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Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea.Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the Globicephalinae (round-headed whales, which include the false killer whale and pilot whale).
Adult dolphins come to the water surface to breathe for 20 to 30 seconds before diving deep again, for two to eight minutes. Dolphin calves, with smaller lung capacities, surface twice as often as adults, staying underwater for one to three minutes. Adult dolphins rarely stay under water for more than four minutes.
Bottlenose dolphins can live for more than 40 years. Females typically live 5–10 years longer than males, with some females exceeding 60 years. [37] [38] [39] This extreme age is rare and less than 2% of all Bottlenose dolphins will live longer than 60 years. [40] Bottlenose dolphins can jump to a height of 6 metres (20 feet) in the air. [41]
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.
White-sided dolphins swim in groups of 10 to 100, and can often be seen bow-riding and doing somersaults. [6] [18] Members form a close-knit group and will often care for a sick or injured dolphin. Animals that live in such large social groups develop ways to keep in touch, with each dolphin identifying itself by a unique name-whistle.
In comparison to other dolphin species, the Atlantic spotted dolphin is medium-sized. Newborn calves are about 35–43 in (89–109 cm) long, while adults can reach a length of 2.26 m (7 ft 5 in) and a weight of 140 kg (310 lb) in males, and 2.29 m (7 ft 6 in) and 130 kg (290 lb) in females.
Hundreds of bottlenose dolphins live in captivity across the world, though exact numbers are hard to determine. [147] The dolphin "smile" makes them popular attractions, as this is a welcoming facial expression in humans; however, the smile is due to a lack of facial muscles and subsequent lack of facial expressions. [148]
An Atlantic white-sided dolphin off the coast of Cape Ann, Massachusetts. The Atlantic white-sided dolphin is a small delphinid. At birth, calves measure just over a meter long; adult males grow to about 2.8 m (9.2 ft), and females to about 2.5 m (8.2 ft), [3] weighing between 180–230 kg (400- 510 lb) once fully grown. [3]