A cetacean is any member of the order Cetacea, which includes the whales, dolphins, and porpoises. These aquatic, air-breathing, fish-like mammals have streamlined bodies, a pair of front flippers, and horizontal tail flukes that operate with an up-and-down stroke making speeds of 45–55 kilometers per hour possible. Their bodies are insulated by a thick layer of blubber. About 78 species of cetacean have been identified. Their length varies from about 1.5 meters (4.9 feet) to more than 30 meters (100 feet), and their weight from about 36 kilograms (80 pounds) to 100 tonnes.
Cetaceans are divided into two suborders, or main groups:
There are 11 species of baleen whales and 67 species of toothed whales.
Usage of the names whale, dolphin, and porpoise can be confusing. As the above classification indicates, all cetaceans can correctly be called whales; specifically, all dolphins and porpoises can be called toothed whales. However, it is common practise to call any cetacean that as an adult can reach more than about 9 feet in length a whale, and anything smaller than this a dolphin or a porpoise. Dolphins and porpoises can be distinguished in four ways:
There are six species of porpoise, all members of the family Phocoenidae: the harbor porpoise, the vaquita, the spectacled porpoise, Burmeister's porpoise, the finless porpoise, and Dall's porpoise.
For more on some specific types of whale, see:
Cetaceans have long been noted for their intelligent and sometimes apparently compassionate behavior (see dolphins as a form of alien intelligence). More recently, it has become clear that they produce an extraordinary variety of complex vocalizations across a wide frequency range, which in addition to uses such as echo-location and mating rituals, may serve as a sophisticated form of communication (see songs of humpback whales).
"By 2100 A.D. on Earth, three species of cetacean
had been recognized as intelligent and admitted to the United Nations.
Their lawsuit against the former whaling nations had not been resolved,
and in fact never was. The cetaceans enjoyed the legal gymnastics too
much ever to end it."
– Larry Niven, "At the Bottom of a Hole" (1966)