Fossil deposits on the Kenyan islands of Rusinga and Mfwangano comprise one of the richest sources of information for understanding the origin and diversification of the earliest apes. Best known for the primitive ape Proconsul and catarrhine primates Dendropithecus, Nyanzapithecus, and Limnopithecus, Rusinga/Mfwangano sites also preserve copious mammal, reptile, bird, and invertebrate fossils, as well as rarely seen fossil elements such as leaves, seeds, fruits, and insects. Thus, it becomes possible to reconstruct not just the anatomy of these primates, but also their chronological context, aspects of their feeding ecology, habitat preferences, and the broader ecological community in which they thrived. This project will undertake new research on Rusinga/Mfangano to further our knowledge of the chronology and paleoecology of stem catarrhines and hominoids. Specific objectives are to: 1) establish stratigraphic and chronological control within and among primate fossil sites on Rusinga and Mfangano; and 2) reconstruct paleoenvironmental conditions throughout the geological sequence to assess the ecological parameters in which these primates lived. Work will be carried out over three summers and include basic stratigraphic analysis, absolute and relative dating, controlled fossil collection, analyses of stable isotopes, revisions of existing faunal collections, and dental microwear analysis. The intellectual merit of this project lies in combining geological, paleontological, and paleoecological methodologies to substantially advance our knowledge of hominoid evolution and adaptation through development of high-resolution chronostratigraphic data and detailed paleoecological models for Rusinga and Mfangano catarrhine primates. This project also has considerable broader impact in promoting education and cooperation at the local level, advancing local involvement in the preservation of the fossil heritage, employing local and national Kenyan workers, educating undergraduate and graduate students, and promoting international and interdisciplinary collaborations.