Fossils will be collected from middle Miocene deposits in the Mojave Desert of southern California. This work is undertaken to develop a secure biostratigraphic framework for Hemingfordian mammal assemblages, which when combined with the existing Barstovian mammal assemblages will permit reliable identification of the boundary between Hemingfordian and Barstovian land mammal ages. Preliminary study has indicated the Mojave Desert is the best area to develop a dependable Hemingfordian/Barstovian boundary. The Cenozoic history of mammals is punctuated with brief but significant intervals of intercontinental dispersal by land mammals. Middle Miocene is one of these intervals, with the Hemingfordian/Barstovian boundary possibly the high point in appearance of immigrants. Secure chronologic resolution of that boundary is necessary to test hypotheses about the timing of global climatic-eustatic sea level events as a trigger mechanism for intercontinental dispersal of land mammals. This project will provide primary data for testing these hypotheses and should clarify the interaction of dynamic global processes in the evolution of terrestrial biota.
