M. R. Bennett, J. W. Harris, B. G. Richmond, D. R. Braun, E. Mbua, P. Kiura, D. Olago, M. Kibunjia, C. Omuombo, A. K. Behrensmeyer, D. Huddart, and S. Gonzalez. Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya. Science, volume 323, issue 5918, pages 1197-1201, 2009.