Mammals Essays (1444 words) - Animal Physiology, Therapsids

Mammals Mammals have existed for the past 200 million years. According to fossil evidence, they evolved from a mammal like reptile group. These reptile ancestors were small, active carnivores. They were equipped with several specialized types of teeth. Their limbs were positioned more directly under the trunk as opposed to spreading out to the sides. Both of these characteristics are prominent features of mammals. For the past 70 million years mammals have been the dominant animals in terrestrial ecosystems. Because they are warm-blooded, they have an advantage over their reptilian ancestors. Despite their size differences, the great blue whale and the pygmy shrew have something in common: they are both members of a warm-blooded, air-breathing class of vertebrate animals known as Mammalia, or mammals. In many ways mammals are the most highly developed of all creatures. The term mammal explains one important way in which creatures in this class are set apart from other animals. It comes from the Latin mamma, which means, breast. Every female mammal has special glands, mammae that secrete milk. The females of all but the most primitive mammalian species are viviparous. This means they bear their young alive. The young are then fed with milk until they have grown enough to get food for themselves. Hair is a typical mammalian feature. In many whales, however, it exists only in the fetal stages of development. Another basic trait of mammals is their highly developed brains--the most complex known. Particularly well developed is their cerebrum, the part of the brain that controls memory and learning. The mammalian brain enables the young to learn from the experience of their elders. Since the young mammal is dependent on its mother for nourishment, a period of learning is possible. This in turn has brought about a degree of behavioral adaptability unknown in any other group of organisms. Whales, seals, and dogs are among the most intelligent mammals, but monkeys, apes, and humans are the most intelligent of all. Warm-bloodedness makes them capable of longer terms of sustained activity than cold-blooded organisms can undertake. This allows them to exploit environments that would be inhospitable to cold-blooded animals. The term warm-blooded does not mean that a mammal's body temperature is consistently warmer than that of the environment. In the hot tropics, in fact, the opposite is true. Warm-blooded animals, or endotherms, have an inner climate-control system that is physiologically maintained. Mammals can sustain a constant body temperature that is ideal for their bodily functions under most weather conditions. This requires a high rate of metabolism, and many attributes of mammals are related to its maintenance. A high metabolic rate requires a great deal of fuel in the form of food and oxygen. By being highly active and having strong limbs, mammals are able to generate heat and obtain large amounts of food. Their respiratory, circulatory, and digestive systems also need to be highly efficient to transform fuel into heat energy. For example, mammals have a secondary palate, which permits breathing while chewing or sucking. This feature assists in the delivery of large amounts of oxygen to the body tissues, where it is used to metabolize food. Food must be mixed with oxygen, or oxidized, for conversion into energy. Unlike cold-blooded creatures, whose body temperatures are dependent on the weather, mammals must produce a lot of energy to heat themselves. Accordingly, they need large quantities of oxygen. Mammals have strong lungs and, unlike any other class of animals, they have a breathing muscle called the diaphragm to pump large amounts of air into the body and force out carbon dioxide wastes. The circulatory system of mammals is also very efficient. Their red blood cells can transport more oxygen than those of any other animals, except birds. The mammalian heart is a complex four-chambered organ designed to keep unoxygenated blood and oxygenated blood from mixing. To accommodate this blood separation, mammals have a dual circulatory system. Mammals have a number of traits designed to conserve heat energy. Most mammals have body hair, which insulates by trapping air. Instead of a hairy coat, water-dwelling mammals such as dolphins and whales have a thick, insulating layer of fat.. Hair also serves a defensive and tactile role in mammals. The hair of hedgehogs