Paleontology and Primate Evolution in the Late Oligocene of Kenya

Washington University, Saint Louis MO

Investigators

Abstract

One of the great gaps in the fossil record of the primate group containing Old World monkeys, apes and humans (catarrhines) has been the one spanning the interval from about 30 to 20 million years ago in Africa. This gap has now been filled by two sites of Late Oligocene age (approximately 24-27 million years old) in northwestern Kenya, both of which yielded new primate fossils during preliminary fieldwork in June, 2007. The current research is designed to find more primate fossils representing more complete skeletal remains from the new research areas, to put the primates into a solid framework of geological age and paleoenvironment, and to conduct phylogenetic and paleobiological analyses of them. Field camps will be established at the sites of Nakwai and Losodok, and research will be conducted with an interdisciplinary crew of anthropologists, paleontologists, geologists, including students, to recover primate fossils, other mammals, reptiles and birds, fossils of paleoenvironentally important plants, and rock samples for radiometric, paleomagnetic, and geo-isotopic studies. Together, analyses of these data will document patterns of primate evolution and paleoenvironment during the Late Oligocene of Kenya. This work will be integrated into existing knowledge of the important basal catarrhines of the early Oligocene and the great radiation of apes in the early Miocene, in order to better understand the evolutionary transition from primitive, early catarrhines to the earliest large-bodied apes of the superfamily Hominoidea. Several issues of theoretical importance will be addressed. Some issues center around taxonomic assessments of Late Oligocene catarrhines: were true hominoids (members of the group containing only apes and humans) present at this time, or are the fossil ape-like primates precursors, or lateral relatives, of true hominoids? Had the evolutionary split between Old World monkeys and apes occurred by this time, as predicted by the latest molecular clocks? Other issues of theoretical importance center around the adaptations of these early ape-like primates, and the sequence in which they acquired ape-like traits, such as skeletal adaptations for their characteristic climbing movements, dental adaptations for frugivorous diets, and cranial adaptations associated with increasing brain size. The Late Oligocene is the period in which Africa, previously an island continent, was beginning to dock with the northern continents, and there is considerable theoretical interest in whether this geographic event was associated with African climatic change, shifts in environment or ecology, or changes in animal communities. Kenyan students and museum staff will be participate in this project, and many of the key analyses and laboratory procedures will be conducted with Kenyan colleagues, providing new opportunities and training for Kenyan paleontologists.