N. Ashton, S. G. Lewis, I. D. Groote, S. M. Duffy, M. Bates, R. Bates, P. Hoare, M. Lewis, S. A. Parfitt, S. Peglar, C. Williams, and C. Stringer. Hominin footprints from early Pleistocene deposits at Happisburgh, UK. PLoS One, volume 9, issue 2, pages e88329, February 2014.