second, growth-related changes in temporal bone pneumatization in modern humans will be investigated. Third, evolutionary changes in temporal bone pneumatization in both living and fossil Homininae species will be analyzed. For the first and second objectives, a number of parameters, such as surface area, bone volume fraction, and anisotropy, or bone directionality, will be measured in high resolution computed tomography scans acquired from adult individuals and a cross-sectional growth series of humans. The third objective will be completed using low resolution scans previously acquired from fossil species, extant African apes, and modern humans. The proposed analyses will provide unique and important information about growth-related and evolutionary changes in temporal bone pneumatization in Homininae, and investigate potential correlations between temporal bone pneumatization and well-defined evolutionary changes in the skull, such as basicranial flexion and increased brain size. The proposed study will develop a novel approach for quantitatively analyzing pneumatization in Homininae skulls. This approach holds great promise for the quantitative assessment of pneumatized spaces in vertebrate skulls. High resolution computed tomography scans acquired during the course of the study will be distributed to the larger scientific community through the establishment of an image archive, encouraging collaborative work among scientists studying the temporal bone, the ear, and pneumatization. Aspects of the temporal bone not investigated here, e.g., physiology, hearing and balance, can be studied using these images. This study will also encourage collaboration and interaction between anthropological and biomedical researchers, as pneumatization is an important aspect of functional morphology and temporal bone physiology for both fields. Finally, this project will advance the education and training of a graduate student in preparation for a strong, independent research career.