Oceanic dolphins orDelphinidae are a widely distributed family ofdolphins that live in thesea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as theGlobicephalinae (round-headed whales, which include thefalse killer whale andpilot whale). Delphinidae is a family within the superfamilyDelphinoidea, which also includes theporpoises (Phocoenidae) and theMonodontidae (beluga whale andnarwhal).River dolphins are relatives of the Delphinoidea.
Oceanic dolphins range in size from the 1.7-metre-long (5 ft 7 in) and 50-kilogram (110-pound)Maui's dolphin to the 9.4-metre (31 ft) and 10-metric-ton (11-short-ton)orca, the largest known dolphin. Several species exhibitsexual dimorphism; the males are larger than females. They have streamlined muscular bodies and two limbs that are modified into flippers. Though not quite as flexible asseals, some dolphins can travel at speeds 29 km/h (18 mph) for short distances.[1] Most delphinids primarily eat fish, along with a smaller number of squid and small crustaceans, but some species specialise in eating squid, or, in the case of the orca, also eat marine mammals and birds. All, however, are purelycarnivorous. They typically have between 100 and 200 teeth, although a few species have considerably fewer. Delphinids travel in large pods, which may number a thousand individuals in some species. Each pod forages over a range of tens to hundreds of square kilometres. Some pods have a loose social structure, with individuals frequently joining or leaving, but others seem to be more permanent, perhaps dominated by a male and aharem of females.[2] Individuals communicate by sound, producing low-frequency whistles, and also produce high-frequency broadband clicks of 80–220 kHz, which are primarily used forecholocation.Gestation lasts from 10 to 18 months, and results in the birth of a single calf. Some species are well adapted for diving to great depths. They have a layer of fat, orblubber, under the skin to keep warm in the cold water.
Although oceanic dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like theright whale dolphin, prefer colder climates. Some have a global distribution, like the orca. Oceanic dolphins feed largely on fish and squid, but a few, like the orca, feed on large mammals, like seals. Male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer, and females bear all the responsibility for raising them. Mothers of some species fast and nurse their young for relatively long times. Dolphins produce a variety of vocalizations, usually in the form of clicks and whistles.
Oceanic dolphins are sometimes hunted in places such as Japan, in an activity known asdolphin drive hunting. Besides drive hunting, they also face threats frombycatch, habitat loss, andmarine pollution. Dolphins have been depicted in various cultures worldwide. They occasionally feature in literature and film, as in the Warner Bros filmFree Willy. Dolphins are sometimes kept in captivity and trained to perform in shows. The most common species of dolphin in captivity is thebottlenose dolphin, and less than 50 orca were found inoceanariums in 2012.
Delphinids, especially bottlenose dolphins, are able tohybridize with a wide variety of other delphinid species;wholphins are just one of many possible hybrids.[3]
Recentmolecular analyses indicate that several delphinidgenera (especiallyStenella) are notmonophyletic as currently recognized.[5] Thus, significant taxonomic revisions within the family are likely.[6] In 2025 there was significant revision of the genusLagenorhynchus.[7]
A classification of the family Delphinidae from Perrin (1989) reflecting a traditional view of species interrelationships.
