Paleoenvironments, Paleoecology, Adaptations, and the Origins of Bipedalism in Hominidae

Abstract

The discovery of 6 Ma bipedal Orrorin in a heavy woodland to forest paleoenvironmental setting indicates that bipedalism most likely evolved in relatively closed vegetation formations of the kind that are common in Soudanian, Somali-Masai, and Zambezian centers of endemism and in the transition zones between these centers and the Guineo-Congolian center of endemism. It is much less likely that it evolved in savanna settings, such as are typical of Sahelian and Kalahari centers of endemism or even more open vegetation formations. In short, it was not only environmental change that drove the origin of bipedalism as has been thought by many researchers for the past century or more, but also a change in ecology. Of course, open environments had to be present for them to be occupied, but their formation did not immediately result in their occupation by hominoids. Indeed it took tens of millions of years before an ape lineage evolved the prerequisite adaptations for such a development to take place. These adapatations were initially locomotor in nature, but later incorporated dietary (dental and digestive tract modifications), the storage of reserves of fat within the body, and behavioral changes, all of which resulted in greater eurytopy. It is considered most likely that bipedalism evolved in forested to well-wooded environments, and only later did bipedal hominids venture into more open country. Thus bipedalism was a development which subsequently enabled hominids to invade open country. It was not invasion of open country that led to bipedalism as so often thought.