Unique functional diversity during early Cenozoic mammal radiation of North America

Mammals influence nearly all aspects of energy flow and habitat structure in modern terrestrial ecosystems. However, anthropogenic effects likely have altered mammalian community structure, raising the question of how past perturbations have done so. We use functional diversity to describe how the structure of North American mammal communities changes over the past 66 Ma, an interval spanning the rebound radiation following the K/Pg and several subsequent environmental disruptions including the PETM, the expansion of grassland, and the onset of Pleistocene glaciation. For 264 fossil communities, we examine three aspects of ecological function: functional evenness, functional richness, and functional divergence. Shifts in functional diversity are significantly related to major ecological and environmental transitions. All three measures of functional diversity increase immediately following the extinction of the non-avian dinosaurs, suggesting that high degrees of ecological disturbance can lead to synchronous responses both locally and continentally. Otherwise, the components of functional diversity respond differently to environmental changes and are decoupled for the last ~56 million years.