What is the evolutionary innovation associated with cartilaginous fish such as a shark?

The primary evolutionary innovation associated with cartilaginous fish, like sharks, is the development of a skeleton made of cartilage instead of bone. This adaptation allows for greater flexibility and lighter body structures, enabling more efficient movement in water. Additionally, their unique dental structure, including continuously replacing teeth, enhances their predatory capabilities. These features have contributed to their success as apex predators in marine ecosystems.