Whale, large mammal that lives its entire life in the water. Whales have a fishlike body; however, their tail fins, called flukes, are horizontal rather than vertical, and they have paddlelike front limbs, called flippers. Their skin is smooth and glossy and, depending on the species, may be black, white, or a variety of colors and patterns. Beneath the skin is a thick layer of fat, called blubber, which provides insulation and serves as a source of stored energy.
Whales resemble fish in many ways, but they are not fish. Fish are cold-blooded and breathe underwater using gills; whales, on the other hand, maintain a warm and constant body temperature of about 37°C (about 99°F) and breathe air with lungs. Unlike fish, which move their vertical tail fins from side to side when they swim, whales move their horizontal tail fins up and down to propel themselves through the water.
Whales belong to the mammalian order Cetacea. Scientists classify whales into two groups. One group, known as the Odontoceti, or toothed whales, have jaws lined with pointed teeth that they use in hunting fish, squid, and other prey. Toothed whales also include dolphins and porpoises. The other whale group, called the Mysticeti, or baleen whales, lack teeth. These whales use giant, flexible combs of a material called baleen to filter small fish and tiny crustaceans from the water.
Whales are found in all the world’s oceans and even in a few rivers. One species of dolphin, the pink river dolphin, lives only in the Amazon River and its larger tributaries. Some whales, including the blue, fin, humpback, and gray, undertake some of the longest migrations in the animal kingdom, traveling between the tropics in winter and subpolar waters in summer. Other whales do not migrate long distances or, like the killer whales, wander without specific migratory routes
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