Dolphins Essay

302 WordsNov 19, 20142 Pages
Dolphins are small members of the whale order, Cetacea. Although the terms dolphin and porpoise are sometimes used interchangeably to refer to any member of the group, biologists recognize three distinct families: the true porpoises, with six marine species; the river dolphins, with five freshwater species; and the true dolphins, with more than 30 marine species. The killer whales and pilot whales are closely related to the true dolphins and are included in the same family. Although they are similar in appearance, a dolphin is distinguished from a porpoise by its long, sharp snout that is flattened like a beak; a porpoise has a short, blunt snout. The teeth of dolphins are cone-shaped while those Dolphins and porpoises, often called simply "small whales," are mammals, not fishes, and are thus warm-blooded, keeping their body temperature nearly constant even when they are exposed to different environmental temperatures. The mothers provide milk for the young and nurse them for a year or more. Like other whales, dolphins have lungs and breathe through a single nostril called the blowhole located on top of the head. The blowhole is opened during their frequent trips to the surface to expel and inhale air. In contrast to some of the large whales, dolphins and porpoises have teeth, which they use to seize their food, consisting primarily of marine fishes and larger. Dolphins and porpoises have two flippers, fins that serve as forelimbs, and an upright triangular fin on the back. The tail is horizontal--to propel the animal in its lunges and dives--not perpendicular like the tails of fishes. Dolphins and porpoises are noted for being graceful swimmers, arcing through long, slow curves that bring the blowhole to the surface of the water and then expose the back fin as the animal dips

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