Charles E Oxnard | PubMed Health

PubMed2007

Sexual dimorphism in the subadult mandible: quantification using geometric morphometrics.

There have been numerous attempts, with varying degrees of success, to differentiate males from females on the basis of the immature skeleton. We investigate here whether the mandible can discriminate immature individuals by sex; the techniques we apply are from the field of geometric morphometrics. The application of these methods in forensic anthropology is still relatively new; thus, an important aspect of this research is that it demonstrates potential applications in this discipline. The sample comprises 96 known age and sex subadult individuals; the three-dimensional coordinates of 38 landmarks are analyzed using the shape analysis software morphologika. Multivariate regressions indicated no significant sexual dimorphism in the subadult sample; this result is supported by poor cross-validated classification accuracy (59%). Our results suggest that the subadult mandible is not dimorphic (to the extent that dimorphism is not evident within the sample we studied); thus, sex determination using previously described criteria is likely to yield poor results.

Adolescent↗

PubMed2002

Craniodental variation among Macaques (Macaca), nonhuman primates.

BACKGROUND: In terms of structure and function, the skull is one of the most complicated organs in the body. It is also one of the most important parts in terms of developmental and evolutionary origins. This complexity makes it difficult to obtain evolutionary assessments if, as is usually the case with fossils, only part of the skull is available. For this reason this study involves a set of comparisons whereby the smallest functional units are studied first, and these built up, through a triple-nested hierarchical design, into more complex anatomical regions and eventually into the skull-as-a-whole. This design has been applied to macaques (Macaca) in order to reveal patterns of variation at the different levels. The profiles of such variation have been obtained both within and between species. This has lead to a search for the skull parts that have undergone similar selection pressures during evolution and comparable development patterns in both ontogeny and phylogeny. RESULTS: Morphometric analysis (Principal Components) was used to obtain these profiles of species and sex separations based on 77 cranial variables from 11 species of macaques. The results showed that 7 functional units could be aggregated into three functionally reasonable anatomical regions on the basis of similarities in profiles. These were: the masticatory apparatus containing mandible, lower teeth and upper teeth, the face as a whole combining maxilla (actually lower face) and upper face, and the cranium as a whole involving cranium and calvaria. Twenty-six variables were finally selected for analyzing the morphology of the whole skull. This last showed an overall profile similar to that revealed in the masticatory apparatus but also contained additional information pertaining to individual species and species-groups separations. CONCLUSIONS: The study provides a model for carrying out analysis of species separations and sex variation simultaneously. Through this design it seems possible to see cranio-dental elements that may result from similar developmental processes, have similar functional adaptations, and show an appropriately integrated structure morphologically. This study also implies that the biological information drawn from part of skull alone, e.g. as in studies of incomplete fossils may provide misleading information.

Animals↗

PubMedDate not supplied

Thoughts on bone biomechanics.

Simple simulations of stresses and strains in several types of localised anatomical features have been modelled using basic biomechanical thinking, experimental stress analysis employing photo-elastic methods and theoretical stress and strain analysis using a finite elements approach where the computational program utilises fast LaGrangian analysis of continua. The studies are providing results showing that, for given load proportions, the particular forms of some bones and bony architectural features seem related to stresses and strains that are relatively evenly distributed across surfaces (and therefore mechanically optimal). The results particularly show how apparently opposite (paradoxical) situations can readily occur within anatomical systems. They also provide strong biological information relevant to the assessment of such features of bone architecture in phylogenetic investigations. They even give information relevant to clinical problems.

Animals↗