orphology provides the set of tools that organisms use to interact with their physical environment. Most simply, morphology defines the structural basis for the ability to perform critical tasks such as procuring food and avoiding predators. With respect to the masticatory (feeding) apparatus, subtle differences in the morphology of the skull and teeth of mammals often signify adaptations to very different diets. The links between variation in morphology, feeding behavior, and feeding performance are common themes in our research.
We study the morphology of the skull and dentary using several different methods. Most simply, we apply multivariate statistical techniques to linear measurements in order to describe functional variation in the skulls and dentaries (lower jaws) of bats, marsupials, and primates. These measurements not only reflect the size and shape, but also the lever and load arms associated with static mechanical models of masticatory function. These data have allowed us to answer questions like, do morphological correlates of dietary adaptation cut across taxonomic groups? And, do ecologically convergent assemblages of mammals exhibit similar patterns of morphological diversity? We also use modern comparative techniques (independent contrasts and squared change parsimony) to evaluate the correlated evolution of different parts of the craniofacial skeleton as well as correlations between morphology and the evolution of specific dietary adaptations. For example, in a sample of bats we have identified a suite of morphological traits that are significantly associated with the evolution of hard-object feeding in small-bodied species.
Documenting bone cross-sectional properties and volumes of intra-cranial structures from serial sections is a more complex morphometric technique that we use. To date, we have collected serial sections of the entire skull and cross-sections of the dentaries for ## species. We use these data to investigate questions including, are dietary adaptations reflected in the cross-sectional geometry of the dentary?, how does nasal cavity volume scale with skull size?, and, how does the internal morphology of the nasal cavity vary among bats? Our collection of raw serial scans of bat skulls can be downloaded as NIH Image stacks. We invite you to use these resources in your research and welcome your feedback.
Other ongoing morphometric projects include investigations of the evolution of tubular nostrils and sexual dimorphism in Old World fruit bats, documenting patterns of tooth sharpness along the tooth row, and assessing the relative timing of evolutionary changes in wing structure and the evolution of dietary adaptations among the New World leaf-nosed bats. We are also collaborating with Dr. Ian Grosse to develop detailed finite element models of bat skulls that will be used to test functional hypothesis concerning the evolution of variation in craniofacial form.
