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Dolphin

2007 Schools Wikipedia Selection. Related subjects: Mammals

   How to read a taxoboxDolphin

                    Fossil range: Early Miocene - Recent

   Bottlenose Dolphin breaching in the bow wave of a boat
   Bottlenose Dolphin breaching in the bow wave of a boat
                 Scientific classification

   Kingdom:  Animalia
   Phylum:   Chordata
   Class:    Mammalia
   Order:    Cetacea
   Suborder: Odontoceti
   Family:   Delphinidae and Platanistoidea
             Gray, 1821

                                   Genera

   See article below.

   Dolphins are aquatic mammals which are closely related to whales and
   porpoises. There are almost forty species of dolphin in seventeen
   genera. They vary in size from 1.2 metres (4 ft) and 40 kilograms (88
   lb) ( Maui's Dolphin), up to 9.5 m (30 ft) and ten tonnes (the Orca).
   They are found worldwide, mostly in the shallower seas of the
   continental shelves, and are carnivores, mostly eating fish and squid.
   The family Delphinidae is the largest in the Cetacea, and relatively
   recent: dolphins evolved about ten million years ago, during the
   Miocene. Dolphins are considered to be amongst the most intelligent of
   animals and their often friendly appearance and seemingly playful
   attitude have made them popular in human culture.

Origin of the name

   The name is from Ancient Greek δελφίς delphis meaning "with a womb"
   which can be interpreted as meaning "a 'fish' with a womb".

   The word is used in a few different ways. It can mean:
     * Any member of the family Delphinidae (oceanic dolphins),
     * Any member of the families Delphinidae and Platanistoidea (oceanic
       and river dolphins),
     * Any member of the suborder Odontoceti (toothed whales; these
       include the above families and some others),
     * Used casually as a synonym for Bottlenose Dolphin, the most common
       and familiar species of dolphin.

   In this article, the second definition is used. Porpoises (suborder
   Odontoceti, family Phocoenidae) are thus not dolphins in this sense.
   Orcas and some closely related species belong to the Delphinidae family
   and therefore qualify as dolphins, even though they are called whales
   in common language. A group of dolphins can be called a "school" or a
   "pod".

Taxonomy

   Common Dolphin
   Common Dolphin
   Bottlenose Dolphin
   Bottlenose Dolphin
   Spotted Dolphin
   Spotted Dolphin
   Commerson's Dolphin
   Commerson's Dolphin
   Dusky Dolphin
   Dusky Dolphin
   Killer Whales, also known as Orcas
   Killer Whales, also known as Orcas
   The Boto, or Amazon River Dolphin
   The Boto, or Amazon River Dolphin
     * Suborder Odontoceti, toothed whales
          + Family Delphinidae, oceanic Dolphins
               o Genus Delphinus
                    # Long-Beaked Common Dolphin, Delphinus capensis
                    # Short-Beaked Common Dolphin, Delphinus delphis
               o Genus Tursiops
                    # Bottlenose Dolphin, Tursiops truncatus
                    # Indo-Pacific Bottlenose Dolphin, Tursiops aduncus
               o Genus Lissodelphis
                    # Northern Rightwhale Dolphin, Lissodelphis borealis
                    # Southern Rightwhale Dolphin, Lissiodelphis peronii
               o Genus Sotalia
                    # Tucuxi, Sotalia fluviatilis
               o Genus Sousa
                    # Indo-Pacific Hump-backed Dolphin, Sousa chinensis
                         @ Chinese White Dolphin (the Chinese variant),
                           Sousa chinensis chinensis
                    # Atlantic Humpbacked Dolphin, Sousa teuszii
               o Genus Stenella
                    # Atlantic Spotted Dolphin, Stenella frontalis
                    # Clymene Dolphin, Stenella clymene
                    # Pantropical Spotted Dolphin, Stenella attenuata
                    # Spinner Dolphin, Stenella longirostris
                    # Striped Dolphin, Stenella coeruleoalba
               o Genus Steno
                    # Rough-Toothed Dolphin, Steno bredanensis
               o Genus Cephalorynchus
                    # Chilean Dolphin, Cephalorhynchus eutropia
                    # Commerson's Dolphin, Cephalorhynchus commersonii
                    # Heaviside's Dolphin, Cephalorhynchus heavisidii
                    # Hector's Dolphin, Cephalorhynchus hectori
               o Genus Grampus
                    # Risso's Dolphin, Grampus griseus
               o Genus Lagenodelphis
                    # Fraser's Dolphin, Lagenodelphis hosei
               o Genus Lagenorhyncus
                    # Atlantic White-Sided Dolphin, Lagenorhynchus acutus
                    # Dusky Dolphin, Lagenorhynchus obscurus
                    # Hourglass Dolphin, Lagenorhynchus cruciger
                    # Pacific White-Sided Dolphin, Lagenorhynchus
                      obliquidens
                    # Peale's Dolphin, Lagenorhynchus australis
                    # White-Beaked Dolphin, Lagenorhynchus albirostris
               o Genus Orcaella
                    # Australian Snubfin Dolphin, Orcaella heinsohni
                    # Irrawaddy Dolphin, Orcaella brevirostris
               o Genus Peponocephala
                    # Melon-headed Whale, Peponocephala electra
               o Genus Orcinus
                    # Killer Whale, Orcinus orca
               o Genus Feresa
                    # Pygmy Killer Whale, Feresa attenuata
               o Genus Pseudorca
                    # False Killer Whale, Pseudorca crassidens
               o Genus Globicephala
                    # Long-finned Pilot Whale, Globicephala melas
                    # Short-finned Pilot Whale, Globicephala macrorhynchus
          + Family Platanistoidea, River Dolphins
               o Genus Inia
                    # Boto (Amazon River Dolphin), Inia geoffrensis
               o Genus Lipotes
                    # Chinese River Dolphin (Baiji), Lipotes vexillifer
               o Genus Platanista
                    # Ganges River Dolphin, Platanista gangetica
                    # Indus River Dolphin, Platanista minor
               o Genus Pontoporia
                    # La Plata Dolphin (Franciscana), Pontoporia
                      blainvillei

