Dolphin

A dolphin is an aquatic mammal within the infraorder Cetacea in the order of toothed whales. There are 40 extant species of dolphin in various shapes and sizes from the 1.7 metre-long Maui's dolphin to the largest representative, the 9.5 metre-long orca.

Various species of dolphins exhibit sexual dimorphism such as the males are larger than females and some such as the orcas have extra features, as males have longer and straighter dorsal fins than the females. They have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, some dolphins can briefly travel at speeds of 29 kilometres per hour (18 mph) or leap about 9 metres (30 ft). Dolphins use their conical teeth to capture fast-moving prey whether alone or in a group. Dolphins feed largely on fish and squid, but a few, such as the orca, feed on large mammals such as seals.

Dolphins are known to teach, learn, cooperate, scheme and grieve. the neocortex of many species is home to elongated spindle neurons that, prior to 2007, were known only in hominids. In humans, these cells are involved in social conduct, emotions, judgment, and theory of mind. Cetacean spindle neurons are found in areas of the brain that are analogous to where they are found in humans, suggesting that they perform a similar function.

Dolphins are sometimes hunted in places such Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they also face threats from bycatch, habitat loss, and marine pollution. Dolphins have been depicted in various cultures worldwide. Dolphins are also sometimes kept in captivity and trained to perform tricks.

Trivia

 * Keeping dolphins in captivity has long been a source of great controversy, and although animal husbandry conditions have improved greatly since the 1800s, many animal rights activists still view dolphinariums as cruelty to animals.
 * As mentioned in Chapter 19, visitors of the Tokuma Marine Park are allowed to pet the dolphins after the dolphin show. In real life, however, this would be expressly forbidden in most dolphinariums, since there is a risk that humans could transmit diseases to the dolphins by touching them. Above all, baby dolphins are particularly endangered because, due to their weakly developed immune system, they can often contract fatal diseases.
 * In many stories and myths, dolphins are portrayed as friendly and helpful and sometimes considered opponents of "evil" sharks, but this also caused many people to underestimate the potential danger that dolphins themselves can pose. Although dolphins are rarely aggressive, they can also attack humans in stressful situations and these attacks can also be fatal. This risk is exacerbated by the fact that many people misinterpret dolphin behaviour as "friendly" when they are actually expressing disturbance or aggression.