The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Small mammal assemblages from the Chadron Formation of Nebraska and implications for understanding late Eocene primate community ecology


1Anthropology Program, Saint Cloud State University, 2Department of Anthropology, University of Montana, 3Department of Anatomy, Des Moines University

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The end of the Eocene in North America is characterized by climatic change, faunal turnover, and an associated decline in primate diversity. While primates survive in tropical refugia during the late Eocene, they eventually go extinct in the Oligocene of North America. Gaps in the distribution of fossiliferous late Eocene deposits and knowledge of small mammal communities limit our understanding of this critical period in North American primate evolution. As a result, we have undertaken paleoanthropological fieldwork in late Eocene Duchesnean- and Chadronian-aged deposits within the Oglala National Grassland of northwestern Nebraska in order to address small mammal diversity during this important period.

In this paper, we present preliminary analyses of small mammal fossils from a concentration of anthill accumulations in the late Eocene, Peanut Peak Member of the Chadron Formation in northwestern Nebraska. The relative concentrations of small mammal taxa were calculated on the basis of mandibular and maxillary premolar and molar taxonomic identifications. To date, our faunal concentrations are: Multituberculata (0.5%), Marsupialia (4.0%), Insectivora (11.1%), Primates (0.25%), Lagomorpha (6.8%), Rodentia (66.5%), and Carnivora (10.8%). These percentages are similar to previously reported data from the nearby Chadronian-aged Raben Ranch locality, despite disparate taphonomic agents accumulating the fossils. These data expand our knowledge of an important period in North American primate evolution, during which there is a change in the taxonomic composition of small mammal communities accompanied by a decline in primate diversity.

This study was funded by an IOER Research Grant, project number 2010-20.

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