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Dolphin

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Dolphin
File:Duskydolphin17.jpg
Pacific White-sided Dolphins
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Cetacea
Suborder:
Odontoceti
Family:
Delphinidae

Gray, 1821
Genera

See article below.

For other uses, see Dolphin (disambiguation).

Dolphins are aquatic mammals related to whales and porpoises, famous for their intelligence, apparent compassion, and joy. The name is from Ancient Greek Template:Polytonic delphis meaning "with a womb", viz. "a 'fish' with a womb". A group of dolphins can be called a "school" or a "pod".

The word is used in a few different ways. It can mean:

  1. Any member of the family Delphinidae (oceanic dolphins),
  2. Any member of the families Delphinidae and Platanistoidea (oceanic and river dolphins),
  3. Any member of the suborder Odontoceti (toothed whales; these include the above families and some others),
  4. 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 related species belong to the Delphinidae family and therefore qualify as dolphins, even though they are called whales in common language. There are almost 40 species of dolphin in 17 genera. They vary in size from 1.2 m (4 ft) and 40 kg (88 lb) (Maui's Dolphin), up to 9.5 m (30 ft) and 10 tonnes (the Orca). However, the average length for most North American species is 13.89 feet in length. Most species weigh about 50 to 200 kg (110 to 440 lb). 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 10 million years ago, during the Miocene.

Taxonomy

Six animals in the family Delphinidae are commonly called "whales" but are strictly speaking dolphins. They are sometimes called "blackfish".

Hybrid dolphins

In 1933, three strange 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. In the wild, Spinner Dolphins have sometimes hybridised with Spotted Dolphins and Bottlenose Dolphins. In the wild, bands of males of one dolphin species have been observed to mate with lone female Spinners. Blue Whales, Fin Whales and Humpback Whales all hybridize in the wild. Dall's Porpoises and Harbour Porpoises have hybridized in the wild. There has also been a reported hybrid between a beluga and a narwhal. See also wolphin.

Evolution and anatomy of dolphins

Dolphins, along with whales and porpoises, are thought to be descendants of land-living mammals, most likely of the Artiodactyl order. Modern dolphin skeletons have two small rod shaped pelvic bones thought to be left-over hind legs. They entered the water roughly 50 million years ago. See evolution of cetaceans for the details.

Dolphins have a fusiform body, adapted for fast swimming. 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 that looks like a fixed smile. Teeth can be very numerous (up to 250) in several species. The dolphin brain is large and has a highly structured cortex, which often is referred to in discussions about their high intelligence. A recent theory however suggests that this may not be the case and that the large brain is only an adaptation to living in cold water, however this theory contradicts current knowledge.[1] Their teeth are arranged in a way that works as an array or antenna focusing the incoming sound, making it easier for them to pinpoint the exact location of an object. The basic coloration patterns are shades of gray 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. See individual species articles for details.

Dolphin behavior

See also: Whale behavior
Bottlenose dolphin in the bow wave of a boat

Dolphins are often regarded as one of the most intelligent animal species, though it is hard to say just how intelligent dolphins are as straightforward 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 marine animals means that some tests that could meaningfully be done still have not been carried out, or have been carried out with inadequate sample size and methodology. See the cetacean intelligence article for more details.

Dolphins often leap above the water surface, sometimes performing acrobatic figures (e.g. the spinner dolphin). Scientists are not quite certain about the purpose of this behavior, but it may be to locate schools of fish by looking at above water signs, like feeding birds. They could also 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 playfighting with other dolphins. They have even been seen harassing other creatures, like seabirds and turtles. Dolphins also seem to enjoy riding waves and are frequently seen 'surfing' coastal swells and the bow waves of boats.

They are also famous for their willingness to occasionally approach humans and playfully interact with them in the water. In return, some cultures such as the Ancient Greeks treated them with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. There are many stories of dolphins protecting shipwrecked sailors against sharks by swimming circles around the swimmers.

Dolphins surfing at Snapper Rocks, Queensland, Australia.

Dolphins are social animals, living in pods (also called "schools") of up to a dozen animals. In places with a high abundance of food, schools can join temporarily, forming an aggregation called a superpod; such groupings may exceed 1000 dolphins. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation. Membership in schools is not rigid; interchange is common. However, the animals can establish strong bonds between each other. This leads to them staying with injured or ill fellows for support.

A young couple being entertained by trained Bottlenose Dolphins in Puerto Plata, Dominican republic.

Because of their high capacity for learning, dolphins have been employed by humans for any number of purposes. Dolphins trained to perform in front of an audience have become a favorite attraction in dolphinaria, for example SeaWorld. Such places may sometimes also provide an opportunity for humans to interact very closely with dolphins. Dolphin-human interaction is also employed in a curative sense at places where dolphins work with autistic or otherwise disabled children. The military has employed dolphins for various purposes from finding mines to rescuing lost or trapped persons. Such military dolphins, however, drew scrutiny during the Vietnam War when rumors circulated that dolphins were being trained to kill Vietnamese skin divers. Reports of cooperative human-dolphin fisheries date back to Pliny. A modern human-dolphin fishery was reported in Laguna, Santa Catarina, Brazil in 1990.

In May 2005, researchers in Australia discovered a cultural aspect of dolphin behaviour: Some dolphins (Tursiops aduncus) teach their offspring to use tools. The animals break off sponges and put them onto their mouths thus protecting the delicate body part during their hunt for fish on the seabed. This knowledge of how to use a tool is mostly transferred from mothers to daughters in dolphins, unlike simian primates, where the knowledge is generally passed onto all the offsprings, irrespective of sex. The technology to use sponges as mouth protection is not genetically inherited but a taught cultural behaviour.