Revised classification of the family Delphinidae based on molecular systematic analysis; adapted from LeDuc et al. (1999) and McGowen et al. (2019).[8][9][10][11]
Species recognized by Society for Marine Mammalogy's taxonomic Committee (2025)[12][7]
The Delphinidae are the most diverse of the cetacean families, with numerous variations between species. They range in size from 1.2 m (3 ft 11 in) and 40 kg (88 lb) (Haviside's dolphin), to 9 m (30 ft) and 10 tonnes (orca). Most species weigh between 50 and 200 kg (110 and 440 lb). They typically have curved dorsal fins, clear 'beaks' at the front of their heads, and foreheadmelons, although exceptions to all of these rules are found. They have a wide range of colors and patterns.[2]
Oceanic dolphins have a torpedo-shaped, muscular body with an inflexible neck, limbs modified into flippers, nonexistent external ear flaps, a large tail fin, and a bulbous head. A dolphin skull has small eye orbits, a long snout, but not as long as itsriver dolphin counterpart, and eyes placed on the sides of its head. Several species exhibit sexual dimorphism, with the males being larger than the females.[14][15]
Breathing involves expelling stale air from theblowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs; a spout only occurs when the warm air from the lungs meets the cold external air, so it may only form in colder climates.[14][16][17]
All oceanic dolphins have a thick layer ofblubber, the thickness of which depends on how far the species lives from the equator. This blubber also helps keep the animal warm providing insulation from the harsh climate or cold depths. It can also aid in protection to some extent as predators would have a hard time getting through a thick layer of fat. Calves are born with only a thin layer of blubber, but some species compensate for this withlanugos.[14][18]
Oceanic dolphins have two flippers on the underside toward the head, adorsal fin, and a tail fin. These flippers contain four digits. Although oceanic dolphins do not possess fully developed hind limbs, some possess discrete rudimentary appendages, which may contain feet and digits. Oceanic dolphins are fast swimmers in comparison to seals who typically cruise at 11–27 km/h (7–17 mph); the orca, in comparison, can travel at speeds of up to 55.5 km/h (34.5 mph). The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, which means they are unable to turn their heads. Oceanic dolphins swim by moving their tail fin and rear body vertically, while their flippers are mainly used for steering. Some specieslog out of the water, which may allow them to travel faster. Their skeletal anatomy allows them to be fast swimmers. All species have adorsal fin to prevent themselves from involuntarily spinning in the water.[14][18]
The oceanic dolphin ear is specifically adapted to themarine environment. In humans, themiddle ear works as an impedance equalizer between the outside air's lowimpedance and thecochlear fluid's high impedance. In dolphins, and other marine mammals, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, dolphins receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The dolphin ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.[19] Dolphins send out high frequency clicks from an organ known as amelon. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. This allows dolphins to producebiosonar for orientation.[14][20][21][22][23] Though most dolphins do not have hair, they do havehair follicles that may perform some sensory function.[24] Beyond locating an object, echolocation also provides the animal with an idea on an object's shape and size, though how exactly this works is not yet understood.[25]
The eye of oceanic dolphins is relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes of a dolphin are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When dolphins surface, their lens and cornea correct the nearsightedness that results from the refraction of light; they contain bothrod andcone cells, meaning they can see in both dim and bright light. Dolphins do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for color vision than most mammals.[26] Most dolphins have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and atapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. They also have glands on the eyelids andouter corneal layer that act as protection for the cornea.[20]
Theolfactory lobes are absent in oceanic dolphins, suggesting that they have no sense of smell.[20]
Oceanic dolphins are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. However, some have preferences between different kinds of fish, indicating some sort of attachment to taste.[20]
Most delphinids primarily eat fish, along with a smaller number of squid and small crustaceans, but some species specialize in eating squid, or, in the case of the orca, also eat marine mammals and birds. All, however, are purelycarnivorous. They typically have between 100 and 200 teeth, although a few species have considerably fewer. Various methods of feeding exist among and within oceanic species, some apparently exclusive to a single population. Fish and squid are the main food, but thefalse killer whale and the orca also feed on other marine mammals. Orca on occasion also huntwhales larger than themselves.[27]
One common feeding method is herding, where a pod squeezes a school of fish into abait ball. Individual members then take turns plowing through the ball, feeding on the stunned fish. Corralling is a method where dolphins chase fish into shallow water to catch them more easily. Orca and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it, a behavior known as beach or strand feeding. Some species also whack fish with their flukes, stunning them and sometimes knocking them out of the water.[28]
