Final answer:
It is true that in bipeds, the lumbar vertebrae are enlarged to efficiently bear weight. They are designed to provide stability and support for the body's weight in an upright posture, with structural adaptations that enable efficient weight transfer and upright mobility.
Step-by-step explanation:
The question asks whether it is true or false that in bipeds, the lumbar vertebrae are enlarged to more efficiently bear weight. The answer is true. The lumbar vertebrae are indeed characterized by a large size and thickness of the vertebral body, which helps carry the greatest amount of body weight. Due to the upright stance of bipeds, there are different functional demands on the lumbar vertebrae compared to other vertebrates. The short transverse processes and the blunt spinous process, along with large articular processes, contribute to the strength and stability required to support the body's weight and maintain an upright posture.
In bipedal locomotion, the efficient weight transfer from the vertebral column through the pelvic girdle and into the lower limbs is crucial. The lumbar region's vertebrae, numbered L1-L5, provide a strong foundation for the upper body while allowing for mobility of the lower limbs. Evolutionary changes such as the ossification of the limbs, development of spinal curves, and the alignment of the lower limb structure, including the femur at a valgus angle, all support the lumbar vertebrae in sustaining the weight of an upright body.