Finite-element scaling applied to sexual dimorphism in rhesus macaque (Macaca mulatta) facial growth

While many advances have been made in the statistical treatment of morphometrics, there has been little improvement in the design of measurements subjected to statistical analysis. Commonly measured linear dimensions result in a loss of geometrical integrity and an inability to translate multivariate statistical results into material three-dimensional morphology. Problems with the definition of size and shape, spurious correlation, and anatomical localization of form change or difference arise with linear dimensions. Finite-element scaling methods overcome these problems and produce measures that can be subjected to standard multivariate statistical analyses. The finite-element scaling method is described, as are measures of local and general size and shape change. We use finite-element scaling as a basis for an analysis of sexual dimorphism in rhesus macaque (Macaca mulatto) facial growth. Males grow approximately twice as fast as females, although facial growth stops at nearly the same age in the two sexes. The adult female face is morphologically quite similar in all aspects of size and shape to that of a juvenile male (4.5 years old). Thus, considered heterochronically, and taking the female morphology as primitive, sexual dimorphism in the size and shape of the rhesus face arose through rate hypermorphosis. Growth of the face was strongly allometric, with the maxillary alveolus growing much faster than other facial regions. Finite-element scaling is a very useful measurement tool for the comparison of forms, especially in studies of growth and phylogenetic transformation. [Finite-element scaling; Macaca mulatta; rhesus macaque; sexual dimorphism; facial growth.].