296 



SUBPHYLUM VERTEBRATA: 



the head and has a valve to prevent water intake; eyes 

 are adapted for under water; a special group of 

 organs detect and recognize distant objects the ani- 

 mals can neither see nor hear; teeth are specialized 

 for grasping or filtering; the air sacs of the lungs have 

 muscles to prevent lung collapse under great outside 

 pressure; and the blubber is a very thick layer. 



Arboreal mammals have a way of life that allows 

 them to escape many possible predators and to use 

 another source of food. However, modifications for 

 tree life are not as marked as those for aquatic life. 

 In fact, many mammalian orders have arboreal repre- 

 sentatives. The best-adapted species are not found in 

 the United States; they are tropical animals. The 

 New World monkeys have delicate hands, long limbs, 

 and a long, prehensile tail that makes them very 

 successful in trees. Another tree-adapted group, the 

 sloths, have long toenails that are used to suspend 

 the animals upside down from tree limbs. Sloth fur 

 grows toward the backbone so it hangs toward the 

 ground when the animals are hung upside down. 

 Also, these animals often have camouflage in the form 

 of green and blue-green algae growing on their fur. 



No United States mammal is more than partly 

 arboreal. The tree squirrel, for example, has only 

 hand-like feet with long and flexible toes and sharp, 

 strong claws, and a long bushy tail that is useful in 

 breaking falls. Our flying squirrels have the same 

 adaptations plus two folds of skin (from forelimbs to 

 hindlimbs) that enables them to glide for some dis- 

 tance. In flying squirrels the tail is effective as a 

 rudder during the gliding process. 



Burrowing mammals show a range of modifications 

 for their way of life. Animals such as ground squir- 

 rels, kangaroo rats, and prairie dogs are only partly 

 modified. However, moles and gophers are examples 

 of almost strictly burrowing, or fossorial, mammals. 

 Their eyes are reduced, as are the external ears, but 

 the senses of smell and touch are magnified. In addi- 

 tion, the limbs are short and strong and the claws are 

 strengthened for digging. 



Arctic animals acquire dense coats and thick fat 

 or even blubber. In many the color matches seasonal 

 changes in environment — many hares, weasels, foxes, 

 and other animals are dark in the summer and white 

 in the winter. Also, the external parts such as the 

 ears and tail often become smaller, thereby presenting 

 less surface area to give off heat. Finally, arctic mam- 

 mals like reindeer and musk-oxen crowd together to 

 conserve heat during periods of extreme cold. The 



exhaled air of these animals often creates clouds that 

 can be seen from some distance. 



Many desert mammals have specializations that 

 aid water conservation. Although all animals have 

 the ability to obtain water from even dry food, a 

 process associated with body metabolism, some 

 desert mammals have this highly developed. For 

 example, kangaroo rats in the wild probably do not 

 drink water. Many desert animals avoid the heat by 

 burrowing, being nocturnal, and aestivating during 

 the hottest and driest part of the year. Many desert 

 species are seed gatherers and have cheek pouches to 

 aid in this purpose. Finally, these animals tend to be 

 jumping types, perhaps an aid to escape from pred- 

 ators in a fairly open situation. 



SELECTED READINGS 

 \ERTEBRATES, GENER.AL 



Blair, W. F. at al., 1957. Vertebrates oj the i'nited Stales. 

 McGraw-Hill Book Co., New York. 



Orr, Robert T., 1961. Vertebrate Biology. W. B. Saunders 

 Co., Philadelphia. 



Vessel, M. F., and E. J. Harrington, 1961. Common .\ative 

 .Animals. Chandler Publ. Co., San Francisco, Calif. 



Young, J. Z., 1950. The Life of Vertebrates. Oxford Univer- 

 sity Press, New York. 



FISHES 



Axelrod, H. R., and L. P. Schults, 1955. Handbook of Trop- 

 ical .Aquarium Fishes. McGraw-Hill Book Co., New 

 York. 



Barnhart, P. S., 1936. Marine Fishes of Southern California. 

 University of California Press, Berkeley, Calif. 



Beebe, W., and J. Tee- Van, 1933. Field Book of the Shore 

 Fishes of Bermuda. J. P. Putnam's Sons, New York. 



Breeder, C. M., Jr., 1929. Field Book of .Marine Fishes of the 

 Atlantic Coast. J. P. Putnam's Sons, New York. 



Clements, W. A. and G. V. Wilby, 1961. Fishes of the Pacific 

 Coast of Canada. 2nd ed. Bull. Fish. Res. Bd. Canada, 

 no. 68. 



Coates, C. W. and J. Atz, 1954. Fishes of the World. In 

 The Animal Kingdom, Vol. 3, bk. 4). Greystone, New 

 York. 



Eddy, S., 1957. How to Know the Freshwater Fishes. VVm. C. 

 Brown Co., Dubuque, Iowa. 



Herald, E. S., 1962. Lwing Fishes of the World. Doubleday 

 & Co., Garden City, N.Y. 



Hubbs, C. L., and K. F. Lagler, 1958. Fishes of the Creat 

 Lakes Region. 2nd ed. Cranbrook Inst. Science, Bloom- 

 field Hills, Mich. 



Innes, W. T., 1956. Fxotu.-ltjuanum Fishes. 19th ed. Innes 

 Publ. Co., Philadelphia. 



