The diagram illustrates the skeletal systems of two ancestors, Australopithecus afarensis and Homo erectus. Overall,the main differences between them are related to body proportions, as Australopithecus afarensis had relatively larger and wider body parts, while Homo erectus possessed smaller features that were better suited for walking and running long distances.
In the upper half of the body,Australopithecus afarensis had an unbalanced head with a long snout, high narrow shoulders, and a wide chest. In contrast, Homo erectus had a balanced head , low wide shoulders, and narrow chest. Furthermore, Australopithecus had a long forearms and small gluteus muscles, whereas Homo erectus had shorter forearms and bigger gluteus muscles.
Turning to the lower half of the body,Australopithecus afarensis had a long femoral neck , long toes, and partial food arch. By contrast, Homo erectus had shorter femoral neck,shorter toes and stabilized foot arch. In comparison,Australopithecus had a small hip and ankle joints,and short Achilles tendon,while Homo erectus had large hip and ankle joints,and longer Achilles tendon.