With the extinction of non-avian dinosaurs, the Paleocene epoch (roughly 65 to 55 million years ago) was a critically formative interval in the evolutionary history of modern mammals. Turnover in the composition of the mammalian fauna during the Paleocene, and particularly between the Torrejonian (To) and Tiffanian (Ti) North American Land Mammal Ages, was among the most significant during the Cenozoic, the so-called Age of Mammals. It is then that mammals underwent rapid diversification and became dominant land animals. The causes and mechanisms of Paleocene mammalian faunal turnover have been variously ascribed to either climatic change or pseudo-extinction but the data required to test these hypotheses have, heretofore, been wanting. This proposal seeks to document the pattern of To/Ti mammalian faunal turnover by employing massive samples of largely undescribed fossils, collected by Stony Brook University field crews in the 1980s and early 1990s from the eastern Crazy Mountains Basin (CMB), Montana. When studied in the context of the careful litho-, magneto- and biostratigraphic analyses proposed here, the samples from these localities will provide data crucial for a revision of the biochronology of the Paleocene epoch. The proposed project will also result in exploitation and realization of the vast potential of a poorly known and under-sampled site, the Bangtail locality, on the western side of the basin. Limestones from Bangtail have begun to yield some of the most complete and exquisitely preserved mammalian skulls and skeletons yet known for the Paleocene. The samples from both the eastern and western sides of the CMB will significantly augment knowledge of the phylogeny, functional morphology, and paleoecology of Paleocene mammals. Identification, description, and analysis of these samples, coupled with new paleoclimatic data based on paleofloras and stable isotope analyses of mammalian teeth, will be employed to address long unanswered and increasingly controversial questions concerning the mechanisms and causes of rapid faunal turnover during the Paleocene.
