Delphinidae is a family within the superfamily Delphinoidea, which also includes the porpoises (Phocoenidae) and the Monodontidae (beluga whale and narwhal).

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 a harem of females.

They typically have curved dorsal fins, clear 'beaks' at the front of their heads, and forehead melons, although exceptions to all of these rules are found.

[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.

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.

The dolphin ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.

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.

Dolphins do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for color vision than most mammals.

[25] Most dolphins have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area.

Fish and squid are the main food, but the false killer whale and the orca also feed on other marine mammals.

[27] Oceanic dolphins are capable of making a broad range of sounds using nasal airsacs located just below the blowhole.

[38] Other reasons include orientation, social displays, fighting, non-verbal communication, entertainment and attempting to dislodge parasites.

[41] Dolphins have also been observed harassing animals in other ways, for example by dragging birds underwater without showing any intent to eat them.

Allometric analysis indicates that mammalian brain size scales at approximately the ⅔ or ¾ exponent of the body mass.

[53] In some parts of the world, such as Taiji, Japan and the Faroe Islands, dolphins are traditionally considered as food, and are killed in harpoon or drive hunts.

[55] Dolphin meat is consumed in a small number of countries worldwide, which include Japan[56] and Peru (where it is referred to as chancho marino, or "sea pork").

When cooked, dolphin meat is cut into bite-size cubes and then batter-fried or simmered in a miso sauce with vegetables.

[59] The Faroe Islands population was exposed to methylmercury largely from contaminated pilot whale meat, which contained very high levels of about 2 mg methylmercury/kg.

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 of mercury.

The Japanese government recommends that children and pregnant women avoid eating dolphin meat on a regular basis.

[60] Legally consuming dolphin meat in the United States would be near impossible for most due to the Marine 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 as Alaska 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).

[62] Accidental bycatch in gill nets is common and poses a risk for mainly local dolphin populations.

[63][64] Dolphin safe labels attempt to reassure consumers that fish and other marine products have been caught in a dolphin-friendly way.

[65] Loud underwater noises, such as those resulting from naval sonar use, live firing exercises, and certain offshore construction projects such as wind farms, may be harmful to dolphins, increasing stress, damaging hearing, and causing decompression sickness by forcing them to surface too quickly to escape the noise.

Hundreds if not thousands of bottlenose dolphins live in captivity across the world, though exact numbers are hard to determine.

[68] The orca's intelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquaria and aquatic theme parks.

A dolphin rescued the poet Arion from drowning and carried him safe to land, at Cape Matapan, a promontory forming the southernmost point of the Peloponnesus.

He turned the oars into serpents, so terrifying the sailors that they jumped overboard, but Dionysus took pity on them and transformed them into dolphins so that they would spend their lives providing help for those in need.