Dolphin
A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the brackish dolphins), and possibly extinct Lipotidae (baiji or Chinese river dolphin). There are 40 extant species named as dolphins.
For other uses, see Dolphin (disambiguation).
Dolphins range in size from the 1.7-metre-long (5 ft 7 in) and 50-kilogram (110-pound) Maui's dolphin to the 9.5 m (31 ft) and 10-tonne (11-short-ton) orca. Various species of dolphins exhibit sexual dimorphism where the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, they are faster; some dolphins can briefly travel at speeds of 29 kilometres per hour (18 mph) or leap about 9 metres (30 ft).[1] Dolphins use their conical teeth to capture fast-moving prey. They have well-developed hearing which is adapted for both air and water. It is so well developed that some can survive even if they are blind. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water.
Dolphins are widespread. Most species prefer the warm waters of the tropic zones, but some, such as the right whale dolphin, prefer colder climates. Dolphins feed largely on fish and squid, but a few, such as the orca, feed on large mammals such as seals. Male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively long period of time. Dolphins produce a variety of vocalizations, usually in the form of clicks and whistles.
Dolphins are sometimes hunted in places such as Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they also face threats from bycatch, habitat loss, and marine pollution. Dolphins have been depicted in various cultures worldwide. Dolphins are sometimes kept in captivity and trained to perform tricks. The most common dolphin species in captivity is the bottlenose dolphin, while there are around 60 orcas in captivity.
Etymology
The name is originally from Greek δελφίς (delphís), "dolphin",[2] which was related to the Greek δελφύς (delphus), "womb".[2] The animal's name can therefore be interpreted as meaning "a 'fish' with a womb".[3] The name was transmitted via the Latin delphinus[4] (the romanization of the later Greek δελφῖνος – delphinos[2]), which in Medieval Latin became dolfinus and in Old French daulphin, which reintroduced the ph into the word dolphin. The term mereswine ("sea pig") has also historically been used.
The term dolphin can be used to refer to most species in the family Delphinidae (oceanic dolphins) and the river dolphin families of Iniidae (South American river dolphins), Pontoporiidae (La Plata dolphin), Lipotidae (Yangtze river dolphin) and Platanistidae (Ganges river dolphin and Indus river dolphin).[5][6] Meanwhile, the mahi-mahi fish is called the dolphinfish.[7] In common usage, the term whale is used only for the larger cetacean species,[8] while the smaller ones with a beaked or longer nose are considered dolphins.[9] The name dolphin is used casually as a synonym for bottlenose dolphin, the most common and familiar species of dolphin.[10] There are six species of dolphins commonly thought of as whales, collectively known as blackfish: the orca, the melon-headed whale, the pygmy killer whale, the false killer whale, and the two species of pilot whales, all of which are classified under the family Delphinidae and qualify as dolphins.[11] Although the terms dolphin and porpoise are sometimes used interchangeably, porpoise usually refers to the Phocoenidae family, which have a shorter beak and spade-shaped teeth and differ in their behavior.[10]
A group of dolphins is called a school or a pod. Male dolphins are called bulls, females are called cows and young dolphins are called calves.[12]
Hybridization
In 1933, three hybrid dolphins beached off the Irish coast; they were hybrids between Risso's and bottlenose dolphins.[13] This mating was later repeated in captivity, producing a hybrid calf. In captivity, a bottlenose and a rough-toothed dolphin produced hybrid offspring.[14] A common-bottlenose hybrid lives at SeaWorld California.[15] Other dolphin hybrids live in captivity around the world or have been reported in the wild, such as a bottlenose-Atlantic spotted hybrid.[16] The best known hybrid is the wholphin, a false killer whale-bottlenose dolphin hybrid. The wolphin is a fertile hybrid. Two wolphins currently live at the Sea Life Park in Hawaii; the first was born in 1985 from a male false killer whale and a female bottlenose. Wolphins have also been observed in the wild.[17]
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