Some of Lucy’s primitive features, such as the orientation of her shoulder, suggest that she might have spent some time in the trees (arboreal). The scapula (shoulder blade) articulates with the humerus (upper arm bone) at the scapula’s glenoid fossa, a small circular or oval depression located on the scapular head. A cranially (up, toward the head) oriented glenoid fossa enhances an animal’s ability to climb or use forelimb-dominated activities where the arms are held above the head. Like chimpanzees, and unlike humans, the A. afarensis glenoid fossa faced cranially, suggesting Lucy probably used above-head arm postures, consistent with the idea that she may have climbed trees11,13