Sharks have lived in the ocean for over 400 million years, surviving 5 mass extinctions. Including the one that wiped out the dinosaurs.

How? Because they're so perfectly suited to their environment:


Sharks have a skeleton made of cartilage, rather than bone. This is the same stuff as human noses and ears. It's light and flexible, so helps them move quickly through the water. Which is very helpful when trying to catch fast swimming prey.

Scientists can tell the age of a shark by counting the rings on their backbone!


If you were to stroke a shark from head to tail, the skin would feel smooth. But if you stoked the other way it'd be rough. Like sandpaper. That's because sharks are covered with millions of tiny teeth-like scales, known as denticles. These point backwards helping them swim faster by reducing water resistance. As sharks grow they shed their denticles, replacing them with larger ones.


Sharks have several rows of teeth. As the front rows wear out, new rows move in from behind to replace them. This ensures they always have a full set of razor sharp teeth. Sharks can shed thousands of teeth in their lifetime.

Different sharks have different shaped teeth depending on what they eat. Those that eat shellfish, such as crabs, have flat crushing teeth to crunch through shells. Whereas those that eat fish have sharp pointed teeth for holding their slippery prey. Basking Sharks have tiny teeth but they don't use these to eat. Instead they filter tiny plants and animals from the water before it passes through their gills.


All fish have fins that help them balance and move in the water. But sharks are different to other fish because their fins don't fold.

  • Dorsal Fin - keeps them steady and upright.

  • Pectoral Fins - 2 large side fins act like aeroplane wings. Water flows underneath lifting them up.

  • Tail - propels them through the water. 

Different sharks have different shaped tails depending on how they live. The Shortfin Mako has a crescent-shaped symmetrical tail that enables them to swim very fast. Whereas the top part of a Zebra Shark's tail is very long, allowing them to rest on the seabed. Thresher sharks have an extremely long, whip-like tail, which they use to stun their prey.


Most sharks have 5 pairs of gills. But some have 6 or 7. They use these to breathe.

As they swim, water enters their mouth and passes out through their gills. Tiny blood vessels near the gills absorb oxygen in the water, which is then carried around the body. This means that a shark has to keep moving to breathe. Yet there are exceptions. Some species are able to rest by sucking water into their mouth and pumping it across their gills.


Bony fish are able to control their level in the water using an organ known as a swim bladder. This stops them from sinking or floating. But sharks don't have swim bladders, so have to rely on other adaptations instead. Their light cartilage skeleton helps. As does a large oily liver. Both make the shark lighter, helping to stop them from sinking. Water movement under their fins also provides lift.


Sharks have 2 types of muscle (red and white) that allow them to move.

  1. RED MUSCLE - lies just under their skin. Using energy from stored fats this muscle enables them to swim slowly for a long time.

  2. WHITE MUSCLE - lies under the red muscle. This relies on energy from the breakdown of sugars. And makes it possible for a shark to make short fast sprints, when catching prey or fleeing from danger.


Most fish are cold blooded. So, their body temperature is the same as the surrounding water. Yet some sharks, such as the White Shark, can warm their blood. Their body temperature can be up to 10ºC higher than the surrounding water. How amazing is that?!

Related Links:

Shark Senses

Top Sharks - find out which shark is the fastest, largest, weirdest, and more...

Sharks in Danger - find out about the biggest threats currently facing sharks

Take Action - find out how you can help sharks