Sharks are well known for their roles in pop culture, their fear factor, and their ability to swim non-stop through the ocean. But what many people don’t realize is that sharks do not have bones in the same way that humans or other fish have. Instead, how many bones does a shark have a cartilage skeleton that allows them to be incredibly flexible and fast in the water? Today’s WONDER of the day was inspired by Maya from Fairfax, VA.

Shark jaws that are mounted as ornaments look like bone but they are actually boneless. This is because they are made of cartilage that has dried out. Sharks actually have teeth, though, which are constantly growing and being replaced throughout their lives. This means that a single shark can have between 50 and 300 teeth at various stages of its life.

The skeletal structure of sharks is formed from a series of cartilage discs stacked together. The discs are reinforced by dentine plates called dermal denticles and are covered with small, hardened spicules. Sharks’ cartilage skeletons allow them to move rapidly in the water and make sharp turns, as needed for hunting prey or evading predators. Cartilage is also lighter and more flexible than bone, so it helps them conserve energy as they swim to pursue their prey or make quick turns to escape a predator.

Another advantage of sharks’ cartilaginous skeleton is that they can regrow their cartilage if it becomes damaged. This has helped them thrive as apex ocean predators for millions of years. Sharks also have a special blood cell-producing system that uses their spleen, gill arches, and Leydig’s organ to produce red blood cells. This system is called hematogenesis.