Question

What adaptations for bipedal locomotion are found in the legs?

Answer 1

The foot skeletal structure.

Explanation:

The key distinguishing feature of bipedal creatures from others is the unique arrangement of bones and muscles in the foot that allow for the essential balance functions.

Simpler foot structures, and even masses like hoofs are sufficient for locomotion with four limbs. The peculiar requirements of dynamic balance on only two appendages are met with the ankle/foot connection, extended forward foot with slight backward heel, and significantly the flexible toes which provide fine motor control for stability.

Other characteristics such as leg bone orientation and musculature are not essential to the differentiation of quadrupedal from bipedal motion, although they may make it more efficient.

In humans the feet must support and propel the entire body on their own instead of sharing the load with the forelimbs. In humans the heel is very robust, and the great toe is permanently aligned with the four diminutive lateral toes.

Unlike other primate feet, which have a mobile midfoot, the human foot possesses (if not requires) a stable arch to give it strength. Accordingly, human footprints are unique and are readily distinguished from those of other animals.

Good discussion and graphics here:
https://www.britannica.com/science/human-evolution

http://www.sciencedirect.com/science/article/pii/S0021929002004190