   Six species in the family Delphinidae are commonly called "whales" but
   are strictly speaking dolphins. They are sometimes called "blackfish".
     * Melon-headed Whale, Peponocephala electra
     * Killer Whale, Orcinus orca
     * Pygmy Killer Whale, Feresa attenuata
     * False Killer Whale, Psudorca crassidens
     * Long-finned Pilot Whale, Globicephala melas
     * Short-finned Pilot Whale, Globicephala macrorhynchus

Hybrid dolphins

   In 1933, three abnormal dolphins were beached off the Irish coast;
   these appeared to be hybrids between Risso's Dolphin and the Bottlenose
   Dolphin. This mating has since been repeated in captivity and a hybrid
   calf was born. In captivity, a Bottlenose Dolphin and a Rough-toothed
   Dolphin produced hybrid offspring. A Common-Bottlenose hybrid lives at
   SeaWorld California. Various other dolphin hybrids have also been
   reported in the wild, such as a Bottlenose-Atlantic Spotted hybrid. The
   best known hybrid however is the Wolphin, a False Killer
   Whale-Bottlenose Dolphin hybrid. The Wolphin is a fertile hybrid, and
   two such Wolphins currently live at the Sea Life Park in Hawaii, the
   first having been born in 1985 from a male False Killer Whale and a
   female Bottlenose. Wolphins have also been observed in the wild.

Evolution and anatomy

Evolution

   Dolphins, along with whales and porpoises, are thought to be
   descendants of terrestrial mammals, most likely of the Artiodactyl
   order. The ancestors of the modern day dolphins entered the water
   roughly fifty million years ago.
   Hind Limb Buds on Dolphins An embryo of a Spotted Dolphin in the fifth
   week of development. The hind limbs are present as small bumps (hind
   limb buds) near the base of the tail. The pin is approximately 1 inch
   (~2,5 cm) long.
   Hind Limb Buds on Dolphins An embryo of a Spotted Dolphin in the fifth
   week of development. The hind limbs are present as small bumps (hind
   limb buds) near the base of the tail. The pin is approximately 1 inch
   (~2,5 cm) long.
   Bottlenose Dolphin with vestigial hind flippers, captured 2006 in
   Japan.
   Bottlenose Dolphin with vestigial hind flippers, captured 2006 in
   Japan.

   Modern dolphin skeletons have two small, rod-shaped pelvic bones
   thought to be vestigial hind legs. In October 2006 an unusual
   Bottlenose Dolphin was captured in Japan; it had small fins on each
   side of its genital slit which scientists believe to be a more
   pronounced development of these vestigial hind legs.

Anatomy

   Dolphins have a streamlined fusiform body, adapted for fast swimming.
   The basic colouration patterns are shades of grey with a light
   underside and a distinct dark cape on the back. It is often combined
   with lines and patches of different hue and contrast.

   The head contains the melon, a round organ used for echolocation. In
   many species, the jaws are elongated, forming a distinct beak; for some
   species like the Bottlenose, there is a curved mouth which looks like a
   fixed smile. Teeth can be very numerous (up to two hundred and fifty)
   in several species. The dolphin brain is large and has a highly
   structured cortex, which often is referred to in discussions about
   their advanced intelligence.

