Dolphin
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Dolphins are certain aquatic mammals related to whales and porpoises. The name is from Ancient Greek δελφίς delphis meaning "with a womb", viz. "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 Platanistoidae (oceanic and river dolphins),
- any member of the suborder Odontoceti (toothed whales; these include the above families and some others),
- laypeople often use the term synonymously with 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 our 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 4 ft (1.2 m) and 88 lb (40 kg) (Maui's Dolphin), up to 31 ft (9.5 m) and 10 tonnes (the Orca). Most species weigh about 110 to 440 lb (50 to 200 kg). They are found worldwide, mostly in the shallower seas of the continental shelves, and all 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.
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Taxonomy
- Suborder Odontoceti, toothed whales
- Family Delphinidae, oceanic Dolphins
- Genus Delphinus
- Long-Beaked Common Dolphin, Delphinus capensis
- Short-Beaked Common Dolphin, Delphinus delphis
- Genus Tursiops
- Bottlenose Dolphin, Tursiops truncatus
- Genus Lissodelphis
- Northern Rightwhale Dolphin, Lissodelphis borealis
- Southern Rightwhale Dolphin, Lissiodelphis peronii
- Genus Sotalia
- Tucuxi, Sotalia fluviatilis
- Genus Sousa
- Indo-Pacific Hump-backed Dolphin Sousa chinensis
- Chinese White Dolphin is the Chinese variant
- Atlantic Humpbacked Dolphin, Sousa teuszii
- Indo-Pacific Hump-backed Dolphin Sousa chinensis
- Genus Stenella
- Atlantic Spotted Dolphin, Stenella frontalis
- Clymene Dolphin, Stenella clymene
- Pantropical Spotted Dolphin, Stenella attenuata
- Spinner Dolphin, Stenella longirostris
- Striped Dolphin, Stenella coeruleoalba
- Genus Steno
- Rough-Toothed Dolphin, Steno bredanensis
- Genus Cephalorynchus
- Chilean Dolphin, Cephalorhynchus eutropia
- Commerson's Dolphin, Cephalorhynchus commersonii
- Heaviside's Dolphin, Cephalorhynchus heavisidii
- Hector's Dolphin, Cephalorhynchus hectori
- Genus Grampus
- Risso's Dolphin, Grampus griseus
- Genus Lagenodelphis
- Fraser's Dolphin, Lagenodelphis hosei
- 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
- Genus Orcaella
- Irrawaddy Dolphin, Orcaella brevirostris
- Genus Peponocephalia
- Melon-headed Whale, Peponocephalia electra
- Genus Orcinus
- Killer Whale, Orcinus orca
- Genus Feresa
- Pygmy Killer Whale, Feresa attenuata
- Genus Pseudorca
- False Killer Whale, Pseudorca crassidens
- Genus Globicephala
- Long-finned Pilot Whale, Globicephala melas
- Short-finned Pilot Whale, Globicephala macrorhynchus
- Genus Delphinus
- Family Platanistoidae, River Dolphins
- Genus Inia
- Boto (Amazon River Dolphin,)Inia geoffrensis
- Genus Lipotes
- Chinese River Dolphin (Baiji) Lipotes vexillife
- Genus Platanista
- Ganges River Dolphin Platanista gangetica
- Indus River Dolphin Platanista minor
- Genus Pontoporia
- La Plata Dolphin (Franciscana) Pontoporia blainvillei
- Genus Inia
- Family Delphinidae, oceanic Dolphins
Six animals in the family Delphinidae are commonly called "whales" but are strictly speaking dolphins. They are sometimes called "blackfish":
- Melon-headed Whale, Peponocephalia electra
- Killer Whale, Orcinus orca
- Pygmy Killer Whale, Feresa attenuata
- False Killer Whale, Psudoorca crassidens
- Long-finned Pilot Whale, Globicephala melas
- Short-finned Pilot Whale, Globicephala macrorhynchus
Evolution of dolphins
Dolphins, along with whales and porpoises, are 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.
