Dolphins range in size from the 1.7 m (5.6 ft) long and 50 kg (110 lb) They have streamlined bodies and two limbs that are modified into flippers.  Some dolphins can travel at 55.5 km/h (34.5 mph). They use their conical shaped teeth to capture fast moving prey and have well-developed hearing which is adapted for both air and water. This is so well developed that some can survive even if they are blind. Some species are well adapted for diving to great depths. Under the skin, they have a layer of fat (blubber), to keep warm.

Although dolphins are widespread, most species prefer the warmer waters of the tropical zones. Dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, like seals. Male dolphins typically mate with multiple females every year, but females only mate every two to three years.