Understanding the origin of modern communities is a fundamental goal of ecology, but reconstructing the history of communities that include species with stratigraphic durations on the scale of hundreds of thousands to millions of years necessarily requires data from the fossil record. Similarly, inferences about the paleoecology of past communities are most robust when informed by data from both living and fossil populations of extant species. Despite the logical connections between ecology and paleoecology, relatively few studies have bridged the gaps in the characteristic observational timescales and methodologies of these disciplines to achieve a comprehensive view of the long-term evolution of specific modern communities. The need to bridge these disciplinary gaps is increasingly pressing in the face of anthropogenic climate change and uncertainty about the magnitude and direction of responses by local communities. This large collaborative project examines the ecological, environmental, and climatic context of the origin of the modern small mammal community in the grasslands of the central USA over the last five million years. We are testing the effects of both biological and non-biological factors on long-term taxonomic turnover and ecological change in a stratigraphic sequence of local communities using a combination of ecomorphology, biogeochemistry, paleoclimate modeling, and biogeography. Our results so far are consistent with a surprisingly small role for climate or habitat changes in structuring faunal changes, suggesting that biological interactions among small mammal species may be more important.