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- Dolphins are famous for their antics in and out of water,
especially the leap and their willingness to engage with
Dolphins are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). They are related to the Indohyus, an extinct chevrotain-like ungulate, from which they split approximately 48 million years ago.
The primitive cetaceans, or archaeocetes, first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later.
Dolphins have torpedo shaped bodies with generally non-flexible necks, limbs modified into flippers, non-existent external ear flaps, a tail fin, and bulbous heads. Dolphin skulls have small eye orbits, long snouts, and eyes placed on the sides of its head. Dolphins range in size from the 1.7 metres (5.6 ft) long and 50 kilograms (110 lb) Maui's dolphin to the 9.5 metres (31 ft) and 10 metric tons (11 short tons) killer whale. Overall, however, they tend to be dwarfed by other Cetartiodactyls. Several species have female-biased sexual dimorphism, with the females being larger than the males.
Dolphins have conical teeth, as opposed to porpoises' spade-shaped teeth. These conical teeth are used to catch swift prey such as
fish, squid or large mammals, such as
Breathing involves expelling stale air from their blowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs, however this only occurs in the polar regions of the oceans. Dolphins have rather small, unidentifiable spouts.
All dolphins have a thick layer of blubber, thickness varying on
climate. This blubber can help with buoyancy, protection to some extent as predators would have a hard time getting through a thick layer of fat, and
energy for leaner times; the primary usage for blubber is insulation from the harsh climate. Calves, generally, are born with a thin layer of blubber, which develops at different paces depending on the habitat.
Dolphins have a two-chambered stomach that is similar in structure to terrestrial carnivores. They have fundic and pyloric chambers.
Dolphins' reproductive organs are located inside the body, with genital slits on the ventral (belly) side. Males have two slits, one concealing the dolphin penis and one further behind for the anus. Females have one genital slit, housing the vagina and the anus, with a mammary slit on either side.
Dolphins range in size from the 1.7 m (5.6 ft) long and 50 kg (110 lb) Maui's dolphin to the 9.5 m (31 ft) and 10 t (11 short tons) killer whale. Several species exhibit sexual dimorphism, in that 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, some dolphins can travel at 55.5 km/h (34.5 mph). Dolphins use their conical shaped teeth to capture fast moving prey. They have well-developed hearing which is adapted for both air and water and 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
Although dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, like 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 like 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 occasionally feature in literature and film, as in the film series
Willy. Dolphins are sometimes kept in captivity and trained to perform tricks. The most common dolphin species kept is the bottlenose dolphin, while there are around 60 captive
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