Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Primates constituted a dominant part of the mammalian faunas of North America during the early and middle parts of the Eocene: 55-46 ma). Beginning in the Uintan North American Land Mammal Age: 46-42 ma) primates declined in diversity and abundance in the Rocky Mountain region. This decline has been linked to the recession of tropical rain forests out of northern latitudes at that time. Climatic change of this magnitude would presumably have an impact on the contemporary mammalian faunas, with reduction or extinction of forest groups like primates, but perhaps radiation of mammals that preferred more open habitats such as artiodactyls. In this dissertation I describe and analyze the postcranial morphology of Uintan mammals from the Uinta Formation in Utah to address which lineages evolved to take advantage of arid habitats and which did not. The primary goal of this dissertation is to examine the relationship between mammalian postcranial functional adaptations and habitat change in the Uintan and its implications for primate decline. To this end I:: 1) describe and analyze new fossil skeletal material from primates, rodents, insectivores and primitive eutherian mammals to reconstruct the paleobiology of these groups,: 2) identify measurements of the astragalus and distal humerus that consistently discriminate open-country from closed-country taxa in a diverse sample of modern mammals, and: 3) apply the astragalar measurements to a sample of artiodactyl astragali from the Uinta Formation to evaluate morphological responses to habitat change stratigraphically. My results suggest that groups of mammals that show features related to increasing terrestriality or cursoriality in the late Uintan compared to their early Uintan or Bridgerian ancestors continue to radiate after the Uintan, whereas those that retain forest or aquatic adaptations become increasingly scarce after the Uintan. Further, I suggest that artiodactyls acquire astragalar features related to locomotion in an open-habitat gradually throughout the Uintan possibly tracking gradual habitat changes, rather than abruptly as would be expected if they were responding to a sudden drying event. These results strengthen evidence for a link between primate extinction and loss of forests in the middle Eocene.
Dunn, Rachel, "Mammalian Postcranial Evolution and Primate Extinction in the Middle Eocene of North America" (2009). All Theses and Dissertations (ETDs). 95.