Why Don't Sharks Have Bones?
Sharks are completely boneless. Instead of bones, sharks have skeletons made up of cartilage. A cartilage skeleton has its advantages: it is flexible, durable and light, and also heals faster than bone. That said, once a shark is out of water, the cartilage skeleton works against them. They can easily be crushed by their own body weight on land -- because sharks lack rib cages, their weight isn't supported out of water, and their bodies would collapse over time.