Final answer:
The pelvic girdle underwent two adaptations to resist gravity: increased size and strength, and increased immobility.
Step-by-step explanation:
The pelvic and pectoral girdles underwent adaptations to help resist gravity when vertebrates moved onto land. Two adaptations of the pelvic girdle are:
- Increased size and strength: The pelvic girdle became larger and stronger in order to support the weight of the body on land. This provided stability and helped resist bending caused by gravity.
- Increased immobility: The bones of the pelvic girdle are strongly united to each other, forming a largely immobile, weight-bearing structure. This provides a strong foundation for the upper body as it rests on top of the mobile lower limbs.