Improved age control on early Homo fossils from the upper Burgi Member at Koobi Fora, Kenya Monika V. Knul, Trine Kellberg Nielsen, Jeroen H.J.L. van der Lubbe, Mark J. Sier, Guillaume Dupont-Nivet, H.B. Vonhof, Josephine C.A. Joordens, Fred Spoor, G. R. Davies, C.S. Feibel • 2013