The Macdonald Encyclopedia of Mammals [antikvár]

THE VARIETY OF MAMMALS Mammals are the most diversified of all creatures living on earth today. They range from minute shrews to gigantic whales. The blue whale is the largest living mammal; a species of tiny bat from Thailand is the smallest. In addition, the variety of shapes, coloration, and behavioral patterns of mammals is greater than in most other animal classes. Mammals have colonized every environment. They have mastered the techniques of swimming and burrowing, and have achieved true flight. They live in equatorial and polar regions alike, and feed on whatever food resources are available. There is no doubt that they have taken on a predominant role. Perhaps surprisingly, there are not many mammals—approximately 4,000 species, compared with about 7,500 species of reptiles and amphibians or 8,600 species of birds. Mammals represent a very advanced stage in the long process of animal evolution: the complexity—physiological and behavioral—of an organism such as a mammal is unmatched by that of any other animal. Over relatively short periods of geologic time, when compared with the long periods needed by other animal classes, mammals have assumed widely varied ecological roles, taking over from more ancient forms of animal life. We ourselves—that is, mankind (Homo sapiens)—are also mammals and naturally share with other mammalian families our complex anatomy and physiology, as well as much in our behavioral patterns. And precisely because of his natural affinity with other mammals, man has selected from them those animals which are now his closest companions, such as the domestic dog and cat. A variety of species have taught us about ourselves through observation and scientific experimentation, Man has also destroyed countless fellow mammals under the banner of "sport." And finally, mammals have found themselves burdened with the task of providing man with his major food resources. Human progress has often been at the expense of our fellow mammals. It is thus quite natural that we should have a special regard for these creatures. Many mammals are not readily seen in the daytime, nor are they easy to observe and study. A number of species are known only from specimens lodged in museum cabinets; we have no knowledge of their lives. Many mammals have only a neutral coloration, and so fail to attract the notice of laymen. The result is that most of us are acquainted only with the striking or sensational species, and it is left to the specialists to fill in the gaps in our information bank. Before we discuss the structure of a mammal and its classification, let us first see how these animals came into being. THE ORIGIN AND EVOLUTION OF MAMMALS The origin of the first mammals dates back to evolutionary efforts made by certain reptiles about 250 million years ago. Mammals, like birds, owe their presence on earth to the remarkable range of forms that reptiles displayed for literally 10