Holly, a 13 year old female from the Internet asks on February 13, 1998,What is the difference between a dolphin and a porpoise?
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"Dolphin" usually refers to the specific group of small, toothed cetaceans in the family Delphinidae. There are over 30 species of true dolphins, including familiar species like the bottlenose, spinner, and spotted dolphins. Although the largest members of this group are commonly called whales because of their size, they are actually most closely related to other dolphins. The large dolphins include killer whales and pilot whales.
"Porpoise" refers to six species in the family Phocoenidae. All porpoises are relatively small by cetacean standards, measuring 7 feet (2 meters) or less as adults. Dolphins always have cone-shaped teeth, usually have a beak, and usually have a hooked or curved dorsal fin (some have no dorsal fin).
Porpoises always have spade-shaped teeth, never have a beak, and usually have a dorsal fin shaped like a triangle (some have no dorsal fin).
- From Masters of the Ocean Realm: Whales, Dolphins, and Porpoises. by John E. Heyning, (Seattle: University of Washington Press, 1995), p. 31.
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