The provided diagram delineates the skeletal systems of the Australopithecus afarensis and the Homo erectus. Overall, the former is characterized by the capabilities of walking and climbing trees, while the latter is known to be highly efficient in walking and running with considerable endurance.
The comparison between the Australopithecus afarensis and the Homo erectus reveals unique features. Notably, the head and snouts of the two differ drastically, being unbalanced and long versus balanced and short. Moreover, the Australopithecus afarensis has a wider chest and a longer forearm, but possesses high, narrow shoulders and short, wide waist. Meanwhile, the Homo erectus develops low, wide shoulders and tall, narrow waist at the expense of the narrow chest and short forearm.
In regard to the lower bodies, the Australopithecus afarensis, which has a long femoral neck and small gluteus maximus, stands in contrast with the Homo erectus. However, below the femoral neck, the Homo erectus surpasses the other in the development of hip, knee, ankle joints and heel bone, which are larger. A longer Achilles tendon and a stabilized foot arch with short toes are also observed in this ancestor, although in the case of the Australopithecus afarensis, the tendon is shorter and foot arch is partial with long toes.
In conclusion, skeletons of the two hominid species show distinct adaptation in specific regions in accordance with their daily activities.