The Outline of Science 



otherwise , there are many ways in which birds are pre-eminent, 

 e.g. in skeleton, musculature, integumentary structures, and 

 respiratory system. The fact is that birds and mammals are on 

 two quite different tacks of evolution, not related to one another, 

 save in having a common ancestry in extinct reptiles. Moreover, 

 there is no reason to believe that the Jurassic Arch&opteryx was 

 the first bird in any sense except that it is the first of which we 

 have anv record. In any case it is safe to say that birds came to 

 their own before mammals did. 



Looking backwards, we may perhaps sum up what is most 

 essential in the Mesozoic era in Professor Schuchert's sentence: 

 "The Mesozoic is the Age of Reptiles, and yet the little mam- 

 mals and the toothed birds are storing up intelligence and 

 strength to replace the reptiles when the cycads and conifers shall 

 give way to the higher flowering plants." 



2 



The Cenozoic or Tertiary Era 



In the Eocene period there was a replacement of the small- 

 brained archaic mammals by big-brained modernised types, and 

 with this must be associated the covering of the earth with a gar- 

 ment of grass and dry pasture. Marshes were replaced by 

 meadows and browsing by grazing mammals. In the spreading 

 meadows an opportunity was also offered for a richer evolution 

 of insects and birds. 



During the Oligocene the elevation of the land continued, 

 the climate became much less moist, and the grazing herds ex- 

 tended their range. 



The Miocene was the mammalian Golden Age and there 

 were crowning examples of what Osborn calls "adaptive radia- 

 tion." That is to say, mammals, like the reptiles before them, 

 conquer every haunt of life. There are flying bats, volplaning 

 parachutists, climbers in trees like sloths and squirrels, quickly 

 moving hoofed mammals, burrowers like the moles, freshwater 



