Evolution and Development of Temporal Bone Pneumatization in Hominids
Open Access
- Author:
- Hill, Cheryl Ann
- Graduate Program:
- Anthropology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 28, 2008
- Committee Members:
- Joan Therese Richtsmeier, Committee Chair/Co-Chair
Alan Walker, Committee Member
Timothy Michael Ryan, Committee Member
Kenneth Monrad Weiss, Committee Member
Carol V Gay, Committee Member - Keywords:
- computed tomography
pneumatization
temporal bone
human
African apes - Abstract:
- This project investigates ontogenetic and evolutionary changes in temporal bone pneumatization, the process leading to air-filled cavities in adult temporal bones. Important conclusions regarding hominid phylogeny 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 hominid temporal bone pneumatization, as well as the developmental and functional basis for observed variation in pneumatization. This study includes three sets of analyses aimed at determining whether temporal bone pneumatization is an appropriate and informative marker for evolutionary change. First, ontogenetic changes in temporal bone pneumatization in modern humans were investigated. Second, comparative analysis of adult morphology of temporal bone pneumatization in five extant primate species was completed. Third, evolutionary changes in temporal bone pneumatization in both living and fossil Homininae species were analyzed. For the first and second studies, bone volume fractions, anisotropy, trabecular number, trabecular thickness, surface area and volume were measured in high resolution x-ray computed tomography scans acquired from adult primates and a cross-sectional ontogenetic series of humans. The third study was achieved using medical resolution scans previously acquired from fossil species, extant African apes, and modern humans. Changes in the extent of pneumatization over evolutionary and ontogenetic time are accompanied by changes in the bony material analyzed here. A number of species-specific and age-specific differences in temporal bone pneumatization were noted. The species-specific changes did not correspond to known evolutionary or morphological affinities among the species in the study. Analyses of the ontogenetic changes in pneumatization show that temporal bone pneumatization is a dynamic process that is influenced by epigenetic factors. Correct inclusion of a character in phylogenetic analyses requires that the character show consistent morphological differences among species that are minimally influenced by epigenetic factors. These results suggest that temporal bone pneumatization is not appropriate for inclusion in phylogenetic analyses, since the morphology of temporal bone pneumatization demonstrates patterning, either stochastic or of unknown origin, across species and age groups.