AskEssays.com - Discover essay samples

Cetaceans and evolution

4.9 of 5.0 (51 reviews)

Contains
415 words
Category
Science

Cetaceans and evolution Page 1
Cetaceans and evolution Page 2
The above thumbnails are of reduced quality. To view the work in full quality, click download.

Cetaceans and evolution


Cetaceans



There are many forms of cetacean life living in the worlds waters. How an why they came into existence is uncertain, but there have been many theories. Some say that dolphins are aquatic forms of goats, and others believe they evolved just like everything else, from a single cell, and

not from an actual multi-cellular being. Because most cetaceans have some vestigial structures such as under-developed os coxae, the former of these two theories remains prevalent in most

researchers 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 hind limbs were lost. The broad horizontal tail flukes that provide the main propulsive thrust 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 yet flexible shape to underlying fibrous elastic tissue. The body is enveloped in a thick layer of blubber that aids in bouyancy, helps to preserve body heat, and is a source of stored energy. A cetacean's skin is free of sweat glands, oil glands, or hair, and feels much like smooth, wet rubber to the touch.

Cetaceans, like other mammals, have lungs. They breathe air through a single nostril, or pair of nostrils, located on the top 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 amount of water present in the depression

around the blowhole, which is blown into the air as th cetacean exhales.

A number of physiological adaptations enable whales to perform deep dives. First, they have a larger blood volume than land mammals of comparable size and weight, and they also have a greatly increased capacity to store oxygen in their blood and muscle tissue. Second, each breath provides an 80 to 90 percent renewal of air in the whale's lung, compare with only 10 to 20

percent in most land mammals. Third, cetaceans have a resistance to the metabolic ...

You are currently seeing 50% of this paper.

You're seeing 415 words of 829.

Keywords: cetaceans evolution, how did cetaceans evolve, who are cetaceans believed to evolve from

Similar essays


Endocrine Disruptors

During recent years, numerous newspaper and magazine articles have suggested that humans may be at risk because small amounts of well known environmental contaminants, such as dioxin, PCBs and DDT, can affect hormone levels. Hormones are produced by the endocrine system as regulators of biological function in target organs. Because hormones pla...

167 reviews
Download
Fishes

There are two classes of fishlike creatures in the Chordate Phylum. The first is Chondrichthyes Class, which comprises mainly of Sharks and Rays. The seconds is the common Bony fishes of the class Ostechithyes. The apparent similarities between each speech are only skin deep. They have similar dapperly solely because of convergent evolution and...

19 reviews
Download
Migraines

Migraine headaches are the result of a disturbance in the neurochemistry of the central nervous system. They are relatively common, affecting three times as many women as men. Migraine sufferers typically report a definite pattern to their headaches, and they can report what stimuli bring them on. Most migraine sufferers experience...

62 reviews
Download
Gas laws (cemistry)

Chemistry Independent Study: Gas Laws Gas Laws Since the days of Aristotle, all substances have been classified into one of three physical states. A substance having a fixed volume and shape is a solid. A substance, which has a fixed volume but not a fixed shape, is a liquid; liquids assume the shape of their container but do not nece...

198 reviews
Download
From legend to science the health benefits of tea

From Legend to Science: the Health Benefits of Tea Throughout the world, tea and coffee rival each other as mankind's most popular brewed beverages. For thousands of years, however, tea has had one great advantage over coffee: it is believed to have a wide range of medicinal properties. In his book, Tea in China, John C. Evans states that ''...

34 reviews
Download
Atsisiųsti šį darbą