Sexual dimorphism in white South African crania
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Date
2016
Authors
Small, Candice
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Abstract
Sexual dimorphism is one of four critical factors assessed by forensic anthropologists
when compiling biological profiles. The current study used geometric morphometric
methods to analyse various aspects of sexual dimorphism in white South African crania
to significantly contribute to current forensic standards for this underrepresented
population.
As edentulous crania are a major contributing factor to the low number of
publications on white South African populations, the question arose as to how tooth
loss affects cranial structures and the accuracy of sex and ancestry estimation. Two
hundred and twenty nine crania were digitised using landmarks and sliding
semilandmarks, both globally and for a number of cranial subsets. Although a number
of effects were identified when the skull was analysed globally, only the maxillary
alveolar ridges were significantly affected when subsets were analysed individually. As
both upper facial height and palate shape were significantly altered by tooth loss, the
effects of tooth loss on cranial structures and sex and ancestry estimations were
investigated.
Next, to parse out the mechanisms by which sexual dimorphism causes
morphological variation, overall sexual dimorphism, common allometry and nonallometric
sexual dimorphism were individually assessed. Global and subset data were
studied and the effects of sexual dimorphism and allometry were found to be universal,
with significant differences being observed between the sexes both globally and
regionally. A significant non-allometric component was, however, only found to
contribute to the shape of the zygomatic bone.
Finally, the accuracy of 17 widely used traditional cranial measurements was
compared to all possible interlandmark distances (ILDs) attainable from 45 fixed
landmarks. Discriminant functions derived using the ILDs compared well to those of
previous work on white South Africans, thus demonstrating the similarity between
traditional and 3-D methods. Finally, custom discriminant functions were created for a
number of cranial subsets and for the cranium in its entirety. The subsets achieved
sexing accuracies ranging between 71.8% and 83.7%, with the nasomaxilla proving
most accurate. The overall cranial function attained a cross-validated sexing accuracy
of 88.2%. These functions are critical for sex estimation not only for intact crania, but
also for the innumerable fragmentary cranial remains recovered regularly in South
Africa.
Description
Original published work submitted to the Faculty of Health Sciences, University of the
Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of
Philosophy.
Johannesburg, 2016