Whales are aquatic mammals of the order Cetacea, found in oceans worldwide. Adapted to an entirely aquatic life, they have a fish-like shape, nearly hairless skin, an insulating layer of blubber, and flipper-like forelimb. The tail is flattened horizontally and is used for propulsion. Surfacing to breathe, whales expel air through a dorsal blowhole. They have good vision and excellent hearing, and many species use echolocation for underwater navigation. Most whales travel in schools, often migrating thousands of miles. There are two major groups of whales, the toothed, which includeg the sperm whale (which DNA studies suggest is more closely related to baleen whales), killer whale, beluga (or white whale), and narwhal; and the toothless (or baleen), which include the blue, finback, gray, right, humpback, and minke whales. Species vary greatly in size and include the largest animal that has ever lived, the blue whale, up to 100 feet (30 meters) long and 150 tons. Commercial whaling has reduced all large species to endangered status. The intelligence and communication systems of the whale are subjects of scientific investigation.
