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Morphometrics

An essential task in the study of comparative morphology involves transforming or reducing anatomical data into numerical form. This permits an objective and replicable means by which to contrast individuals and species. Statistical treatment of morphometric data can provide tests of alternative hypotheses of taxonomy, growth and evolution.

I have used a median axis technique -- the line skeleton -- for resolving a long-standing debate on the utility of mandibular symphyseal shape as a taxonomic marker in hominoid primates. As the line skeleton essentially transforms contour data into a series of "homologous" linear and curvilinear segments, structures such as the superior transverse torus -- a region that has proven resistant to conventional caliper-driven measurement -- can be evaluated both categorically and quantitatively. Analysis of line skeletons suggests that symphysis shape does not discriminate among modern great apes. Other techniques, such as elliptical Fourier decomposition, yield similar conclusions.

Median axis methods are ideally suited for growth studies. Pictured here are line skeletons of the mandible in infant (top) and juvenile (bottom) male chimpanzees. This median axis technique allows for ontogenetic changes in different regions to be evaluated independently, and the spatial disposition of adjacent regions can be monitored throughout development. Quantifying such changes is a critical step in specifying hypotheses of  heterochronic patterns in comparative samples.

Representative Publications

Daegling, D.J. (1996) Mandibular growth in the African apes. J. Human Evol. 30: 315-341.

Daegling, D.J. (1993) Shape variation in the mandibular symphysis of apes: An application of a median axis method. Am. J. Phys. Anthropol. 91: 505-516.