GOSWAMI, A; Univ. of Chicago, IL and The Field Museum, Chicago, IL: Morphometric analysis of higher-taxonomic-level variation in cranial modularity across mammals

The correlated evolution of traits is a principal factor in morphological evolution, but it is typically studied in genetic or developmental systems. The concept of modules (genetically, developmentally, and morphologically integrated subsets of traits within more traditional units) is an ideal bridge between these disparate scales of evolutionary analysis. Here, I examine phenotypic modularity, via morphometric analysis, in 85 mammalian species from the placental orders Carnivora and Primates and the marsupial orders Dasyuromorphia, Peramelia, and Diprodontia, spanning a wide range of ecological and morphological diversity. 55-60 cranial landmarks were captured through 3D digitization for 15-22 specimens per species. Cluster analyses of trait covariances for each taxon revealed a high degree of variability in cranial modules. Modules of the facial region display strong within-group correlations and are invariant in trait associations across most mammals. Molar traits and anterior oral-nasal traits form distinct groups in most marsupials and carnivorans, but not in most primates. Modules of the neurocranial region are more variable in trait associations, even within families. The orbit and zygomatic/anterior-cranial-base are particularly variable, potentially reflecting the developmental complexity of that region, while the posterior cranial base is highly integrated in all mammals. The cranial vault is highly integrated only in felids (except Smilodon) and a few marsupials. While marsupials and carnivorans do not differ significantly in within-module correlations, primates show significantly lower correlations than carnivorans and marsupials in most modules, most notably in the cranial vault.