“Acanthodians are not at all shark-like in shape, for example they have diamond-shaped scales and spines in front of all the fins,” says Emma. “But they do have a cartilage skeleton, a shark-like ...

The exact number varies depending on the species. The only part of a shark's skeleton not made of cartilage is their teeth, which they're famous for. Since cartilage is softer than bone and teeth, it ...