Dolphin

?
Dolphin
Pacific White-sided Dolphins
Pacific White-sided Dolphins
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Family: Delphinidae
Genera
See article below.

Dolphins are 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:

  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 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 m (4 ft) and 40 kg (88 lb) ( Maui's Dolphin), up to 9.5 m (30 ft) and 10 tonnes (the Orca). 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 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.

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
      • 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 (the Chinese variant), Sousa chinensis chinensis
        • Atlantic Humpbacked Dolphin, Sousa teuszii
      • 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
        • Australian Snubfin Dolphin, Orcaella heinsohni
        • 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
    • Family Platanistoidea, 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

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

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 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.

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 behaviour

Dolphins in balance.
Dolphins in balance.

Dolphins are widely believed to be amongst the most intelligent of all animals. A typical statement would be that dolphins are roughly as intelligent as a two-year-old human. However, experts in comparative psychology or animal cognition would be reluctant to make any such estimate, as quantitative comparisons of intelligence between species are notoriously difficult to make in principle. 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 a large marine animal mean that even such tests as can meaningfully be done have still not been done, or have been carried out with inadequate sample size 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). Scientists aren't quite certain about the purpose of this behaviour, 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, or attempting to dislodge parasites. Perhaps they just do 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. 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 are many stories of dolphins protecting shipwrecked sailors against sharks by swimming circles around the swimmers.

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.

Dolphin leaping in the air.
Dolphin leaping in the air.

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, 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. 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.

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.

In captivity, many dolphins seem to have committed suicide. They either do so by repeatedly slamming their head against the pool walls or other solid objects or simply by not coming up for air anymore. Probably one of the best known cases of dolphin suicide is that of a dolphin named Cathy, one of the bottlenose dolphins that performed in the television series Flipper. She most likely died of self induced asphyxiation in the presence of her trainer Richard O'Barry. [1]

Compare also: whale behaviour

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 hearing underwater is also if not exclusively done with the lower jaw which conducts the 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, they seem to lack a well-developed sense of smell, but they most likely 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 as 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 large 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. [2]

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. 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.
  • 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 behaviour was misinterpreted as playful acrobatics. Their story is told in So Long, and Thanks for All the Fish. See Races from 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.
  • 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, the SOL gets blasted by a ship that turns out to be piloted by dolphins. Mike and the 'Bots then quickly apoligize.
  • 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 reconaissance 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.