Sharks

SCIENTIFIC CLASSIFICATION:

TIME PERIOD:

They are presents to date.

HABITAT:

Sharks are those feared predators of the sea. There are about 350 species of fish under sharks. They are found around the world, but they are most common in warm seas.

DESCRIPTION:

Sharks vary widely. The largest shark - the whale shark is over 12 metres and more than 10 tons. The smallest are not more than 20 cenimetres and 40 grams in weight. Some dive to the deepest of depths and some live near the surface. Some live near the coast, and still others deep in the ocean.

Sharks eat meat - all of them. Most eat fish, some eat other sharks. Each shark faces danger from a larger one. They have unique ways to finish off their prey. Some crush them, most eat them whole or in morsels. There are report of man eating sharks, but this is rare. They usually go for smaller prey.

The body of a shark

Sharks have a body made of cartilage. The material is tough and elastic. They have a streamlined body. This streamlined shape aids in swimming. Angel sharks, which live near the ocean bottom, have a flat body similar to that of skates and rays.

Sharks do not reproduce as much as other fish do, they have less pups per litter. They do not care for the young, they may even eat them. The eggs of a shark is fertilized inside the body of the female. In most species, the eggs hatch, and then the pups are born. But more than 30 lay the eggs.

Sharks can travel very fast. The tails and fins help the shark attain great speeds. The tail is usually crescent shaped in the fastest sharks. The upper side is generally longer.

Sharks do not have a air bag. The liver of a shark, instead, is filled with water. The oil is lighter and prevents it from sinking, but the shark must constantly swim.

Teeth and scales. A shark's mouth is on the underside of the head among all species except the angel, megamouth, whale, and wobbegong sharks. The mouth of these sharks is at the front of the head. A shark has several rows of teeth. New teeth replace the rows of old teeth regularly--as often as every one to two weeks. Some sharks have molar like grinding teeth. Others have razor like cutting teeth, and still others have pointed teeth. Some people believe that sharks must turn over on their back to bite, but this is not true.

The gills of sharks have no covering, they are externally visible. They have five or more gill slits. These help the water pass out after the sharks gills absorb oxygen. Sharks cannot pump water over the gills, so most rely on swimming force to make water pass over their gills and mouth.

Sharks can hear low pitched sounds well. The eyes of a shark can see well even in dim light. Sharks also can see a bit in colour. Such senses help the shark in successfully hunting its prey. Sharks can feel even small electric fields. They can catch fish based on the little electrical field produced by their gills.

ITS PART IN EVOLUTION TABLE:

It has no special role in the evolutionary table. It comes under cartilaginous fish