Approximately 4,100,000+ BC: Hominids are definitely walking upright now, if not earlier
Australopithecus anamensis looks very much like a near hairless chimpanzee. Males tend to be much larger than females.
-- ONLINE NEWS May 27, 1998 Early Bipedalism Confirmed ["http://www.he.net/~archaeol/online/news/biped.html"] by ANGELA M.H. SCHUSTER, the Archaeological Institute of America