Which of the following adaptations is NOT associated with bipedalism?

The adaptation that is not associated with bipedalism is the long and narrow pelvis. In the context of bipedalism, the pelvis undergoes significant changes to accommodate upright walking. Unlike a long and narrow pelvis, which would be more suited to a quadrupedal or arboreal lifestyle, the pelvis in bipedal organisms is typically broader and shorter. This allows for better support of internal organs while walking on two legs and provides an efficient structure for the attachment of gluteal muscles, which are crucial for maintaining balance and propulsion during bipedal locomotion.

In contrast, the other adaptations mentioned have direct relevance to bipedalism. For example, an expansion of the brain is associated with higher cognitive functions that may have evolved alongside the development of bipedalism. A reduction in canine size is often linked to changes in social dynamics and dietary needs as hominins adapted to different environments. Modifications in the postcranial skeleton, including changes in limb proportions and joint structure, directly facilitate bipedal movement and enhance locomotion efficiency. Hence, the characteristics of the pelvis play a crucial role in successful bipedalism, making a long and narrow pelvis an unsuitable adaptation for this mode of locomotion.