Mammalian Faunas Across the Middle-Late Paleocene Boundary in Western North America

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The Paleocene Epoch represents the time during which mammals, particularly placentals, underwent a major adaptive radiation and became dominant land animals. Almost one-half of the known ordinal diversity of Genozoic mammals is thought to have arisen in the Paleocene, and many of these first appearances are in North America. This geologic interval is therefore of great importance in the history of mammals, yet less is known about mammalian diversity and composition during the Paleocene than during any of the later epochs of the Genozoic. Particularly weak is our knowledge of mammalian history during the transition from the middle to late Paleocene (i.e., from the Torrejonian ıTo! to the Tiffanian ıTi! North American Land-Mammal Ages), when there was a significant change in the fauna. This faunal turnover was previously ascribed to climatic change and intercontinental migrations; however, our recent work indicates that no major immigrations into the Western Interior occurred near the boundary, and that the scenario of faunal change was more complex than previously hypothesized. By substantially increasing the number of large samples near the To/Ti boundary, this project will have provided the most detailed information with which to study faunal turnover during this important interval. Preliminary collections from one locality n particularly. Bingo Quarry,indicate that it is crucial to our understanding of the To/Ti transition. Study of these samples, including those from Bingo Quarry, will significantly augment knowledge of the phylogeny, functional morphology, paleoecology, and biostratigraphy of To/Ti mammals and provide the foundation for analyses of faunal turnover.