When held in the anatomical position, the femur of an ape will stand almost vertical within a horizontal plane. In humans, the femur will form a bicondylar angle (i.e. the angle at which the femur lies to the midline of the body), and brings the knees closer together (valgus knee). Because of this angle, the feet fall directly below the center of gravity, balancing the body over the stance leg during the stride cycle, thereby stabilizing bipedal locomotion. Lucy’s femur exhibits a bicondylar angle.

The size of the femoral head is related to body mass. The large femoral head of modern humans reflects their larger body size. Comparing Lucy with modern humans, Lucy has a smaller femoral head and a relatively longer femoral neck. Reduction of the femoral neck length increased the amount of stress the femur was able to support, and may have been a specialization due to a change in bipedal posture or an adaptation for the larger body size of later humans.

The condyles of the distal femur are smaller and more round in primates, but are more elliptical and larger in humans. Lucy's condyles are large as seen in bipeds. The relative size of the condyle is an adaptation which supports the leg during locomotion. The larger condyles help to support the leg due to the increased weight transfers of bipedal locomotion.

The chimpanzee pelvis is taller relative to its width and the iliac ala are more flat than seen in modern humans, lying roughly parallel with the plane of the back. In modern humans, the iliac alae are curved forward and flare more to the sides of the body. Lucy has the broader hips and the flaring iliac alae, all hallmarks of bipedal locomotion. However, the pelvis is wider in modern humans that in Lucy. The more widely spaced hip joints and the broader pelvic outlet is a critical adaptation that allows enough space for the larger brained babies of modern humans to pass through the birth canal. During the widening of the pelvic outlet, the hip joints (acetabulum) are moved further away from the body’s center of gravity. This exerts more force on the femoral head during locomotion. An increase in the size of the femoral head helps to counteract these forces.

The size of the sacroiliac joint surface is related to the amount of weight transmitted through the pelvis during locomotion. As humans walk, the pelvis must cope with the stress of weight transfer, while quadrupedal chimpanzees are able to alleviate some of this stress through the support of their upper limbs. Thus, the surface size of the sacroiliac joint in humans is much larger than that seen in chimpanzees. Lucy has a large sacroiliac joint surface as is expected of bipeds.

Additionally, the angle of curvature of the sacrum reflects that of the lumbar curvature, and is more pronounced in humans while the chimpanzee sacrum is straight. Lucy's sacrum shows some curvature, but is not as pronounced as in modern humans.

In humans, the lumbar vertebrae are much larger than those seen in the great apes. In addition, modern humans have five lumbar vertebrae while the apes typically have only four. An increase in the number of vertebrae enhances flexibility of the trunk, reducing the distance the hips must swivel forward during bipedal locomotion, and producing a more efficient stride. In addition, the human spinal column demonstrates a very distinct curve, known as the lumbar curvature. This helps to bring the body’s center of gravity closer to the midline and above the feet. Also, the relatively larger size of the human lumbar vertebrae to that of apes indicates an adaptation to the greater amount of stress transferred through the trunk and into the hips.

Lucy's vertebrae are broad and articulate to form a distinct lumbar curve, as is seen in modern humans. The fragmentary remains also indicate that Australopithecus most likely had five or six lumbar vertebrae.

In primates, the degree of phalangeal shaft curvature is directly related to the frequency of arboreal behavior. Curved fingers and toes aid in the ability to grasp onto a curved branch. Species that spend a great deal of time in suspensory behaviors have more curved phalangeal shafts, while species not habitually suspensory have relatively flat phalangeal shafts. When comparing human phalanges with those of chimpanzees, the shaft of the human phalanx is relatively straighter than a chimpanzee. Lucy shows an intermediate curvature between those of modern humans and chimpanzees, which suggest that Lucy was still engaged in some amount of arboreal behaviors.

Primates that move by quadrupedal locomotion have longer arms (forelimbs) relative to their legs (hindlimbs), while bipedal humans have longer legs than arms. In comparison, Lucy maintains relatively longer arms to her legs.

Lucy's humerofemoral ratio is 84.6. The mean of this measurement in humans is 71.8, indicating humans have shorter arms relative to their legs. The common Chimpanzee measurement is 97.8. In other words, Lucy appears to have intermediate measurements between modern humans and chimpanzees.

The most notable difference between the teeth of a modern human and a modern chimpanzee is the smaller canines seen in humans. The canines of A. afarensis are relatively smaller than those seen in modern chimpanzees, but are still relatively large compared to modern humans.

A. afarensis incisors are more similar to the size and shape of modern chimpanzees, and the molars are relatively larger than in modern humans. Also, tooth enamel is thicker in A. afarensis than in modern humans.

The text for this element is coming soon.

The text for this element is coming soon.

The text for this element is coming soon.

The text for this element is coming soon.

The text for this element is coming soon.

The text for this element is coming soon.

The chimpanzee pelvis is taller relative to its width and the iliac ala are more flat than seen in modern humans, lying roughly parallel with the plane of the back. In modern humans, the iliac alae are curved forward and flare more to the sides of the body. Lucy has the broader hips and the flaring iliac alae, which are all hallmarks of bipedal locomotion. However, the pelvis is wider in modern humans than in Lucy. The more widely spaced hip joints and the broader pelvic outlet is a critical adaptation that allows enough space for the larger brained babies of modern humans to pass through the birth canal. During the widening of the pelvic outlet, the hip joints (acetabulum) are moved further away from the body’s center of gravity. This exerts more force on the femoral head during locomotion. An increase in the size of the femoral head helps to counteract these forces.

The text for this element is coming soon.