1. Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560–0112, USA.
2. Division of Paleontology, National Museums of Kenya, P.O. Box 40658, Nairobi, Kenya.
3. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA.
4. Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA.
5. Research Laboratory for Archaeology, University of Oxford, 6 Keble Road, Oxford, OX1 3QJ, UK.