ACKNOWLEDGMENTS
I thank C. Argot, C. Bens, R. Bobe, Y. Desta, C. Guillemot, M. Leakey, M. J. Lesur-Gebremariam, E. Mbua, M. Muungu, and G. Senishaw for their help and permission to work in the various collections, P. Martini and A. C. Nanda for sharing data, and E. Scott and J. Harris for their comments on the manuscript.