Did you know that sharks don’t have true scales?

Instead, their skin is covered in thousands of tiny dermal denticles, which literally means “tiny skin teeth”. The spines of these denticles point towards the tail, which makes the shark’s skin feel smooth if you brush your hand across its skin towards the tail, but gives it a sandpaper-like texture if you brush towards the shark’s head.

These v-shaped denticles are closely spaced together. They are made of an inner pulp cavity that contains blood vessels, nerves, and connective tissue; and an outside layer of dentine made of a mineral called apatite. In contrast to scaled fish, whose scales can grow to be pretty large, dermal denticles stop growing once they reach a certain size, so as the shark’s body grows, it also grows more dermal denticles in order to keep its skin covered!

So why do sharks have these tiny teeth all over their skin? There are a couple good reasons. Differently sized denticles seem to serve different functions. Smaller, thinner denticles can reduce surface drag, helping the shark swim faster and more stealthily through the ocean. These tend to be found on the fins and near the gills. Larger, thicker denticles are more protective, providing the shark with a layer of armor that can keep them safer from predators and ectoparasites.

When denticles fall off, they are sometimes preserved at the bottom of reefs. Scientists can retrieve these denticles and identify the species of shark that the denticles came from. This allows us to study shark species distribution, as well as how human activities have impacted those species and their environments.

Check out these pictures- can you identify the species of shark based on the shape of their dermal denticles?