As dolphins are mammals with a quite different skeletal structure to fish, they use up and down strokes of their tail to swim, unlike fish which use side to side movements. In fact, there are still remnants of their land dwelling heritage in their skeletal structure. For example, they have forelimbs, but they have been adapted into pectoral fins. Like humans, these consist of a humerus with a ball and socket joint, a radius, an ulna, and a complete hand structure, including five phalanges, or finger bones. There have no hind limbs, but vestigial skeletal remains can sometimes be observed.
Although an adult dolphin has no hair, new born dolphins have whiskers on their rostrum which soon fall out.
Dolphins breathe air into their lungs via their blowhole which is located on the top of their body at the rear of the head. They can also use their blowhole to create sounds. Dolphins must surface to breathe regularly, or they will drown; this is why dolphins caught in fishing nets so frequently die. Although some dolphins can hold their breath for fifteen minutes or more, when they are swimming normally they will usually breathe much more frequently, typically breathing about every six or seven minutes.
Bottlenose dolphins have been recorded as being able to dive to over 300 metres, but they usually choose to dive much shallower than that, with many coastal communities spending most of their time in less than ten metres depth. When it dives, a dolphin slows its heartbeat as little as twelve beats per minute.
Dolphins have very acute hearing, and a brain that is much better able to process sounds than the human one. Surprisingly, they have much better vision than one might expect of a creature that uses echolocation as its main way of observing its world. They also have particularly good night vision. Dolphins have a very limited sense of smell.