Oceanic dolphins are capable of making a broad range of sounds using nasal airsacs located just below the blowhole. Roughly three categories of sounds can be identified:frequency modulated whistles, burst-pulsed sounds, and clicks. Dolphins communicate with whistle-like sounds produced by vibrating connective tissue, similar to the way human vocal cords function,[29] and through burst-pulsed sounds, though the nature and extent of that ability is not known. The clicks are directional and are for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Dolphin echolocation clicks are amongst theloudest sounds made by marine animals.[30]
Bottlenose dolphins have been found to have signature whistles. These whistles are used in order for dolphins to communicate with one another by identifying an individual. It can be seen as the dolphin equivalent of aname for humans.[31] These signature whistles are developed during a dolphin's first year; it continues to maintain the same sound throughout its lifetime.[32] In order to obtain each individual whistle sound, dolphins undergo vocal production learning. This consists of an experience with other dolphins that modifies the signal structure of an existing whistle sound. An auditory experience influences the whistle development of each dolphin. Dolphins are able to communicate to one another by addressing another dolphin through mimicking their whistle. The signature whistle of a male bottlenose dolphin tends to be similar to that of his mother, while the signature whistle of a female bottlenose dolphin tends to be more distinguishable.[33] Bottlenose dolphins have a strong memory when it comes to these signature whistles, as they are able to relate to a signature whistle of an individual they have not encountered for over twenty years.[34] Research done on signature whistle usage by other dolphin species is relatively limited. The research on other species done so far has yielded varied outcomes and inconclusive results.[35][36][37][38]
Oceanic dolphins frequently leap above the water surface, this being done for various reasons. When travelling, jumping can save the dolphin energy as there is less friction while in the air.[39] This type of travel is known as porpoising.[39] Other reasons include orientation, social displays, fighting,non-verbal communication, entertainment and attempting to dislodgeparasites.[40][41]
Dolphins show various types ofplayful behavior, often including objects, self-madebubble rings, other dolphins, or other animals.[42][43] When playing with objects or small animals, common behavior includes carrying the object or animal along using various parts of the body, passing it along to other members of the group or taking it from another member, or throwing it out of the water.[42] Dolphins have also been observed harassing animals in other ways, for example by dragging birds underwater without showing any intent to eat them.[42] Playful behaviour that involves another animal species with active participation of the other animal can also be observed, however. Playful human interaction with dolphins is one example, but playful interactions have been observed in the wild with a number of other species as well, includinghumpback whales anddogs.[44][45]
Oceanic dolphins are known to teach, learn, cooperate, scheme, and grieve.[46] The neocortex of many species is home to elongatedspindle neurons that, prior to 2007, were known only in hominids.[47] In humans, these cells are involved in social conduct, emotions, judgment, and theory of mind.[48] Cetacean spindle neurons are found in areas of the brain that are homologous to where they are found in humans, suggesting that they perform a similar function.[49]
Brain size was previously considered a major indicator of the intelligence of an animal. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks.Allometric analysis indicates that mammalian brain size scales at approximately the2/3 or3/4 exponent of the body mass.[50] Comparison of a particular animal's brain size with the expected brain size based on such allometric analysis provides anencephalization quotient that can be used as another indication of animal intelligence.Orca have the second largest brain mass of any animal on earth, next to thesperm whale.[51] Thebrain to body mass ratio in some is second only to humans.[52]
Self-awareness is seen, by some, to be a sign of highly developed, abstract thinking. Self-awareness, though not well-defined scientifically, is believed to be the precursor to more advanced processes likemeta-cognitive reasoning (thinking about thinking) that are typical of humans. Research in this field has suggested that cetaceans, among others, possess self-awareness.[53]The most widely used test for self-awareness in animals is themirror test in which a temporary dye is placed on an animal's body, and the animal is then presented with a mirror; they then see if the animal shows signs of self-recognition.[54]
In 1995, Marten and Psarakos used television to test dolphin self-awareness.[55] They showed dolphins real-time footage of themselves, recorded footage, and another dolphin. They concluded that their evidence suggested self-awareness rather than social behavior. While this particular study has not been repeated since then, dolphins have since passed the mirror test.[54]
In some parts of the world, such asTaiji, Japan and theFaroe Islands, dolphins are traditionally considered as food, and are killed inharpoon ordrive hunts.[56]Dolphin meat is consumed in a small number of countries worldwide, which includeJapan[57] andPeru (where it is referred to aschancho marino, or "sea pork").[58]
