MAMMALIA 339 



lying well-watered woodland with ever alert furry forms taking 

 such refuge as the trees and shrubbery or occasional hiding holes 

 could offer, in the midst of stalking terrors such as the world 

 never saw before or since. That the mammals managed to maintain 

 themselves is not surprising, for there is a teeming horde of small 

 mammalian folk in the tiger-haunted jungles of India to-day; and 

 that they did not dispute with the dinosaurs the realms of greater 

 opportunity is but a logical assumption." 



In conclusion it may be said of the Mesozoic mammals that they 

 made less headway in the Mesozoic than did the reptiles in the 

 Palaeozoic; for they were all quite generahzed in structure and of 

 small size. There is evidence that the first mammals arose very 

 soon after the reptiles became well established in the Permian. If 

 this is so, we see that all of the vertebrate classes except the birds 

 had their origin in Palaeozoic times. 



Cenozoic Mammals 



The Cenozoic has been called the Age of Mammals, just as the 

 Mesozoic is called the Age of Reptiles. The same great climatic or 

 geological conditions that are assumed to have led to the extinction 

 of the exuberant reptilian dynasties that flourished during the Meso- 

 zoic may be also given the credit for affording the manmaals their 

 first opportunity to "secure for themselves a place in the sun." 

 After a lurking life in the shades and shadows they were able to 

 emerge into the open and to invade the vast fields of opportunity 

 vacated by the fallen races of reptiles. The small, warm-blooded 

 manamaUan races repeopled the wastes, gaining the upper hand over 

 the few reptihan groups that remained, such as the lizards, snakes 

 and turtles; these in turn took up the furtive life that the mammals 

 left behind. The mammals had been under pressure during the en- 

 tire Mesozoic, and when the pressure was removed they expanded 

 marvelously. 



The Archaic Mammals of the Cenozoic. — The mammals of the 

 early periods of mammalian deployment during the Tertiary are 

 usually called archaic manmials. They differ from modern mammals 

 in the following particulars: 1, Their feet were conservative, showing 

 little advance upon reptilian conditions; 2, their molar teeth were 

 very little differentiated for the various feeding habits; 3, the brain, 

 especially the part which is the main seat of intelligence (the cere- 



