Humans have always found dolphins to be enchanting creatures. Ever since the days of the first seafarers, they have been the subject of numerous works of art, literature, and myth. They are among the most intelligent of animals, as some species have brain to body mass ratios equal to that of a human being. They are also mammals, having evolved from land-faring creatures tens of millions of years ago. They are known for their extremely gregarious behavior. Dolphins belong in the kingdom Anamalia; phylum, corata; class mammalia; order, cetacean; sub-order, odonteceti; family, delphinidea; genus, delphinus; and species, delphis.
Dolphins are very social creatures and use interaction for the purpose of hunting, defense, and reproduction. Dolphins are normally found in groups of families for 2-40 members called pods. Larger groups in the hundreds have been reported and are referred to as herds. They are carnivorous, predatory mammals and feed on fish, squid, octopus, cuttlefish, crabs, shrimp, and lobsters. They are regularly hunted by sharks, killer whales and in some places, humans. Humans are the most dangerous predator of the dolphin and have decimated their existence. We as humans have been known to kill dolphins for their meat, their fat, even for being pests to fishermen.
Dolphins, like all mammals bear live young and usually only give birth to one calf at a time, rarely giving birth to twins. The mothers usually nurse and care for their calf for one to three years after the calf is born. After the nursing stage, mothers usually stay with their young for up to eight years. The dolphin usually has a lifespan of about 30 years, depending on their particular location and its ecosystem. For example, in the Gulf of Alaska there are few dolphin species, one of which is the pacific white sided dolphin. This particular dolphin has a short, rounded beak with about 30 curved teeth in each side of the jaw, most likely specialized for eating clams and other shelled mollusks that populate that area. They are very energetic and are often seen leaping, belly flopping and summersaulting in the water. They are attractively marked with a black back, gray sides and white stripes spanning from their eyes to the tail, like seen below.

Pacific white–sided dolphin

The dorsal fin is tall and sharply hooked; flippers are small and rounded at the tips, and its fluke or tail has a notched center. They are seven to eight feet in length and weigh up to 300 pounds. It is said that dolphins, whales, and porpoises are all related. Fossil evidence has been found from the early Eocene epoch that indicates early dolphins were already aquatic 45 to 50 million years ago. It is believed that animals that spent a great deal of time looking for food around water areas went through a amphibious stage before becoming committed to water. Once in the water records show that by changes in their teeth it took millions of years for true cetaceans to develop.

Present day dolphins have come a long way from the once amphibious animal it is believed to have evolved from. Anatomically, dolphins’ bodies have become streamlined to move more efficiently through the water. Their front limbs evolved into flippers and their powerful tail is their main propulsion mechanism. They have a thickened body with a raised head that caused the vertebrae in the neck to fuse together. Instead of a major blood supply to the brain on the outside of the neck, the dolphins blood flows through an artery in the vertebrae that provides a constant supply of blood, which is most essential when diving into the depths of the ocean. The dolphin’s skin is extremely smooth, hairless, thick, and lacks glands. This skin is kept smooth by constantly sloughing off and being replaced. On average a dolphins skin is replaced at a rate nine times faster than a human, and in the case of the bottle nose dolphin, the outermost layer of skin is replaced every two hours.

(Animalfiles.com) Dolphins tend to rely on their sense of hearing to survive. They are said to have good eyesight, but in the darkness of the ocean, other senses have had to develop for survival. The shape of the dolphins melon (fatty tissue in front of the blow hole) acts as a lens to focus sound when the dolphin produces high pitched clicks for echolocation. When the sound comes back the small bone under the chin, called the pan bone, receives the sonic report and stimulates the brain via the inner ear. With echolocation the dolphin can judge distance by measuring the time between emiting the clicks and the return. With this amazing skill, dolphins can dertermine the size, shape, direction of movement, and the distance of objects in the water. The doliphin has adapted quite well to its life as a fully aquatic mammal and has evolved the ideal shape and skill to breed successfully and thrive in any marine environment. The fascinating skill of echolocation gives the dolphin a huge advantage when feeding in the darkness of the ocean. Dolphins are ver energetic, kind, and smart animals and are arguably one of the most loved mammals by people.

References
Animal Filies.com. (n.d.). Retrieved 2012, from Anatomy of a Dolphin: http://www.theanimalfiles.com/anatomy/dolphin_anatomy.html

Dolphin Facts and Information. (n.d.). Retrieved 2012, from dolphins-world.com: http://www.dolphins-world.com/Pacific_White_Sided_Dolphin.html

Dolphins: The Oracles of the Sea. (n.d.). Retrieved from ThinkQuest: http://library.thinkquest.org/17963/man-and-dolphin.html

Understanding Dolphins. (n.d.). Retrieved 2012, from Understandingdolphins.com: http://understanddolphins.tripod.com/dolphinevolution.html