All About Sharks

Graceful, fast-moving animals with rows of razor-sharp teeth - that's how most people describe sharks.

There are many sharks like this, but there are also many other kinds of sharks. In fact, there are more than 350 species of sharks!

What Do People Think About Sharks?

Most people only ever hear about a sharks when there is a shark attack. Shark attacks are rare, but sharks have never really received good publicity. Fortunately, attitudes are changing,  especially as we learn more about them and begin to understand these amazing creatures.

What a history!

Sharks existed long before there were dinosaurs-the oldest known remains of a shark are 420 million years old! These remains are called fossils. Usually only fossil teeth and scales are found.

Prehistoric Sharks

The cladoselache (clad-oh-suh-LOCK-y) was a shark that swam in seas that coveren eastern United States 400 million years ago. It was about 1 metre (3 feet) long and had a tail like that of a mako shark, a fast-swimming species that exists today.

Over millions of years the species of sharks that exist today first appeared about 100 million
years ago. Fossil teeth from the largest predatory shark that ever existed have been found
which are over 60 million years old. The great white shark is related to this ancient animal.

Different types of sharks

Scientist place 350 or so species of sharks in to 30 family groups. Each of these groups has features that are easily recognised. For example, the sawsharks have long, flat snouts lined with sharp teeth rather like a saw. Hammerheads have distinctively hammer-shaped heads. Great whites and mako sharks are fast swimmers with stout cylindrical bodies.

All Shapes And Sizes

The Megamouth (mighty mouth) shark is one of the biggest sharks. Megamouths live in the deep waters of the ocean and perhaps this is why only a few specimen have ever been found. They feed on Plankton, tiny animals and plants, which they filter from the seawater. The smallest sharks are the pygmy sharks. They belong to the dogfish shark group. Pygmy sharks may only grow to a length of15-20 centimetres (6-8 inches)

The outside of a shark

A shark's sleek shape is easily recognised, although sharks that live on sea floor have flattened appearance.

Recognising A Shark

A shark's body is very flexible, allowing it to twist and turn as it chases its prey, or escapes a predator-after all, sharks can be prey themselves, especially when they are young. A shark's skeleton has cartilage instead of bone. Cartilage is light and elastic, so it bends easily. Give your nose a little wobble from side to side; it is the cartilage in the end of your nose that is bending.

The inside story

Features of an animal that help it survive in its envirement are called adaptions. Sharks have many adaptions. For example, their streamlined shape helps them to move through water. Inside a shark's body there are more adaptions.

Brains...

It was once believed that sharks were simply "mindless reating machines" with very small brains. However, studies have shown that the size of a shark's brain, in comparison to its body size, is similar to that of many mammals and birds.

...And Brawn!

Generally, sharks have two types of muscle-red muscle and white muscle. Red muscle is just below the skin and is used when a shark cruises slowly, perhaps for hours. White muscle beneath the red muscle layer is used for rapid movement, such as when the shark chases prey.

Shark Senses

Finding food in the vastness of the sea requires keen senses. Sharks are successful predators because they are able to detect prey which is often hidden from view or some distance away.

Seeing Things

Fast-moving sharks have excellent vision. In poor light these sharks' pupils widen to let more light into the eyes. They also have mirror -like plates at the back of their eyes. These reflect light back into the eyes and improve the shark's vision. At night shark's eyes shine, like a cat's eyes, because of these plates. Bottom-dwelling sharks have small eyes and rely more on other senses to detect prey.

Electro-sense

Sharks not only have senses of touch, sight, hearing, smell and taste, they can also sense elevtricity.

Ampullae Of Lorenzini

Lying in tiny holes on the skin around the shark's head are small electrical receptors called ampullae of Lorenzini. Receptors are part of the nerve system in the shark's body and they pick up the tiny electrical impulses made by the muscles of fish. A shark hunting for food hidden in the sand of the sea floor, or in darkness, makes good use of this electro-sense. The ampullae of Lorenzini may also give the shark a sense of direction, similar to the way a compass works.