Shark: The cartilaginous fish older than the dinosaurs

The shark is an "elder" of the ocean: older than the dinosaurs, it has patrolled the seas for over 400 million years. Across that vast span it has evolved an outstanding set of "sensing equipment", making it one of the ocean's most efficient predators. Let's meet it.

Its body

A shark's skeleton is unlike most fishes': instead of hard bone it is built from light cartilage. Cartilage is lighter and more flexible, letting a shark swim with less effort. Its skin is covered in tiny "dermal denticles" — scales that share an origin with teeth and feel as rough as sandpaper. Curiously, these denticles also reduce drag, helping the shark swim faster.

It also has a special "sixth sense": around its mouth and head are small pores called ampullae of Lorenzini, able to detect the faint electric fields given off by prey. So even if a prey animal hides in the sand out of sight, the shark can "feel" its heartbeat.

Where it lives and what it eats

Sharks are carnivores, eating fish, squid and crustaceans; larger species also prey on marine mammals such as seals. They sit at the top of the ocean food chain, helping keep the ecosystem in balance. There are many species, from small sharks under a metre to giants over ten metres long.

A note for grown-ups

You could talk with a child about how sharks are not only something to fear: they are a vital part of the ocean and many are threatened by overfishing. Helping a child understand the shark's situation is a fine way to build environmental awareness.