Sharks are fish that live in all the world's oceans. A few species also live in rivers. They belong to the group of predatory fish: Most eat fish and other marine animals.
When sharks swim on the surface of the water, they can be recognized by their triangular dorsal fin that sticks out of the water. Sharks have been swimming through the ocean as far back as 400 million years ago, so they are one of the oldest species in the world.
The dwarf shark is the smallest shark at 25 centimeters long, while the whale shark is the longest at 14 meters. The whale shark is also the heaviest shark: at up to twelve tons, it weighs as much as ten small cars. In total, there are about 500 species of sharks.
Sharks have a special set of teeth: behind the first row of teeth, more rows grow. Then, when teeth fall out in a fight with other animals, the next teeth move up. In this way, a shark "consumes" up to 30,000 teeth in its lifetime.
The shark's skin is not made of normal scales, but of the same material as the teeth. "Skin teeth" is what these scales are called. From the head to the tail fin this skin feels quite smooth, the other way around it feels rough.