Masters Theses

Date of Award

12-1995

Degree Type

Thesis

Degree Name

Master of Arts

Major

Anthropology

Major Professor

Lyle W. Konigsberg

Committee Members

William M. Bass, Andrew Kramer

Abstract

Morphometry is a subfield of biometry that combines biology, geometry, and statistics for the purpose of describing biological shape and shape change to facilitate explanations of ontological and phylogenetic development. Recently morphometry has become a tool in human osteological studies to describe skeletal shapes, both in physical anthropology and in the broader areas of biomedicine. This thesis is an application of two-dimensional morphometric methods and discriminant function analysis to determine the sex of skeletal remains using the greater sciatic notch, a structure on the posterior border of the os coxa (hip bone). The sample in this study consists of 254 known sex and age os coxae from the Bass, Hamann-Todd, and Terry Collections. A black-and-white photograph was made of each sciatic notch from the ventral aspect. These photographs were scanned into the computer and digitized. The polygonal edge-approximation algorithm (Batchelor, 1980) was used to construct three homologous landmarks over the continuous form of the notch by fitting a convex hull to each digitized image. The landmarks are then scaled to the Cartesian grid, which allows the maximum width and maximum depth of the notch to be quantified. The sexual dimorphism is observed by holding two landmarks constant while allowing the other landmark to vary. The x- and y-coordinate data, or shape coordinates, are used to calculate two shape variable ratios. These variables were subjected to both linear and quadratic discriminant function analysis. The resulting linear discriminant function correctly classified 75.2% of the males, 87.2% of the females, and 81.1% of the total sample. The quadratic discriminant function correctly classified 72.9% of the males, 88.8% of the females, and 80.7% overall. These percentages illustrate that both shape variables exhibit sexual dimorphism when examined together. The male means for both shape variables are greater than in females. Males tend to have a greater length of the anterior segment of the maximum width line, and they tend to have a greater maximum depth, and these differences are reflected in the ratios produced by these shape variables. The results (percent correctly classified by the discriminant function) are compared to traditional caliper-based studies of the sciatic notch and to other discriminant function analyses elsewhere on the skeleton. The comparison revealed that morphometric methods outperformed traditional methods in sexing the notch. Because the notch is a highly variable structure, however, the current methods did not perform as well as discriminant analyses using other less variable structures. Despite these results the sciatic notch has been an excellent proving ground for the use of morphometric methods in human osteology.

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