Macroevolutionary Analyses of Cranial Morphology and Function in Mammals

University Of Washington, Seattle WA

Investigators

Abstract

Mammals comprise over 5,400 species, and exhibit extraordinary anatomical and dietary diversity. It is hypothesized that the great diversity of mammalian species resulted from the evolution of structures associated with an ability to access, consume and process new food resources. However, this hypothesis has not been tested for the majority of mammal groups, and therefore the question of how mammalian diversity arose remains an important, unanswered one. This project will employ a suite of modern tools in the study of anatomy and physical forces associated with feeding (such as skull or cranial anatomy, and chewing or masticatory muscles) to test this hypothesis in three of the most species-rich and ecologically diverse mammal groups: bats, carnivores and primates. The research will generate unprecedented quantitative datasets on the masticatory muscles and the three-dimensional skull anatomy of over 100 species. The researchers will explore the links between these anatomical and functional (internal) factors with external factors (such as food characteristics and diversity) as a way to understand patterns of species diversification. Through this work, the project will create a large public database of mammal 3D cranial morphology, train a diverse group of students, disseminate results through a public museum exhibit, and establish cross-disciplinary collaborations among several young investigators. Morphological and functional adaptations are important drivers of ecological diversification across the Tree of Life. Within mammals, it is hypothesized that many radiations were enabled by the evolution of morphological and functional traits that provided access to new dietary adaptive zones, but quantitative tests of this hypothesis are lacking for the broad diversity of mammals. This gap is partly rooted on the extensive lack of comparative datasets that integrate both the osteological and myological components of the feeding apparatus. These data, which currently exist for less than 2% of mammalian taxa, are critically needed both for an understanding of mammalian masticatory physiology and for the application of diversification analyses that contrast the relative influences of intrinsic versus extrinsic drivers of mammalian radiation. The proposed work will test macroevolutionary hypotheses about ecological diversification by generating the largest comparative datasets to date on the three-dimensional morphology, function and performance of the mammalian feeding apparatus. The team will couple micro-Computed Tomography, gross dissections, geometric morphometric analyses and biomechanical modeling to produce these data across three species-rich and ecologically diverse mammal clades (bats, carnivorans and primates). Phylogenetic comparative analyses will be used to test hypotheses about the influence of dietary selective regimes on the evolution of cranial morphology, function and performance, and their association with lineage diversification. The organismal aspect of the research will illuminate the biomechanics and ecomorphological diversity in mammal groups that are of broad scientific interest. This study will help elucidate the potential drivers of diversification in these groups while creating a foundation for further research on the physiology, biomechanics and evolution of mammal feeding.