Human-like external function of the foot, and fully upright gait, confirmed in the 3.66 million year old Laetoli hominin footprints by topographic statistics, experimental footprint-formation and computer simulation.
Crompton RH, Pataky TC, Savage R, D'Août K, Bennett MR, Day MH, Bates K, Morse S, Sellers WI. J R Soc Interface. 2012 Apr 7; 9(69):707-19. Epub 2011 Jul 20.