Sharks don’t have bones.
All sharks have cartilage for their skeleton rather than bones. This is very different from humans and most types of land animals. Having this cartilage though is what allows them to move at unbelievable speeds through the water.1
Unlike most fish, sharks possess skeletons made completely of cartilage. Cartilage is a softer, more flexible tissue than bone. The reason you can bend your ear or tip of your nose is because it’s supported by cartilage. Most bones in our body are formed by cartilage precursors that later become calcified to form the hard skeletal tissue we know as bone. Sharks actually do form some types of calcified tissues, such as their teeth, so they do have the ability to form bone. Then why don’t they form bone for their whole skeleton? Well, sharks evolved from bony ancestors so in fact they actually evolved to not produce a bony skeleton. There are several ideas why this may have occurred. One thought is that the evolution of a cartilaginous skeleton gives sharks a more flexible, maneuverable body, making them extremely well adapted for a variety of swimming modes. A flexible body is also helpful for moving around complex habitats and tucking into small spaces and crevices.2
Source1: sharks-world.com
Source2: CCMR