||Position of the foramen magnum
||Positioned inferiorly (immediately under the cranium) so that the head rests on top of the vertebral column for balance and support (head is perpendicular to the ground).
||Posteriorly positioned (to the back of the cranium). Head is positioned parallel to the ground.
||Shorter upper limb (not used for locomotion).
||Longer upper limbs (used for locomotion).
||S-curve due to pressure exerted on the spine from bipedalism (lumbar lordosis).
||Robust lumbar (lower-back) vertebrae (for shock absorbance and weight bearing). Lower back is more flexible than that of apes as the hips and trunk swivel when walking (weight transmission).
||Gracile lumbar vertebrae compared to those of modern humans.
||Shorter, broader, bowl-shaped pelvis (for support); very robust. Broad sacrum with large sacroiliac joint surfaces.
||Longer, flatter, elongated ilia; more narrow and gracile; narrower sacrum; relatively smaller sacroiliac joint surface.
||In general, longer, more robust lower limbs and more stable, larger joints.
- Large femoral head and longer neck (absorbs more stress and increases the mechanical advantage).
- Valgus knee, in which the angle of the knee positions it over the ankle and keeps the center of gravity balanced over the stance leg during stride cycle (shock absorbance).
- Distal tibia (lower leg) of humans has a large medial malleolus for stability.
|In general, smaller, more gracile limbs with more flexible joints.
- Femoral neck is smaller in comparison to modern humans and shorter.
- The legs bow outward, and there is no valgus angle of the knee (no “knock knees”).
- The distal tibia in chimpanzees is trapezoid (wider anteriorly) for climbing and allows more flexibility.
||Rigid, robust foot, without a midtarsal break.
||Flexible foot, midtarsal break present (which allows primates to lift their heels independently from their feet), opposable big toe for grasping.