GOSWAMI, A; University of Chicago, IL and Field Museum, Chicago, IL: Morphological Integration in the Mammalian Skull: The Influences of Phylogeny, Function, and Ontogeny

Recent genetic and developmental studies have produced compelling hypotheses of the importance of trait correlations to morphological evolution. However, these hypotheses have never been tested with a broad, comparative data set or with fossil material. This study uses the analysis of morphological integration to examine discrete sets of highly correlated cranial traits and their relationship to factors influencing mammalian skull evolution. Here, I present detailed analyses of patterns of cranial trait correlations across a broad range of taxa within the terrestrial Carnivora, Primates, and Marsupialia, addressing the relationship of these patterns to phylogeny, ontogeny, and function. A 3D digitizer was used to record 60 homologous skull landmarks from approximately 20 specimens of ~100 extant species and 15-20 fossil species. The inclusion of fossil taxa expands phylogenetic breadth and permits testing of temporal trends in skull modularity and the influence of increased brain size within lineages. Matrix correlation analysis supports a loose relationship between phylogeny and patterns of trait correlation, though these patterns are not generally conserved across mammals. Brain size and convergence of diet are explored as alternative or additional influences on cranial integration. I also present a new method for comparing independent data sets and summarizing patterns of trait correlations, derived from principal components analysis. Rather than assuming a common principal component structure, our method compares the ordering of eigenvectors and the angle between matched eigenvectors among multiple covariance matrices, generating a measure of similarity more appropriate for comparing trait correlations.