The diagram compares skeletal systems of two different ancestors of modern human beings: Australopithecus afarensis and Homo erectus.
Firstly, as a walker and tree climber, had relatively large body proportions. This skeleton had an unbalanced head with a long snout, as well as large eyes and ears. In addition, Australopithecus afarensis had high and short shoulders, which gave it a distinctive appearance. It had a wide chest and a short wide waist. Other features: long forearm, small gluteus maximus (not shown), and a long femoral neck. The skeleton of Australopithecus afarensis also had small hips, knee and ankle joints with a short Achilles tendon, a small heelbone, long toes, and a partial foot arch.
Secondly, Homo erectus (walker and endurance runner) had distinct body measurements. It had noticeable features compared to the first species it had balanced head (short snout), low and wide shoulders, narrow chest, tall and narrow waist, short forearm with big gluteus maximus (not shown).
Furthermore, in comparison to australopitecus afarensis, homo erectus had short femoral neck, large hip with knee and ankle joints. It had long achilles tendon, enlarged heelbone and short toes with a stabilized foot arch.
To sum up, it can be said that Homo erectus had a more stable posture and more balanced body proportions than Australopithecus afarensis. Additionally, the appearance and skeleton of Homo erectus are closer to those of modern human beings.