The study of fossil comunities has much to offer ecologists, as well as paleontologists. The fossil record can provide communities undisturbed by human influence over a time scale that chronicles the influence of historical processes, such as extinction and immigration, on community structure. Trophic diversity within the guild of large, terrestrial mammalian predators in North America over the last 37 million years will be explored. The paleoguilds, separated in age by two to four million years, will be compared over time to a sample of four previously analyzed Recent guilds. The sampled paleofaunas include some which precede or follow mass extinction events, and some that are missing such typical modern carnivores as cats and hyaenas. Using an ecomorphological approach, trophic diversity will be assessed by body size and previously demonstrated, functional measurements of canivore teeth. Measurements include estimates of slicing, grinding and bone-crushing abilities and reflect the relative proportion of meat, bone, and non-vertebrate foods in the diet. A principal component analysis will be applied to these data to create a multivariate morphospace in which to view the distribution of species within guilds. Species packing, as measured by Euclidean distance between taxa, will be compared among guilds with hypothetical, randomly generated guilds. In addition, the number and body size distribution of prey species will be quantified for each time period to explore the influence of resource characteristics on guild composition. Results should suggest general rules, if they exist, of predator guild structure that are likely to have broad implications for community ecology.
