Researchers do know that sharks and rays are some of Earth's oldest fish. Once, more than 400 million years ago, the two groups shared a common ancestor that swam through the planet's oceans long before the first dinosaur appeared. Today, to the untrained eye, that common origin isn't obvious, because most sharks and rays look so different from one another. But the fish are, in fact, relatives with structural similarities. Some sharks are reputed to be able to detect minute quantities of substances such as blood in water from several hundred feet away.
Some sharks grow to be only a foot long.
Despite its size, the Whale shark feeds on some of the ocean's smallest life, the tiny plants and crustaceans that drift near the surface. In fact, fewer than 50 shark species grow to be longer than six feet, and most rarely reach three feet long. Sharks also vary in lifestyle. Sleek Mako sharks, for instance, may spend their days cruising the seas at up to 40 miles per hour, hunting fish and occasionally launching themselves into the air with acrobatic leaps. Angelsharks, however, prefer a more sedate existence.