   Unlike most mammals, dolphins do not have hair, but they are born with
   a few hairs around the tip of their rostrum which they lose after some
   time, in some cases even before they are born. The only exception to
   this is the Boto river dolphin, which does have some small hairs on the
   rostrum.

   Their reproductive organs are located on the underside of the body.
   Males have two slits, one concealing the penis and one further behind
   for the anus. The female has one genital slit, housing the vagina and
   the anus. A mammary slit is positioned on either side of the female's
   genital slit.

Senses

   Most dolphins have acute eyesight, both in and out of the water, and
   their sense of hearing is superior to that of humans. Though they have
   a small ear opening on each side of their head, it is believed that
   hearing underwater is also if not exclusively done with the lower jaw
   which conducts the sound vibrations to the middle ear via a fat-filled
   cavity in the lower jaw bone. Hearing is also used for echolocation,
   which seems to be an ability all dolphins have. Their teeth are
   arranged in a way that works as an array or antenna to receive the
   incoming sound and make it easier for them to pinpoint the exact
   location of an object. The dolphin's sense of touch is also
   well-developed. However, dolphins lack an olfactory nerve and lobes and
   thus are believed to have no sense of smell, but they can taste and do
   show preferences for certain kinds of fish. Since dolphins spend most
   of their time below the surface normally, just tasting the water could
   act in a manner analogous to a sense of smell.

   Though most dolphins do not have any hair, they do still have hair
   follicles and it is believed these might still perform some sensory
   function, though it is unclear what exactly this may be. The small
   hairs on the rostrum of the Boto river dolphin are believed to function
   as a tacticle sense however, possibly to compensate for the Boto's poor
   eyesight.

Behaviour

   Pacific White-Sided Dolphins breaching
   Pacific White-Sided Dolphins breaching

   Dolphins are often regarded as one of Earth's most intelligent animals,
   though it is hard to say just how intelligent dolphins are, as
   comparisons of species' relative intelligence are complicated by
   differences in sensory apparatus, response modes, and nature of
   cognition. Furthermore, the difficulty and expense of doing
   experimental work with large aquatics means that some tests which could
   meaningfully be done still have not been carried out, or have been
   carried out with inadequate sample size and methodology. Dolphin
   behaviour has been studied extensively by humans however, both in
   captivity and in the wild. See the cetacean intelligence article for
   more details.

Social behaviour

   Dolphins surfing at Snapper Rocks, Queensland, Australia.
   Dolphins surfing at Snapper Rocks, Queensland, Australia.

   Dolphins are social, living in pods (also called "schools") of up to a
   dozen individuals. In places with a high abundance of food, pods can
   join temporarily, forming an aggregation called a superpod; such
   groupings may exceed a thousand dolphins. The individuals communicate
   using a variety of clicks, whistles and other vocalizations. They also
   use ultrasonic sounds for echolocation. Membership in pods is not
   rigid; interchange is common. However, the cetaceans can establish
   strong bonds between each other. This leads to them staying with
   injured or ill individuals for support.

   In May 2005, researchers in Australia discovered a cultural aspect of
   dolphin behaviour: Some dolphins (Tursiops aduncus) teach their
   children to use tools. The dolphins break sponges off and cover their
   snouts with them thus protecting their snouts while foraging. This
   knowledge of how to use a tool is mostly transferred from mothers to
   daughters, unlike simian primates, where the knowledge is generally
   passed on to both sexes. The technology to use sponges as mouth
   protection is not genetically inherited but a taught behaviour.

   They are also willing to occasionally approach humans and playfully
   interact with them in the water. Dolphins have also been known to
   protect swimmers from sharks by swimming circles around them.

   Dolphins are known to engage in acts of aggression towards each other.
   The older a male dolphin is, the more likely his body is covered with
   scars ranging in depth from teeth marks made by other dolphins. It is
   suggested that male dolphins engage in such acts of aggression for the
   same reasons as humans: disputes between companions or even competition
   for other females. Acts of aggression can become so intense that
   targeted dolphins are known to go into exile, leaving their communities
   as a result of losing a fight with other dolphins.

   Male Bottlenose Dolphins have been known to engage in infanticide.
   Dolphins have also been known to kill porpoises for reasons which are
   not fully understood, as porpoises generally do not share the same fish
   diet as dolphins and are therefore not competitors for food supplies.

