THE MIDDLE-EOCENE MAMMALIAN FAUNAL SUCCESSION IN SAN DIEGO AREA, SOUTHERN CALIFORNIA

The middle-Eocene vertebrate fossil assemblages from San Diego County, California, provide a rich record of regional faunal succession over a period of 6 to 9 million years that witnessed drastic changes in the climate and vegetation. To date, however, the reconstruction of faunal succession has been temporally coarse, owing to the dearth of radiometric and magnetostratigraphic age estimates that can be tied to the fossil localities. As a step toward increasing the temporal resolution of fossil occurrence data, I applied the disjunct distribution ordination to mammalian assemblages from 53 localities of the Uintan and Duchesnean North American Land Mammal Ages (~46-37 Ma). The preliminary result suggests a modest increase in generic richness from the early Uintan to the late Uintan, followed by a substantial decrease during the Duchesnean. The latter phase is marked by the disappearances of an ecologically-diverse array of taxa, but those of primates, artiodactyls with low-cusped teeth, and carnivoramorphans that are well adapted for climbing are consistent with the vegetational and habitat structural changes that have been inferred from the regional pollen record.