MORPHOMETRICS OF THE CALLITRICHID FORELIMB - A CASE-STUDY IN SIZE ANDSHAPE

Mosimann and colleagues formulated a technique that distinguishes betw een size and shape, based on the concept of geometric similarity and t he distinction between ''log size-and-shape'' and ''log shape'' variab les. We extend these formulations in an examination of the forelimb of three callitrichid species (adult Saguinus oedipus, Saguinus fuscicol lis, and Callithrix jacchus). We employ principal components analysis to explore the relationship between variance explained by size-and-sha pe versus shape alone. Independence of shape vectors is examined via c orrelation analysis. Then we use log shape data to construct intersamp le (species means) and total sample (between all pairs of individuals) matrices of average taxonomic distances. These distance matrices are subjected to cluster analysis and principal coordinate ordinations. Re sults of principal components analysis suggest that after isometric si ze is removed, there remains sufficient shape information to discrimin ate among the three taw. Careful examination and quantification of the relationships between shape and size suggest that size information (e g., geometric mean) is fundamental for understanding shape differences within and among callitrichid species; in other words, most aspects o f forelimb shape are significantly correlated with size. Contrary to c onventional wisdom, we also demonstrate that such correlations are not ''spurious.'' Ordinations and clustering of log shape distance matric es (based on means and individuals) support the notion that, despite d ifferences in size, the two tamarins are more similar in shape than ei ther is to C. jacchus (despite size similarity between S. fuscicollis and C.jacchus). Although shape variation in the forelimb of callitrich ids may have a functional component, the phylogenetic signal remains s trong and serves to group individuals accordingly.