Sharks There are about 450 species of sharks with representatives in all the oceans of the world. They first appeared 400 million years ago, before reptiles, birds or mammals. They belong to a class of fish called the Chondrichthyes, in which their skeletons are made of cartilage rather than bone. They vary greatly in size and form. Some have flattened bodies as an adaptation to a lifestyle on the bottom of the seabed, such as the angel …showed first 75 words of 271 total…

…showed last 75 words of 271 total…sense and can detect electrical signals generated by prey. This makes them expert hunters and may also help them to navigate through the water. Their sense of smell is particularly good and many sharks will gather from miles around to congregate on a bloody kill. Many sharks are endangered because of humans. They are hunted for their meat, skin, fins, liver oil and for sport, and they are often caught and killed in fishing nets.