Caption: Whale shark and a human

There are more than 350 different kinds of sharks swimming in the oceans. Sharks are fish. Sharks have lived in Earth's oceans for a very long time. Millions of years before there were dinosaurs, there were sharks. Sharks come in all sizes. The dwarf shark only grows to be about six inches long. The whale shark can be sixty feet long!

Unlike most bony fish, sharks do not have hard bones inside their bodies. Instead, sharks' skeletons are made of cartilage, like the end of your nose. Most fish have smooth scales covering their bodies. Sharks' bodies are covered with denticles. Denticles, also called placoid scales, are like little sharp teeth. This gives sharks' skin a rough texture, like sandpaper. In fact, before sandpaper was invented, people used shark skin to smooth wood.

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