Reproduction

   Dolphin copulation happens belly to belly and though many species
   engage in lengthy foreplay, the actual act is usually only brief, but
   may be repeated several times with a few minutes in between. The
   gestation period varies per species.

   Dolphins are one of the few animals other than humans known to mate for
   reasons other than reproduction. Male Bottlenose Dolphins are known to
   engage in sexual acts with other dolphin species, which is not always
   consensual, though the Bottlenose may also be submissive in such
   encounters. Occasionally, dolphins will also show sexual behaviour
   towards humans.

Feeding

   Individual species may employ a number of methods of hunting, but even
   within a species various feeding methods may be employed, some being
   used by only a single dolphin population. Fish and squid are the main
   source of food for most dolphin species, but the False Killer Whale and
   the Killer Whale also feed on other marine mammals.

   One feeding method employed by many species is herding, where a pod
   will control a school of fish while individual members take turns
   plowing through the school, feeding. The tightly packed school of fish
   is commonly known as bait ball. Coralling is a method where fish are
   chased to shallow water where they are more easily captured. In South
   Carolina, the Atlantic Bottlenose Dolphin takes this one step further
   with what has become known as strand feeding, where the fish are driven
   onto mud banks and retrieved from there. In some places, Orcas will
   also come up to the beach to capture seals. Some species also whack
   fish with their fluke, stunning them and sometimes sending fish clear
   out of the water.

   Reports of cooperative human-dolphin fisheries date back to the ancient
   Roman author and natural philospher Pliny. A modern human-dolphin
   fishery still takes place in Laguna, Santa Catarina, Brazil.

Jumping and playing

   Dolphins often leap above the water surface, sometimes performing
   acrobatic figures (e.g. the spinner dolphin). Scientists are not always
   quite certain about the purpose of this behaviour and the reason for it
   may vary, it could be to locate schools of fish by looking at
   above-water signs like feeding birds, they could be communicating to
   other dolphins to join a hunt, attempting to dislodge parasites, or
   simply doing it for fun. Play is a very important part of dolphins'
   lives, and they can often be observed playing with seaweed or
   play-fighting with other dolphins. They even harass other locals, like
   seabirds and turtles. Dolphins also seem to enjoy riding waves and
   frequently 'surf' coastal swells and the bow waves of boats.

Human-dolphin relationships

Mythology

   Dolphins have long played a role in human culture. Dolphins are common
   in Greek mythology and there are many coins from the time which feature
   a man or boy riding on the back of a dolphin. The Ancient Greeks
   treated them with welcome; a ship spotting dolphins riding in their
   wake was considered a good omen for a smooth voyage. Dolphins also seem
   to have been important to the Minoans, judging by artistic evidence
   from the ruined palace at Knossos. In Hindu mythology, the Ganges River
   Dolphin is associated with Ganga, the deity of the Ganges river.

Therapy

   Dolphins are used in animal-assisted therapy, to help with various
   psychological and neurological problems such as autism, depression,
   Down syndrome and various development problems, and has shown to be
   beneficial for the participants.

Entertainment

   The famous Orca Keiko from the Free Willy movies being prepared for
   transport.
   The famous Orca Keiko from the Free Willy movies being prepared for
   transport.

   In more recent times, the 1963 Flipper movie and the subsequent popular
   Flipper television series, contributed to the popularity of dolphins in
   Western society. The series, created by Ivan Tors, portrayed a dolphin
   in a friendly relationship with two boys, Sandy and Bud; a kind of
   seagoing Lassie. Flipper, a Bottlenose Dolphin, understood English
   unusually well and was a marked hero. A second Flipper movie was made
   in 1996, which was based on the story of the original movie. A
   Bottlenose Dolphin also played a prominent role in the 1990s science
   fiction television series seaQuest DSV in which the animal, named
   Darwin, could communicate with English speakers using a vocoder, a
   fictional invention which translated the clicks and whistles to English
   and back.
   A young couple being entertained by a trained Bottlenose Dolphin in
   Puerto Plata, Dominican republic.
   A young couple being entertained by a trained Bottlenose Dolphin in
   Puerto Plata, Dominican republic.

   More well known from this time period is probably the movie Free Willy
   however, which made famous the Orca playing Willy, Keiko. The 1977
   horror movie Orca paints a less friendly picture of the animal. Here, a
   male Orca takes revenge on fishermen after the killing of his mate. In
   the 1973 movie The Day of the Dolphin trained dolphins are kidnapped
   and made to perform a naval military assassination using explosives.

