CHAPTER VII 

 CLASS IV. REPTILIA 



It is generally conceded that of all the vertebrate classes the Rep- 

 tilia, past and present, stand foremost in numbers, in size, in range 

 of specialization and in dominance in the organic world. Although 

 the reptiles of the present (crocodiles, turtles, lizards and snakes) 

 play a comparatively unimportant role in the realm of nature, those 

 of the past were frequently of giant proportions and were the dreaded 

 tyrants of the earth, of the waters, and to some extent of the air. The 

 golden age of the reptiles was the Mesozoic, which has therefore been 

 called the " Age of Reptiles. " After a modest career during the early 

 period of the Mesozoic, several specialized groups arose and under- 

 went a remarkable adaptive radiation into all of the principal life 

 zones. Perhaps the most remarkable of these specialized assemblages 

 was that of the dinosaurs, a group that for millions of years held sway 

 over the earth to an extent equaled only by that of Man to-day. Dur- 

 ing this period other orders of reptiles played only a secondary role. 



Dramatic as was this rise to dominance of the greater reptilian 

 orders during the Mesozoic, their sudden extinction at or near the 

 close of this age was even more remarkable. After an unprecedented 

 reign as autocrats of earth and sky and sea for a period of not less than 

 ten millions of years, they abruptly ceased to be. The causes of their 

 extinction are unknown and we can only vaguely conjecture that they 

 died off for no better reason than that they had run their course, had 

 reached the limits of their various lines of specialization, had become 

 stereotyped, senescent, and could evolve no further. To use an idea 

 of Osborn's, they had proceeded to the end of an evolutionary cul-de- 

 sac from which there was no egress. 



Only the crocodiles, turtles, lizards and snakes, among reptiles, 

 were sufficiently generalized to weather the crisis and live on into the 

 Cenozoic age to be the contemporaries of the birds and the mammals, 

 which are the dominant orders of that period. These modern groups 

 have evidently carried on a war of destruction against the reptiles, 

 and still the unequal struggle goes on, with the reptiles on the losing 



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