CLASS MAMMALIA. MAMMALS 



491 



as that of the highest ape, and in his erect 

 bipedal locomotion. The hairy covering is 

 not well developed, and the great toe is not 

 opposable. The mental development of man 

 has enabled him to accommodate himself 

 to every climate and to dominate all other 

 animals. 



Domesticated mammals 



The most common domesticated mam- 

 mals are the dog, horse, ass, camel, cattle, 

 sheep, llama, goat, pig, rabbit, and cat. Dogs 

 have become changed under domestication, 

 until there are now more than 200 breeds. 

 The immediate ancestors of the horse are 

 not known, but the more remote are well 

 known (see Chap. 36). The ass is descended 

 from the African wild ass, Equus asinus. 

 The Arabian camel is thought to have orig- 

 inated from wild stock in Mongolia. The 

 cattle of Europe and America were prob- 

 ably derived from the aurochs, Bos primi- 

 genius, of Europe. 



Sheep have probably arisen from wild 

 sheep of the genus Ovis. Goats have been 

 domesticated since the earliest times, and 

 their wild relatives are abundant in many 

 parts of the world. Our domesticated pigs 

 are descended from the wild boar, Sus scrofa, 

 of Europe. The remote ancestor of the com- 

 mon house cat was probably the African 

 wildcat Felis libica. 



Fossil mammals 



Many of the orders of mammals are 

 known only from fossil forms. The earliest 

 known remains are of small species. In Cre- 

 taceous times the evolution of the existing 

 orders of placental mammals took place. 

 The Cenozoic Era is called the "Age of 

 Mammals," since this interval of about 60 

 million years between the Mesozoic Era and 

 the present time witnessed the ascendency 

 of mammals and the inauguration of their 

 dominance over all other animals. 



Among the fossil mammals found in 



North America are: (1) the archaic un- 

 gulate, Uintatherium (Fig. 364), which was 

 almost as large as the largest existing ele- 

 phants and possessed three pairs of conspicu- 

 ous protuberances upon the dorsal surface 

 of its head; (2) the enormous tortoise arma- 

 dillo, Glyptodon (Fig. 364), which was al- 

 most 9 feet in length and was provided with 

 an arched shell of immovable bony plates; 

 and (3) the mastodon (Fig. 364) of Europe, 

 Asia, and South Africa, as well as of North 

 America, which resembled our modern ele- 

 phants in size and shape, and of which more 

 than 30 species have been distinguished. 



COMPARATIVE LIFE 

 SPAN OF ANIMALS* 



How long does a certain mammal live is 

 a frequent question and one about which 

 too little is known. Under natural condi- 

 tions animals rarely live their maximum 

 potential age because of high death rates 

 due to disease, predators, and other factors. 

 The most reliable information about the 

 life span of animals comes from zoological 

 parks where accurate records are kept and 

 animals live under conditions that permit 

 them to reach more nearly their maximum 

 age. For example, a mouse, which may live 

 only a few months in the wilds, can survive 

 years in captivity. 



The following examples of extreme old 

 age of animals, from insects to mammals, 

 were chosen from reliable records of zoolog- 

 ical parks and aquaria all over the world. 



* The comparative tables of the life span of ani- 

 mals is reproduced by permission from Iowa Con- 

 servationist, 16:133 (1957) and was prepared by 

 D.H. Thompson and R. Mann. 