   The renewed popularity of dolphins in the 1960s resulted in the
   appearance of many dolphinariums around the world, which have made
   dolphins accessible to the public. Though criticism and more strict
   animal welfare laws have forced many dolphinariums to close their
   doors, hundreds still exist around the world attracting large amount of
   visitors. In the United States, best known are the SeaWorld marine
   mammal parks, and their common Orca stage name Shamu, which they have
   trademarked, has become well known. Southwest Airlines, an American
   airline, has even painted three of their Boeing 737 aircraft in Shamu
   colours as an advertisement for the parks and have been flying with
   such a livery on various aircraft since 1988.

   Occasionally, dolphins make an appearance in computer games. Best known
   is the Ecco the Dolphin game series. The games are named after their
   main character, Ecco, a young Bottlenose Dolphin. The Ecco the Dolphin
   games hinge on the idea that cetaceans are sapient beings and have
   their own underwater society.

   A well known American National Football League (NFL) team is named the
   Miami Dolphins. Their logo depicts an aqua-coloured Bottlenose Dolphin
   wearing an American football helmet and jumping in front of a
   coral-coloured sunburst.

Military

   A number of militaries have employed dolphins for various purposes from
   finding mines to rescuing lost or trapped humans. Such military
   dolphins, however, drew scrutiny during the Vietnam War when rumors
   circulated that dolphins were being trained to kill Vietnamese skin
   divers. Best known today is the U.S. Navy Marine Mammal Program.

Literature

   Dolphins are also common in contemporary literature, especially science
   fiction novels. A military role for dolphins is found in William
   Gibson's short story Johnny Mnemonic, in which cyborg dolphins are used
   in war-time by the military to find submarines and, after the war, by a
   group of revolutionaries to decode encrypted information. Dolphins play
   a role as sentient patrollers of the sea enhanced with a deeper empathy
   toward humans in Anne McCaffrey's The Dragonriders of Pern series. More
   humorous is The Hitchhiker's Guide to the Galaxy, in which dolphins are
   the second most intelligent creatures on Earth (after mice, and
   followed by humans) and tried in vain to warn humans of the impending
   destruction of the planet. However, their behaviour was misinterpreted
   as playful acrobatics. Their story is told in So Long, and Thanks for
   All the Fish. Much more serious is their major role (along with
   chimpanzees) in David Brin's Uplift series. A talking Dolphin called
   "Howard" helps Hagbard Celine and his submarine crew fight the evil
   Illuminati in Robert Shea and Robert Anton Wilson's epic: Illuminatus
   Trilogy

   Dolphins also appear frequently in non-science fiction literature
   however. In the book The Music of dolphins by author Karen Hesse, a
   girl is raised by dolphins from the age of four until she is discovered
   by the coast guard. Fantasy author Ken Grimwood wrote dolphins into his
   1995 novel Into the Deep about a marine biologist struggling to crack
   the code of dolphin intelligence, including entire chapters written
   from the viewpoint of his dolphin characters. In this book, humans and
   dolphins are capable of communicating via telepathy.

Human threats to dolphins

   Dead Atlantic White-Sided Dolphins in Hvalba on the Faroe Islands,
   killed in a drive hunt.
   Dead Atlantic White-Sided Dolphins in Hvalba on the Faroe Islands,
   killed in a drive hunt.

   Some dolphin species face an uncertain future, especially some of the
   river dolphin species such as the Amazon River dolphin, and the Ganges
   and Yangtze River dolphin, all of which are critically or seriously
   endangered. A 2006 survey found no individuals of the Yangtze River
   dolphin, leading to the conclusion that the species is now functionally
   extinct.

   Contamination of environment - the oceans, seas, and rivers - is an
   issue of concern, especially pesticides, heavy metals, plastics, and
   other industrial and agricultural pollutants which do not disintegrate
   rapidly in the environment are reducing dolphin populations, and
   resulting in dolphins building up unusually high levels of
   contaminants. Injuries or deaths due to collisions with boats,
   especially their propellers, are also common.

   Various fishing methods, most notably purse seine fishing for tuna and
   the use of drift and gill nets, results in a large amounts of dolphins
   being killed inadvertently. Accidental by-catch in trout nets is common
   and poses a risk for mainly local dolphin populations. In some parts of
   the world, such as some areas in Japan and the Faroe Islands, dolphins
   are traditionally considered as food, and killed in harpoon or drive
   hunts.

2007: Year of the Dolphin

   The year 2007 has been declared as (International) Year of the Dolphin
   by the United Nations and United Nations Environment Programme ( UNEP).
   The idea was launched by the UN's Convention on Migratory Species and
   the Whale and Dolphin Conservation Society (WDCS).
   Retrieved from " http://en.wikipedia.org/wiki/Dolphin"
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