Dolphins are one of the few animals other than humans known to mate for reasons other than procreation.[2] Sex does not appear to be consensual in all cases however, with male Bottlenose Dolphins even being known to molest females of other dolphin species.

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. The dolphin's sense of touch is also well-developed. However, dolphins lack an olfactory nerve and thus 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 in the wild, just tasting the water could act in a manner analogous to a sense of smell.

Feeding

Dolphins are predators, chasing their prey at high speed. The dentition is adapted to the animals they hunt: Species with long beaks and many teeth forage on fish, whereas short beaks and lesser tooth count are linked to catching squid. Some dolphins may take crustaceans. Usually, the prey is swallowed whole. The larger species, especially the orca, are capable of eating marine mammals, even small whales. There are no known reports of cannibalism amongst dolphins.

Individual species may employ a number of methods of hunting:

  • Herding - where a superpod will control a school of fish while individual members take turns plowing through the herd, feeding.
  • Corralling - where fish are chased to shallow water where they are more easily captured.
  • Fish Wacking - where the dolphin uses its fluke to strike the fish, stunning it and sometimes sending it clear out of the water.
  • Stunning - using the echolocation melon, very loud clicks are directed at prey, stunning them.
  • Foraging - A recent study reported that wild bottlenose dolphins (Tursiops) in Western Australia use sponges to forage in the sea bed for food.[3]
  • Mudding - Coastal bottlenose dolphins in South Carolina have been observed to drive fish onto mud banks and retrieve them from there.
  • The popular television show Flipper, created by Ivan Tors, portrayed a dolphin in a friendly relationship with two boys, Sandy and Bud; a kind of seagoing Lassie, Flipper understood English unusually well and was a marked hero: "Go tell Dad we're in trouble, Flipper! Hurry!" The show's theme song contains the lyric no one you see / is smarter than he. The television show was based on a 1963 film, and remade as a feature film in 1996 starring Elijah Wood and Paul Hogan (actor), as well as a television series running from 1995-2000 starring Jessica Alba.[4]
  • In The Hitchhiker's Guide to the Galaxy, dolphins are the second most intelligent creatures on Earth (after mice) and tried in vain to warn humans of the impending destruction of the planet. However, their behavior was misinterpreted as playful acrobatics. Their story is told in So Long, and Thanks for All the Fish. See Races and Species in The Hitchhiker's Guide to the Galaxy
  • After study at the Dolphins Plus research center in Key Largo, Florida, fantasy author Ken Grimwood wrote dolphins into his 1995 novel Into the Deep, including entire chapters written from the viewpoint of his dolphin characters.
  • A science fiction trilogy, The Dolphins' View, is ghost written by Mookeeo, the main dolphin character. The story presents the fun loving nature of dolphins while they are also on a quest to save their world.
  • Ecco the Dolphin stars in a series of games for the Sega Genesis/Mega Drive, Game Gear, Sega Dreamcast and PlayStation 2.
  • A book called The Music of Dolphins was written by Karen Hesse, about a girl who had lived with dolphins since the age of four.
  • An American National Football League (NFL) team is named the Miami Dolphins. Their logo depicts an aqua-colored bottlenose dolphin wearing an American football helmet and jumping in front of a coral-colored sunburst.
  • In the Mystery Science Theater 3000 episode "Devil Fish", Mike and the 'Bots mock dolphins. While doing so their craft, the Satellite of Love, gets blasted by a ship that turns out to be piloted by dolphins. Mike and the 'Bots then quickly apologize.
  • In seaQuest, Darwin the dolphin could communicate with English speakers using a vocoder, an invention that translated the clicks and whistles to English and back.
  • In The Life Aquatic with Steve Zissou, marine researcher Zissou (played by Bill Murray) has trained reconnaissance dolphins which apparently are temperamental and rarely follow their instructions. In one scene, the dolphins' misbehavior elicits the following quote from Zissou: "Son of a bitch, I'm sick of these dolphins."
  • In the book Startide Rising by author David Brin, the spaceship Streaker is manned by neo-dolphins (dolphins genetically engineered to match human intelligence). One of the mates of the ship is named Akeakamai, in honor of the real-life dolphin from Louis Herman's animal language research.
  • In the William Gibson short story Johnny Mnemonic and the film by the same name (starring Keanu Reeves), cyborg dolphins were used in war-time by the military to find submarines and, after the war, by a group of revolutionaries to decode encrypted information.
  • In the South Park episode "Weight Gain 4000," Eric Cartman believes that dolphins live in igloos.
  • In a Halloween episode of The Simpsons, dolphins reveal the ability to speak, walk on land, and their taste for humans.
  • In The Ballad of Halo Jones, Dolphins are a respected species that are the best at piloting spacecraft, and are very peaceful and anti-war.
  • In the Pern novels by Anne McCaffrey, the human colonists of Pern brought genetically-engineered dolphin volunteers as additional colonists. Capable of speech, these enhanced dolphins thrived in the seas of Pern and were instrumental in helping the colonists to sanctuary during the first years of Threadfall.

See also

Template:Cetaceaportal

References

  1. ^ An examination of cetacean brain structure with a novel hypothesis correlating thermogenesis to the evolution of a big brain, article by Paul Manger, 2006
  2. ^ BIRTH CONTROL, BISEXUALITY, DEATH BY CHOICE ...The dolphins have it all over us - article by Bob Hunter, eye weekly
  3. ^ http://www.pnas.org/cgi/content/abstract/0500232102v1
  4. ^ http://www.imdb.com/title/tt0111964
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