Y. Sawada, M. Saneyoshi, K. Nakayama, T. Sakai, T. Itaya, M. Hyodo, Y. Mukokya, M. Pickford, B. Senut, S. Tanaka, T. Chujo, and H. Ishida. The Ages and Geological Backgrounds of Miocene Hominoids Nacholapithecus, Samburupithecus, and Orrorin from Kenya. Human Origins and Environmental Backgrounds, Springer US, pages 71-96, 2006.

Y. Sawada, M. Pickford, B. Senut, T. Itaya, M. Hyodo, T. Miura, C. Kashine, T. Chujo, and H. Fujii. The age of Orrorin tugenensis, an early hominid from the Tugen Hills, Kenya. C. R. Palevol, Elsevier BV, volume 1, issue 5, pages 293-303, December 2002.

Y. Sawada, T. Miura, M. Pickford, B. Senut, T. Itaya, C. Kashine, M. Hyodo, T. Chujo, and H. Fujii. {O-27} The age of Orrorin tugenensis, a late Miocene hominid, from the Tugen Hills, Kenya. 日本地質学会学術大会講演要旨, jstage.jst.go.jp, volume 2001, pages 15, 2001.