We develop a method to evaluate the degree to which particular morphological characteristics contribute to multivariate group differences in general and to secondary sexual dimorphism for size and shape in particular. In addition, we recommend a correlative approach to assess the degree to which the contribution of characters to group differences is consistent in different taxa. We apply both methods to a suite of 12 cranial characters obtained from populations of 18 species of bats in five families (Emballonuridae, Noctilionidae, Phyllostomidae, Vespertilionidae, and Molossidae) from Caatinga and edaphic Cerrado biomes of northeastern Brazil. As expected, a correlation usually does not exist between profiles of the importance of characters to sexual dimorphism from the two biomes if the taxa are monomorphic with regard to sex (e.g., Vampyrops lineatus, Artibeus lituratus, and Myotis riparia); any differences between the sexes within a biome are a result of chance. In contrast, significant correlations between profiles of importance of characters to intersexual variation in the two biomes usually exist when species are dimorphic (e.g., Anoura geoffroyi, Carollia perspicillata, Glossophaga soricina, Phyllostomus discolor, Molossus molossus, and Artibeus planirostris). Significant constraints on the expression of sexual dimorphism exist between populations of the same species; similar suites of characters are involved in intersexual variation if dimorphism exists. Such constraints appear inoperative at higher taxonomic levels. We hypothesize that once differentiation occurs at the specific level, coadapted gene complexes and genetic dynamics associated with epistasis, pleiomorphism, and linkage disequilibrium no longer constrain dimorphism in the same fashion as in the ancestral condition.