FACTS AT YOUR FINGERTIPS ENDANGERED ANIMALS MAMMALS OF THE NORTHERN HEMISPHERE BROWN BEAR BOOKS
What is a Mammal mammals mammals typically have a high body temperature usually about 95 to 100 F 35 to 38 C They are homeothermic meaning that this temperature is normally kept fairly constant throughout the animal’s life Mammals are also referred to as endotherms meaning that the warmth is generated internally making them largely independent of external sources of heat such as the warmth of the sun Their offspring are born as active babies and fed on milk secreted by the mammary glands of the mother Echidnas and the platypus are exceptional in producing eggs but still nourishing their young with milk Parental care which sometimes lasts for years is normal among mammals and allows the offspring to learn from older animals Generally families are small and the young are well looked after to achieve a higher survival rate Many species also live in social groups in which individuals cooperate to raise their young more successfully Most mammals have a hairy or furry coat which helps insulate them and maintain their high body temperature Some whales for example are nearly hairless as an adaptation to their particular way of life but insulation is then provided by large amounts of fat blubber under the skin In conjunction with their warm body mammals also have a very efficient blood circulatory system It works faster and at higher pressures than in all other animals except birds Endothermic homeothermy warm bloodedness and an efficient blood system enable muscles and nerves to work faster speed up digestion of food help babies grow more rapidly and generally assist mammals in living a much more active life than most other creatures Variations on a Theme The basic mammal body plan including four feet each with five toes has been modified to allow the 4 development of highly efficient diggers runners swimmers and fliers The teeth are also specialized to cope with many different kinds of food from meat to nuts leaves fish grass blood and insects These characteristic features of mammals enable them to live in a wide variety of habitats more independently of their surroundings air temperature for example than any other animals Mammals occur on all the continents in the polar regions deserts mountaintops and jungles Some can make prolonged dives into deep oceans Mammals can survive successfully in a wider diversity of habitats than any other animal group of comparable size One species our own has even left this world to visit another no other animal ever did that Mammals and People Some mammals have become very abundant and widespread Many such as horses dogs cattle and sheep have also played a key role in the success of our own species helping humans in their conquest of the planet by providing us with meat milk leather transportation and muscle power Some assist in medical research to aid our own species but others are significant pests and carriers of disease The History of Mammals The first mammals evolved when dinosaurs ruled the world about 100 million years ago Mammals are therefore a comparatively new group of animals many others have a much more ancient origin Reptiles for example first appeared over 200 million years earlier The first mammals were small and insignificant creatures that looked like today’s solenodons and gymnures From simple beginnings mammals have evolved into a wide assortment of species based on shared features and now include the blue whale the largest animal ever The smallest mammal is the
WHAT IS A MAMMAL The earliest mammals were small inconspicuous insect eaters like the long extinct Megazostrodon above Over the last 200 million years mammals have come to dominate the planet and now the group includes animals as diverse as bats kangaroos sea otters left and humans danger to domestic animals Large mammals are also in danger simply because of their size American bison pp 46 47 for example take up a lot of space and need a great deal of food every day A bison might eat the same amount as say two cows but the same Etruscan shrew at about 2 grams it is smaller than many beetles Over the last one to two million years enormous changes have taken place in the variety of mammal species present in different parts of the world Many have become extinct or been reduced to critically small numbers Why Are Mammals at Risk In historic times mammals have suffered heavily from attacks by humans particularly the larger and fiercer species such as the tiger pp 10 11 gray wolf pp 20 21 and polar bear pp 24 25 that were considered to be a threat to our own survival or a vegetation cannot feed both The same patch of ground cannot grow grass for bison while at the same time providing grazing for domesticated animals or producing crops for people Around the world the expansion of farmland has pushed wild animals back into less suitable areas and their numbers have dwindled in the example of the American bison dramatically In other parts of the world the wild mammals elephants for example have been forced to steal from the crops planted on the land they used to occupy They are then called pests and eliminated with guns traps and poisons Even using more humane forms of control such as putting up fences 5
