- This article is about the dolphin mammal. For other uses of the term, please see dolphin (disambiguation).
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 1.2 metres and 40 kg (Heaviside's Dolphin), up to 9.5 metres and 10 tonnes (the Orca). Most species weigh between about 50 and about 200 kg. They are found worldwide, mostly in the shallower seas of the continental shelves, and all are carnivores, mostly taking 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.
- Suborder Odontoceti, toothed whales
- Family Delphinidae, oceanic Dolphins
- Genus Delphinus
- Long-Beaked Common Dolphin, Delphinus capensis
- Short-Beaked Common Dolphin, Delphinus delphis
- Genus Tursiops
- Genus Lissodelphis
- Genus Sotalia
- Genus Sousa
- Genus Stenella
- Genus Steno
- Rough-Toothed Dolphin, Steno bredanensis
- Genus Cephalorynchus
- Genus Grampus
- Genus Lagenodelphis
- 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
- Genus Peponocephalia
- Melon-headed Whale, Peponocephalia electra
- Genus Orcinus
- Genus Feresa
- Genus Pseudorca
- Genus Globicephala
- Family Platanistoidae, River Dolphins
- Genus Inia
- Boto (Amazon River Dolphin,)Inia geoffrensis
- Genus Lipotes
- Genus Platanista
- Genus Pontoporia
Six animals in the family Delphinidae are commonly called "whales" but are strictly speaking dolphins. They are sometimes called "blackfish":
Evolution of dolphins
Dolphins, along with whales and porpoises, are descendants of land-living mammals, most likely of the Artiodactyl order. 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 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 pattern 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.
Dolphins are widely believed to be amongst the most intelligent of all animals, 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 behaviour 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 has been a report of dolphins protecting swimmers against a shark by swimming circles around the swimmers.
Dolphins are social animals, living in so called schools of up to a dozen animals. In places with high abundance of food, schools can join temporarily forming aggregations of over 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.
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 attracton at places such as 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.
Dolphins do not have acute eyesight, but have good hearing and a keen sense of smell.
Compare also: whale behaviour
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))
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 behaviour was misinterpreted as playful acrobatics. Their story is told in So Long, and Thanks for All the Fish.
Ecco The Dolphin stars in a series of games for the Sega Genesis and Sega Dreamcast.
See also: dolphin (mythology)
- 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/)
- 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/dolphin_sheet.htm)
- pictures of dolphins (http://www.hickerphoto.com/categories.php?cat_id=45)