Final answer:
The differences in the pelvis of a biped compared to a quadruped are necessary to facilitate successful bipedal locomotion. These differences include the angling of the femur, spinal curves, and the evolution of the foot arch and big toe.
Step-by-step explanation:
One of the key differences between the pelvis of a biped (an animal that walks on two legs) compared to a quadruped (an animal that walks on four legs) is the angling of the femur. In bipeds, the femur is angled inward, creating a valgus angle, which helps position the knees and feet under the center of the pelvis. This anatomical change is essential for successful bipedal locomotion. Additionally, bipedal hominins (early humans) have evolved spinal curves that allow the hips to balance the weight of the upper body. The evolution of the arch in the foot and the realignment of the big toe are also important for transmitting weight during bipedal walking.