Cetaceans And Evolution :: essays research papers

CetaceansThere are umpteen forms of cetacean life subsisting in the worlds waters. How an why they came into existence is uncertain, alone there have been many a(prenominal) theories. Some say that dolphins are aquatic forms of goats, and others believe they evolved just like everything else, from a single cell, and non from an actual multi-cellular being. Because most cetaceans have any(prenominal) vestigial structures such as under-developed os coxae, the former of these two theories carcass prevalent in mostresearchers minds.The theory that cetaceans evolved from a goat-like being is not at all farcical. The similarities between the skeletal systems are more than coincidental. The only difference is that the cetaceans adapted to a marine lifestyle. The front limbs became modified as paddle-shaped flippers, the bones of which are still reminiscent of jointed limbs and digits, but the back(prenominal) limbs were lost. The broad horizontal tail flukes that provide the main p ropulsive punch bear no anatomical connection to the lost hind limbs, but are a seperate and distint development. They contain no bone, and owe their firm and besides flexible shape to underlying fibrous elastic tissue. The body is enveloped in a thick layer of blubber that aids in bouyancy, helps to keep open body heat, and is a source of stored energy. A cetaceans spit out is free of sweat glands, oil glands, or h channelize, and feels much like smooth, nonsensical rubber to the touch.Cetaceans, like other mammals, have lungs. They breathe line of credit finished a single nostril, or pair of nostrils, located on the upper side of the head but contrary to a popular image, they do not spout water when they exhale. The visible spout, the size and shape of which is unique to many species, is simply water vapor in the lungs and a small tally of water present in the depressionaround the blowhole, which is blown into the air as th cetacean exhales.A number of physiological adapt ations alter whales to perform deep dives. First, they have a larger blood garishness than land mammals of comparable size and weight, and they also have a greatly increased capacity to store oxygen in their blood and tendon tissue. Second, each breath provides an 80 to 90 percent renewal of air in the whales lung, compare with only 10 to 20percent in most land mammals. Third, cetaceans have a subway to the metabolic by-product carbon-dioxide, the buildup of which in the tissues, rather than the lack of oxygen, triggers the involuntary breathe response of most mammals.