Bottlenose dolphin

The Bottlenose Dolphin is gray, varying from dark gray at the top near the dorsal fin to very light gray and almost white at the underside. This makes it hard to see, both from above and below, when swimming. Its elongated upper and lower jaws form what is called a rostrum, or beak-like snout, which gives the animal its common name. The real, functional, nose is the blowhole on top of its head; in fact the nasal septum is visible when the blowhole is open. Its face shows a characteristic "smile" but that does not mean it is happy since it is unable to move its jaw to any other position.

Adults range in length from 2 to 4 metres (6 to 13 ft) and in weight from 150 to 650 kilograms (330 to 1430 lb)^[2] with males being on average slightly longer and considerably heavier than females; however, in most parts of the world the adult's length is about 2.5 m (8 ft) with weight ranges from 200 to 300 kg (440 to 660 lb). The size of a dolphin appears to vary considerably with habitat. Those dolphins in warmer, shallower waters tend to have a smaller body than their cousins in cooler pelagic waters. For example, a survey of animals in the Moray Firth in Scotland, the world's northernmost resident dolphin population, recorded an average adult length of just under 4 m (13 ft) compared with a 2.5 m (8 ft) average in a population off the coast of Florida. Those in colder waters also have a fattier composition and blood more suited to deep-diving. Most research in this area has been restricted to the North Atlantic Ocean, where researchers have identified two ecotypes^[3].

The flukes (lobes of the tail) and dorsal fin are formed of dense connective tissue and do not contain bones or muscle. The animal propels itself forward by moving the flukes up and down. The pectoral flippers (at the sides of the body) are for steering; they contain bones clearly homologous to the forelimbs of land mammals (from which dolphins and all other cetaceans evolved some 50 million years ago). In fact a Bottlenose Dolphin was recently discovered in Japan that has two additional pectoral fins, or "hind legs," at the tail, appearing to be about the size of a human's pair of hands.^[4] Scientists believe that a mutation must have caused the ancient trait to reassert itself as a form of atavism.

Female Bottlenose Dolphins live for about 40 years, whereas males rarely live more than 30 years.