EFFECTS OF CLIMATE ON MAMMALIAN SPECIES DIVERSITY AND COMMUNITY STRUCTURE DURING THE TERTIARY IN THE NORTHERN GREAT PLAINS, UNITED STATES

We examined the effects of climate change on mammalian species diversity and community structure from 30 to 9 million years ago in the northern Great Plains. Species records were acquired from the MIOMAP database, a relational database of western North American fossil mammals that is currently under construction at the University of California, Berkeley. All records were from a limited geographic range (southeastern Wyoming, southern South Dakota, and northern Nebraska) and separated into 11 time intervals based on currently accepted subdivisions of the North American land mammal ages. The effect of climate change on species richness was evaluated by comparing the global oxygen isotope curve to a species diversity curve corrected for sampling bias. Changes in community structure were assessed by qualitatively comparing mammalian body mass distributions (cenograms) from successive time intervals to each other as well as to the oxygen isotope curve. Our results suggest that: (1) contrary to prior reports, changes in species diversity in the northern Great Plains do appear to relate to shifts in the oxygen isotope curve, (2) no clear relationship was found between climate change and community structure, and (3) a shift from a more open, arid habitat to a more forested, humid environment appears to have occurred during the Mid-Miocene Climatic Optimum.