Question

Speaking of Don Johanson and his find of Lucy. Assume that you are in the laboratory analyzing the Lucy Australopithecus afarensis skeleton. You have also the complete skeletons of the chimpanzee and the modern human. a) Which are more similar to the human and show definitively that she is BIPEDAL? b) Which parts of the Lucy skeleton are more similar to the chimpanzee?

Answer 1

In 1974, paleoanthropologist Donald C Johanson discovered a 3.2 million year old fossil of a female skeleton in Ethiopia that changed the understanding of human origin. It was found to be the skeleton of Australopithecus afarensis, known to the world as Lucy.

There is considerable debate surrounding the locomotor behavior of A. afarensis. Some studies have suggested that A. afarensis is exclusively bipedal (using only two legs for walking), while others suggest that the creatures were partly arboreal (which means they had structures aiding to climb trees).

a) Similarities with humans that shows bipedalism

• The pelvis is very much human like (but not wholly, pelvic of A. afarensis is wider, with laterally oriented iliac blades)
• The iliac blades are short and wide.
• Sacrum is wide and positioned directly behind the hip joint.
• Attachment of knee extensors.
• Femur angles in towards the knee from hip which allowed the foot to have fallen closer to the midline of the body indicating habitual bipedal locomotion.
• The feet has adducted big toes suggesting the difficulty (but not impossible) to grasp branches with the hind limbs.
• Loss of abductable great toe which suggests the loss of ability to grasp branches with foot.
• Bones of the foot like calcaneus also indicate bipedality.

All these features suggest that A. afarensis was able to walk like modern humans and was quite an efficient bipedal walker over short distances.

b) Similarities with chimpanzee

• Anatomy of hand, feet, and shoulder joints.
• Curvature of the finger and toe bones (phalanges) suggest the ability of to grasp branches and climb trees.
• Presence of wrist-locking mechanism suggests knuckle walking.
• Cranial orientation of shoulder joint.
• Presence of long arms is reflective of heightened ability to use the arm above the head while climbing trees.
• Presence of large jaws and powerful jaw muscles.