Dolphins are cetaceans, which means that they are marine mammals that are in the same class as whales and porpoises. They are known for being extremely intelligent and there are many accounts of them helping swimmers, surfers and victims of shipwreck to get to safety, even when threatened by predators, such as sharks.
There are nearly 40 different dolphin species. Interestingly, some species are defined as being whales but are, in fact, dolphins. These are the 1) melon-headed whale, 2) killer whale (or orca), 3) pygmy killer whale, 4) false killer whale, 5) short-finned pilot whale and 6) long-finned pilot whale.
Dolphin under water playing with a some seaweed.
In general, dolphins can measure anything from four feet (1.2 metres) to 30 feet (9.5 metres). This indicates how very diverse this class of marine mammals is. They are all carnivores, usually feeding on soft squid and fish. Dolphins are adept at hunting and have many sharp teeth to seize their prey.
Dolphins are found in oceans and fresh waters all around the world. However, they tend to prefer the shallower waters of continental shelves, which means that they are frequently spotted from the shore as they play in the surf and leap from the cool water.
The body shape of the dolphin is cylindrical, enabling the animal to cut through the water at high speeds with ease. They use the tail fin to propel them forward, and the dorsal fin performs a balancing function. The melon shape of the head is an important part of the anatomy, as it is integral to their echolocation (using sound to perceive objects around them, including predators). The sound is conducted from the water, via the jawbone, into the middle ear. Therefore, the teeth act as tiny antennae that receive the sound and direct the animal to the precise source.
Like other cetaceans, dolphins breathe through a blowhole on the tops of their heads, which directs fresh air to and from the lungs. They have excellent eyesight, both in the dense, moving water and outside of it. They are believed to have no sense of smell judging from the lack of olfactory nerves.
Notably, dolphins are known to be able to survive and recover from severe wounds. Infection of even large wounds is rare. Their mechanism for healing remains a mystery to scientists.
Dolphins are sociable, inquisitive and intelligent. As a result, they often leap out of the water near and around boats to catch a glimpse of the goings on outside their watery world. Dolphins are often trained to perform tricks and even very useful functions. They have been used in the military as well as for treating the sick and helping the handicapped. They are also social with one another. They travel and hunt together in pods. These pods can comprise just a few individuals, but frequently hundreds of dolphins. They establish very close bonds with one another, assisting and protecting each other fiercely. Dolphins are the only species, other than human beings, that participate in sexual relations for purposes other than breeding. Rather, they may have sex with one another simply to strengthen bonds. Homosexual behaviour has been noted amongst dolphins.
Dolphins may be aggressive toward one another at times, usually caused by an altercation between two companions or in competition for the attention of a female. Aggression has been noted during times of sexual activity too. This may be limited to males or may include the female.
The only real enemy of dolphins is the human being. Sadly, they continue to be hunted for their meat, which is considered a delicacy in many lands, but is also sometimes included in tinned fish and exported all over the world under the guise of being tuna. Another major problem that dolphins face are fishing nets. They unknowingly swim into these, become entangled and drown. Pollution and chemical waste are also threats to dolphins (and other marine animals), who become poisoned or hurt by harmful foreign materials in the water.