Xal Dimorphism in the Mallard Duck

Long arms demonstrated that tree dwelling was very commonplace, and most likely necessary to avoid predation from africa's diverse and dangerous wild life. They still had large jaws and teeth compared to modern humans, and the brain case was small, much more like a modern chimpanzee. So if we are to assume that the astralapithesenes are ancestral to modern humans then the bipedal adaption was something that occurred before we became extremely intelligent and before we became expert tool makers.