Final answer:
The Lucy (Au. afarensis) skeleton differs from the human (Homo sapiens) skeleton in the length and curvature of finger and toe bones, as well as the shape of the pelvis.
Step-by-step explanation:
Two postcranial traits that differ between Lucy (Au. afarensis) and human (Homo sapiens) skeletons are the length and curvature of the finger and toe bones, as well as the shape of the pelvis.
Au. afarensis, like other great apes, had long and curved finger and toe bones, which are adaptations for climbing and hanging from branches. In contrast, the finger and toe bones of humans are shorter and less curved, reflecting our adaptation to bipedal locomotion.
The shape of the pelvis is also different between Au. afarensis and humans. Au. afarensis has a shorter and wider pelvis, similar to that of modern humans, indicating a transition to bipedalism. This change in pelvic shape allows for efficient walking on two legs.