Bipedalism: Major difference between humans and other primates is that humans are bipedal. Mary Leakey discoverd the loetoli footprints. There were three sets of footprints of early hominins these footprints were bipedal. Having a strong heel strike, distinct arch, and big toe inline with heel. These footprints indicate that bipedalism occured almost 3.6 million years ago. The traits that mark bipedalism are an s shaped spine, a wide flat pelvis, a slanting thigh bone, a double arched foot, and a big toe inlined with the heel.