Final answer:
Primates have skeletal features such as rotating shoulder joints, a separated big toe, and stereoscopic vision that are adaptations to an arboreal lifestyle. These evolutionary traits support their tree-dwelling origin.
Step-by-step explanation:
Many skeletal features of the primates reflect a tree-dwelling or arboreal adaptation. These include rotating shoulder joints, a big toe that is widely separated from the other toes (providing a better grip, except in humans), and stereoscopic vision, which enables depth perception crucial for judging distances between tree branches. Additionally, primate traits like larger brain size, the transformation of claws into flattened nails, and the tendency to carry the body upright all support the arboreal theory that primates evolved for a life among the trees.