I was reading Ancestor's Tale the other day and it mentions that earliest hominid fossils [before most of the change in hominid brain size] push very close to the common ancestor of humans and chimpanzee/bonobos. These are considered to be bipedal from the likely position of the neck. So what do you think would be the best explanation? Do you think the molecular clock is wrong? Evolution of bipedalism was swift? The common ancestor was more human-like? The palaeontologists were wrong?