climb (monkeys), or swim (whales); but in 

 other species, such as man, the newborn 

 babies must develop even further before they 

 can begin to fend for themselves. 



Unquestionably man and many other pla- 

 centate mammals represent dominant ani- 

 mals in the world of today. There are, to be 

 sure, only about 5000 species, but these are 

 diversely adapted to many sorts of environ- 

 ment (Table 32-2). Moreover, various pla- 

 centates have had tremendous impact upon 

 man's life, starting long before the dawn of 

 civilization, when game mammals provided 

 primitive man with much of his food and 

 clothing. And in civilized times, man's domes- 

 ticated mammals alone have been of incal- 

 culable importance. Without cattle, sheep, 

 dogs, pigs, horses, donkeys, oxen, llamas, yaks, 

 elephants, and so on — as providers of meat, 

 milk, leather, clothes, and endless other 

 things, including just brute strength for the 

 bearing of burdens — the economic basis of 

 modern civilization would have been very 

 much more restricted. 



The Eutheria, or placental mammals, are 



The Animal Kingdom - 675 



widely distributed in nature and they include 

 many species that are very familiar and im- 

 portant. In fact, these animals are so abun- 

 dant and diverse that only the briefest survey 

 of the principal types can be given here 

 (Table 32-2). 



Early in the first epoch of the Tertiary 

 period a number of placental mammals quite 

 different from those of today began to ap- 

 pear. But these archaic placentates did not 

 survive much beyond the epoch. Their place 

 was quickly taken by a rising tide of modern 

 placentates; and by the end of the fourth 

 epoch (Miocene) all our present-day types, 

 plus some others that did not endure, had 

 been evolved. The earliest primate (Table 

 32-2) fossils, apparently, came from lemurlike 

 creatures that lived concurrently with the 

 archaic placentates. However, it was not until 

 the third (Oligocene) epoch of the Tertiary 

 that Anthropoidea began to appear; and it 

 seems fairly certain that no member of the 

 genus Homo appeared until the Pleistocene 

 epoch of the Quaternary period, about half 

 a million years ago. 



Table 32-2— Some Principal Orders of the Eutheria (Placental Mammals) 



