Dolphin

Dolphins are aquatic mammals that are intimately related to whales and porpoises.

Dolphins, along with whales and porpoises, are thought to be descendants of terrestrial mammals, the majority likely of the Artiodactyls order. Dolphins entered the water roughly fifty million years ago. Dolphins have a streamlined fusiform body, adapted for fast swimming. The essential coloration patterns are shades of gray with a light underside and a distinct dark cape on the back. It is often mutual with lines and patches of different hue and contrast.

Modern dolphin skeletons have two little; rod-shaped pelvic bones thought to be vestigial hind legs. In October of 2006, a strange Bottlenose Dolphin was captured in Japan that had small fins on each side of the genital slit, which scientists believe to be a more pronounced development of these vestigial hind legs.

The head contains the melon, a surrounding organ used for echolocation. In many species, the jaws are elongated, forming a distinct beak; for several species like the Bottlenose, there is a curled mouth that looks like a fixed smile. Teeth can be very numerous (up to two hundred and fifty) in several species.

The dolphin brain is huge and has a highly structured cortex, which often is referred to in discussions about their higher intelligence. A recent theory however disputes the existence of a neural basis for dolphin intellect, suggesting instead that the huge brain is only an adaptation to living in cold water. This theory has not found extensive acceptance.

In 1933, three irregular dolphins were beached off the Irish coast; these appeared to be hybrids between Risso's Dolphin and the Bottlenose Dolphin. This mating has since been repeated in imprisonment and a hybrid calf was born. In captivity, a Bottlenose Dolphin and a Rough-toothed Dolphin produced hybrid offspring. Usually, Spinner Dolphins have sometimes hybridized with Spotted Dolphins and Bottlenose Dolphins. Bands of males of one dolphin species often mate with lone female Spinners. Blue Whales, Fin Whales and Humpback Whales all hybridize usually. Dall's Porpoises and Harbor Porpoises also normally hybridized. There has also been a report of a possible hybrid between a beluga and a narwhal; however these are not true dolphins.