Dolphin meat is dense and such a dark shade of red as to appear black. Fat is located in a layer ofblubber between the meat and the skin. When dolphin meat is eaten in Japan, it is often cut into thin strips and eaten raw assashimi, garnished with onion and eitherhorseradish or gratedgarlic, much as withsashimi ofwhale orhorse meat (basashi). When cooked, dolphin meat is cut into bite-size cubes and then batter-fried or simmered in amiso sauce with vegetables. Cooked dolphin meat has a flavor very similar tobeef liver.[59] Dolphin meat is high in mercury, and may pose danger to a humans health when consumed.[60]
TheFaroe Islands population was exposed tomethylmercury largely from contaminated pilot whale meat, which contained very high levels of about 2 mg methylmercury/kg. However, the Faroe Islands populations also eat significant amounts of fish. The study of about 900 Faroese children showed that prenatal exposure to methylmercury resulted in neuropsychological deficits at 7 years of age
There have been human health concerns associated with the consumption of dolphin meat in Japan after tests showed that dolphin meat contained high levels ofmercury.[61] There are no known cases ofmercury poisoning as a result of consuming dolphin meat, though the government continues to monitor people in areas where dolphin meat consumption is high. The Japanese government recommends that children and pregnant women avoid eating dolphin meat on a regular basis.[62]
Similar concerns exist with the consumption of dolphin meat in theFaroe Islands, whereprenatal exposure tomethylmercury andPCBs primarily from the consumption of pilot whale meat has resulted inneuropsychological deficits amongst children.[61]
Legallyconsuming dolphin meat in the United States would be near impossible for most due to theMarine Mammal Protection Act, which forbids "...the act of hunting, killing, capture, and/or harassment of any marine mammal..." (Exceptions are made for certain groups of people, such asAlaska Natives.) Theoretically, one could only eat the meat of a dolphin which died of natural causes, which would likely be highly undesirable (and potentially dangerous).[citation needed]
Various fishing methods, likeseine fishing fortuna and the use ofdrift andgill nets, unintentionally kill many oceanic dolphins.[63] Accidental bycatch in gill nets is common and poses a risk for mainly local dolphin populations.[64][65]
Dolphin safe labels attempt to reassure consumers that fish and other marine products have been caught in a dolphin-friendly way. The earliest campaigns with "Dolphin safe" labels were initiated in the 1980s as a result of cooperation between marine activists and the major tuna companies, and involved decreasing incidental dolphin kills by up to 50% by changing the type of nets used to catch tuna. The dolphins are netted only while fishermen are in pursuit of smaller tuna. Albacore are not netted this way, making albacore the only truly dolphin-safe tuna.[66]
Loud underwater noises, such as those resulting fromnavalsonar use, live firing exercises, and certainoffshore construction projects such aswind farms, may be harmful to dolphins, increasing stress, damaging hearing, and causingdecompression sickness by forcing them to surface too quickly to escape the noise.[67][68]
Orca are well known for their performances in shows, but the number of orcas kept in captivity is very small, especially when compared to the number of bottlenose dolphins, with only 44captive orca being held in aquaria as of 2012.[69] The orca'sintelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquaria and aquatic theme parks. From 1976 to 1997, 55 whales were taken from the wild in Iceland, 19 in Japan and three in Argentina. These figures exclude animals that died during capture. Live captures fell dramatically in the 1990s, and by 1999, about 40% of the 48 animals on display in the world were captive-born.[18]
InGreek myths, they were seen invariably as helpers of humankind. Dolphins also seem to have been important to theMinoans, judging by artistic evidence from the ruined palace atKnossos. Dolphins are common inGreek mythology, and many coins fromancient Greece have been found which feature a man, a boy or a deity riding on the back of a dolphin.[70] TheAncient Greeks welcomed dolphins; spotting dolphins riding in a ship's wake was considered a good omen.[71] In both ancient and later art,Cupid is often shownriding a dolphin. A dolphin rescued the poetArion from drowning and carried him safe to land, atCape Matapan, a promontory forming the southernmost point of thePeloponnesus. There was a temple toPoseidon and a statue of Arion riding the dolphin.[72]
Dionysus was once captured byEtruscanpirates who mistook him for a wealthy prince they could ransom. After the ship set sail Dionysus invoked his divine powers, causing vines to overgrow the ship where the mast and sails had been. He turned the oars into serpents, so terrifying the sailors that they jumped overboard, but Dionysus took pity on them andtransformed them into dolphins so that they would spend their lives providing help for those in need. Dolphins were also the messengers ofPoseidon and sometimes did errands for him as well. Dolphins were sacred to bothAphrodite andApollo.[citation needed]
Dolphins are sometimes used as symbols, for instance in heraldry. When heraldry developed in theMiddle Ages, not much was known about the biology of the dolphin and it was often depicted as a sort of fish. Traditionally, the dolphins in heraldry still may take after this notion, sometimes showing the dolphin skin covered withfish scales.[citation needed]
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