Dolphins (Delphinidae)

Dolphins (Delphinidae) are a family of marine mammals which have a streamlined body and a beak-like snout. They dwell in the seas and oceans of the world. They belong to the order Cetacea, which also comprises the whales and porpoises. There are nearly forty species of dolphins swimming the salt waters of the world. Despite its name, the killer whale also belongs to the Delphinidae family. Dolphins range in size from 1.8 m to 9.8 m in length, with the Maui's dolphin being the smallest species and the killer whales the largest one. However, all of them share the following physical characteristics: a large falcate dorsal fin (curved and tapering to a point), which is set near the middle of the back; two flippers on the underside, located towards the head; a tail fin, which is disposed horizontally, like the whales'; conical teeth; and a noticeable beak-like snout. As mammals, they have the same body temperature that we, humans, have; 37° C (98.6° F). This is the reason, their different species can be found world-wide, both in the northern and southern hemisphere.

The common dolphin (Delphinus delphis) is the most plentiful species of the family Delphinidae. They are found in every ocean of the world. It is a close relative of the bottlenose dolphin, which is the second most abundant species. They both inhabit warm and temperate seas world-wide. However, the bottlenose dolphin is the most intelligent of all mammals of the order cetacea. Its brain is larger than the chimpanzee's. It can easily be trained as it learns quickly to perform important challenging tasks, such as locating and moving marine mines. In some coastal regions, the bottlenose dolphins cooperate with local fishermen by driving schools of fish into their nets. They can hybridize with other species of dolphins. With 4 m in length and a weight of 300 kg, bottlenose dolphins are larger and heavier than the common dolphin, whose average length is 2.5 m.

Many species of dolphins are found in the warmer oceanic waters of the tropic zones. However, some species, like the right whale dolphin, prefer colder climates. Some have a global distribution, like the killer whale. Oceanic dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, like the 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. The dolphin ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. Dolphins send out high frequency clicks from an organ known as a melon. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. This allows dolphins to produce biosonar for orientation.

Dolphins have outstanding swimming skills as they can breach thoroughly (leap completely out of the water) and then dive down back into the water as they curve their bodies. They can also spin around as they come out of the water. Along with the killer whale, they are the fastest marine mammal, reaching a maximum speed of up to 65 km/h (39 mph). Measuring dolphin speed can be challenging, but researchers use various methods such as radar, acoustic tracking, and video analysis to study their movements. One of the most important parts of a dolphin’s anatomy for swimming is their tail and flukes. The tail flukes is arranged horizontally instead of vertically as is case in fish. The dolphin tail is composed of powerful muscles that allow its body to move through the water. Therefore, dolphins are stronger and faster than a shark, which is a fish.

Above, the bottlenose dolphin, the smartest species.

The common dolphin, which is the most abundant species of dolphin.