Dolphins have a streamlined fusiform body

In 1933, three strange dolphins beached off the Irish coast; they appeared to be hybrids between Risso's and bottlenose dolphins.[15] This mating was later repeated in captivity, producing a hybrid calf. In captivity, a bottlenose and a rough-toothed dolphin produced hybrid offspring.[16] A common-bottlenose hybrid lives at SeaWorld California.[17] Other dolphin hybrids live in captivity around the world or have been reported in the wild, such as a bottlenose-Atlantic spotted hybrid.[18] The best known hybrid is the wolphin, a false killer whale-bottlenose dolphin hybrid. The wolphin is a fertile hybrid. Two wolphins currently live at the Sea Life Park in Hawaii; the first was born in 1985 from a male false killer whale and a female bottlenose. Wolphins have also been observed in the wild.[19]
Evolution and anatomy



The anatomy of a dolphin, showing its skeleton, major organs, tail, and body shape


A skin-skeletal preparation at the Horniman Museum


Pacific white-sided dolphin skeleton (missing pelvic bones), on exhibit at The Museum of Osteology, Oklahoma City, Oklahoma
Evolution
See also: Evolution of cetaceans
Along with whales and porpoises, dolphins are descendants of terrestrial mammals, most likely of the Artiodactyl order. The ancestors of the modern-day dolphins entered the water roughly 55 million years ago, in the Eocene epoch.[20]


Hind limb buds are apparent on an embryo of a spotted dolphin in the fifth week of development as small bumps (hind limb buds) near the base of the tail. The pin is approximately 2.5 cm (1.0 in) long.
Modern dolphin skeletons have two small, rod-shaped pelvic bones thought to be vestigial hind limbs. In October 2006, an unusual bottlenose dolphin was captured in Japan; it had small fins on each side of its genital slit, which scientists believe to be an unusually pronounced development of these vestigial hind limbs.[21]
Anatomy
Dolphins have a streamlined fusiform body, adapted for fast swimming. The tail fin, called the fluke, is used for propulsion while the pectoral fins, together with the entire tail section, provide directional control. The dorsal fin, in those species that have one, provides stability while swimming. Though varying by species, basic coloration patterns are shades of grey, usually with a lighter underside and often with lines and patches of different hue and contrast