Final answer:
The development of erect posture is significant as it leads to structural adaptations supporting the body's weight, and improvements in oxygen transport through a four-chambered heart and secondary palate. It enables efficient movement and increased metabolism necessary for terrestrial life.
Step-by-step explanation:
The development of erect posture in humans is significant for several reasons. It allows for the weight of the body to be supported on the limbs, which has led to the strengthening and ossification of the limbs and a more ossified vertebral column. As a consequence of erect posture, the axial skeleton of terrestrial tetrapods evolved to support the body's weight against gravity, leading to reduced strain through vertical motion of vertebrae rather than lateral flexion.
Associated with these structural changes are adaptations in the cardiovascular system, such as the four-chambered heart and secondary palate, which improve oxygen transport and separate the airway from the food passage, respectively. The development of a four-chambered heart is crucial for high metabolism and efficient oxygen delivery to the body, while a secondary palate helps with breathing while eating. Additionally, the evolutionary step towards erect posture demanded changes in the skeletal structure, such as the loss of direct attachment between the pectoral girdle and the head, allowing independent head movement.