Question

What adaptations for bipedal locomotion are found in the legs?

Answer 1

Bipedal locomotion refers to animals that stand and move using only two legs. It is the movement of an animal on two legs while being in an upright position. Running, hopping, walking are some examples of bipedal movements. All humans and some animals exhibit obligate bipedalism. However, the earliest ancestors of humans were quadrupeds and they evolved eventually to walk upright in a bipedal fashion via natural selection.

Complete answer:
Obligate bipedal species have highly specialized skeletal adaptations to facilitate this kind of locomotion. The adaptations occur mostly within the soft tissue of the body like muscles and tendons.
Majority of the adaptations are found in the post cranial region i.e the skeleton from below the head. These adaptations provide strength and stability to the lower limb, thus allowing for more shock absorption. They also support the skeleton by reducing the energy needed to keep the body upright. However, these features provide less flexibility in knee and foot.
The valgus knee is an important adaptation that balances the body weight above the ankle during bipedal movement. The femur has a long neck that absorbs stress and accommodates for a larger pelvis. In elderly, the femur weakens through osteoporosis and hence locomotion can be greatly affected.
The S-shaped curve in the lumbar region allows the body to stand upright and absorbs shock. The upper limb is short and the lower limb is long with larger joints. The limbs provide more mechanical strength, stability and absorb stress.

Note:
Animals can exhibit obligate bipedalism or limited bipedalism. Limited bipedalism means using two legs only for certain activities like feeding, sitting or fighting. Examples include rats, raccoons, bears and beavers. The adaptation features of limited bipedalism vary greatly with that of obligate bipedalism. For instance, upper limbs are longer and lower limbs are smaller in limited biped animals but in obligate bipeds it is vice versa.