Chap. 37 



MAMMALS AND MANKIND 



759 



Representative Groups of Placental Mammals 



One or another of these mammals is adjusted to all the major phases of 

 environment, air, water, and land. They can live in arctic, temperate, or tropi- 

 cal climates; they are fitted to manifold special niches in swamps and plains; 

 to life in tropical forests and rocky mountain slopes — on deserts and in the 

 ocean. An animal's diet, habitat, and general way of living are reflected par- 

 ticularly in the character of its locomotor appendages and in the number and 



Fig. 37.7. Kangaroo (Macropus). The 

 joey is leaning out of the pouch or marsu- 

 pium. At this age the joey jumps out of the 

 pouch, crops grass as its mother does and 

 clambers in again. Koalas and kangaroos 

 are the most pictured of the marsupials of 

 Australia, but there are many other marsu- 

 pials — among them pouched rats, moles, ant- 

 eaters and flying opossums. They have re- 

 tained characteristics that were general in 

 mammals more than 70 million years ago. 

 (Courtesy, Young: The Life of The Verte- 

 brates. Oxford, England, The Clarendon 

 Press, 1950.) 



type of its teeth. The placental mammals are arranged in orders, the num- 

 ber differing slightly with the valuations given by the classifier. Groups called 

 orders in one system may be suborders in another. The names, general habitat, 

 and diet, are given here for the orders to which the better-known placental 

 mammals belong. 



Insectivora — Moles and Shrews (Fig. 37.9). Moles are stout-bodied bur- 

 rowers with pointed noses, hardly visible eyes and ears, and a hunger for 

 worms and insects. Their total length is five to nine inches. Shrews are the 

 smallest of North American mammals, high strung, constantly moving, secre- 

 tive, common but seldom seen, and fierce in their attacks on insects and mice. 

 The length of various species of shrews ranges from three to six inches. 



Chiroptera — The Only Flying Mammals (Fig. 37.10). The Chiroptera in- 

 clude the large fruit bats of the Eastern Hemisphere and small ones, that are 

 chiefly insectivorous. The wings are formed of webs of skin and instead of be- 

 ing supported by a single long finger as in the wings of ancient reptiles, those 

 of bats are supported by nearly the whole hand. Bats are skilled night flyers, 

 avoiding all obstacles. As they fly, they constantly utter cries inaudible to the 

 human ear. These are reflected back from objects as ultrasonic echoes that are 

 detected by the bats (Fig. 17.8). 



Rodentia — Gnawing Mammals. This large group includes the woodchucks 

 and ground squirrels, chipmunks, squirrels, mice, rats, muskrats, porcupines, 