Dolphin anatomy
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.
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
Dolphins are widely believed to be amongst the most intelligent of all animals, about as smart as a two-year-old, give or take, although the difficulties and expense of doing experimental work with a large marine animal, with a very different sensory apparatus from our own, mean that many of the tests required to confirm this belief have not yet been done, or have been carried out with inadequate sample sizes and methodology. See the Dolphin intelligence article for more details.
Dolphins often leap above the water surface, sometimes performing acrobatic figures (e.g. the spinner dolphin). This and other behavior is interpreted as playing. They are capable of diving up to 260 m deep and 15 min long, but rarely stay underwater longer than few minutes. Frequently dolphins will accompany boats, riding the bow waves.
They are also famous for their willingness to occasionally approach humans and playfully interact with them in the water. In return, in some cultures like in Ancient Greece they were treated with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. There have been reports of dolphins protecting swimmers against sharks by swimming circles around the swimmers.
Dolphins are social animals, living in pods (aka schools) of up to a dozen animals. In places with high abundance of food, schools can join temporarily forming aggregations of over 1000 dolphins called a superpod. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation.
Airborne_dolphin.jpg
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.
Because of their high capacity for learning, humans have employed dolphins for any number of purposes. Dolphins trained to perform in front of an audience have become a favorite attraction in dolphinaria, for example SeaWorld. Dolphin/Human interaction is also employed in a curative sense at places where dolphins work with autistic or otherwise disabled children. The military too 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.
In May 2005, researchers in Australia discovered a cultural aspect of dolphin behaviour: Some dolphins (Tursiops aduncus) teach their offspring to use a tool. 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. Other than with primate simians, the knowledge to use a tool is mostly handed over only from mothers to daughters. The technology to use sponges as mouth protection is not genetically inherited but a taught cultural behaviour.
Dolphins do not have acute eyesight nor do they appear to have a good sense of smell, although their sense of hearing is far above our own.
Compare also: whale behavior
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 bigger species, especially the orca, are capable of eating marine mammals, even large whales. There are no known reports of cannibalism amongst dolphins. (See external link: Common Dolphin Prey Species in the Eastern Ionian Sea (http://www.accobams.org/download/articles/population/Agazzi_etal_2004.pdf))
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 sp.) in Western Australia use sponges to forage in the sea bed for food.[1] (http://www.pnas.org/cgi/content/abstract/0500232102v1)
Dolphin lore
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 sea going 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.
In The Hitchhiker's Guide to the Galaxy, dolphins are very intelligent creatures who tried in vain to warn humans of the impending destruction of Earth. However, their behavior was misinterpreted as playful acrobatics. Their story is told in So Long, and Thanks for All the Fish. 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.
Ecco The Dolphin stars in a series of games for the Sega Genesis, and Sega Dreamcast.
See also
Related articles
- John Lilly – Dolphin intelligence researcher
- Dolphin brain – Article on dolphin intelligence
External links
- Dolphins help lifeguards from sharks (http://news.bbc.co.uk/2/hi/asia-pacific/4034383.stm)
- Cetacea.org site (http://www.cetacea.org/)
- Facts and Information on Dolphins (http://www.robins-island.org/)
- Dolphin Pictures (http://www.hickerphoto.com/dolphin-pictures-cat.htm)
- Tursiops.org: Current Dolphin-related news (http://www.tursiops.org/)
- Wild Dolphin Foundation; Hawaiian Spinner Dolphin pictures, videos, information and conservation (http://www.wilddolphin.org/dolphinpictures.htm)
- PBS NOVA: Dolphins: Close Encounters (http://www.pbs.org/wnet/nature/dolphins/index.html)
- Common dolphin prey species in the eastern Ionian Sea (http://www.accobams.org/download/articles/population/Agazzi_etal_2004.pdf)
- facts about dolphins (http://www.whale-images.com/facts_about_dolphins.htm)