NORTH AMERICAN MAMMAL PREDATOR DIVERSITY AND FUNCTIONAL TRAIT RESPONSE TO CLIMATE CHANGE ACROSS THE CENOZOIC

The general trend of global cooling across the Cenozoic transformed the North American landscape, resulting in various dietary and locomotory adaptations in herbivores in response to the expansion of open grasslands. In contrast, the material properties of muscle, skin and bone have not changed over the transition, suggesting a potential lack of both taxonomic and functional response in North American predators due to their unchanging resource. To test this hypothesis, we assembled a dataset containing body mass estimates and relative blade length (RBL) of the first lower molar, an index of carnivory, for nearly all (n = 394) Cenozoic North American mammal predators (Creodonta and Carnivora). The mean RBL increases sharply in the late Eocene, with the Oligocene and onward predator faunas having higher mean RBL, suggesting a potential functional response to the decline of forested environments following the Eocene-Oligocene Transition. To establish the degree to which predator functional traits correlate with environment, we tested our extant dataset for associations between the measured functional traits and diet and habitat type, respectively. To test if changes in functional traits are due to taxonomic turnover, we ran a model comparison approach to find the best-fit configuration of distinct shifts in both taxonomic composition and functional trait distributions. While we found no association with body mass, we found a significant association between RBL and both habitat type and diet, with higher RBL taxa preferentially found more open environments. Our best fit models found a general decoupling of the placement of the shifts for taxonomic composition and functional trait distribution. These results indicate a potential functional response, rather than simply phylogenetic replacement, in North American predators to large-scale environmental changes across the Cenozoic.