^ 



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k- 





to 



9 





*t 



% 



e. 



\ 



a 



Low 



batra- 

 'ra of 



J, and 



irmost 

 ilk, as 



!' 



e 



nif 

 ?eter> 



o-enus 



Lous of 



arenew 



'pen. 

 ad f 



• con. 



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larger I 









rtoi 

 • re 







ral 



A 



are 



tiofl 



ff 







1 

 f 





5 





Ch. XI.] 



EXTINCT ORDERS INDICATE TEMPERATURE. 



215 



table of the distribution of reptiles in past geological ages * 

 that of the five living orders, crocodiles, lizards, tortoises, 

 a kes and frogs, the two last mentioned do not extend 

 into the Secondary or Mesozoic periods, but the three first, 

 the Crocodilia, Lacertia, and Chelonia, are met with in full 

 strength in Cretaceous times, where they become associated 

 with no less than three extinct orders, namely, Pterodactyls, 

 Ichthyosaurs, and Plesiosaurs. Respecting the first of these, 



some 



namely, the flying reptiles, it has been argued, with 

 show of reason, that we have no right to assume that 



highly 



are so 



But the same argument will 



s 



they require! a hot climate, because they 



organised, and have so near an affinity to birds in structure, 



that they may have been warm-blooded, and as capable as 



birds of sustaining great cold. 



not apply to ichthyosaurs or to plesiosaurs, nor to the 



numerous chelonians which occur in the different division 



of the Cretaceous period, including the Wealden strata, in 



which large terrestrial saurians are so conspicuous. 



How far extinct orders c 

 It has been objected, that in speculating on the habits and 

 physiological constitution of plants and animals of an epoch 

 so distant from our own as the Cretaceous, we enter a 

 region of doubt and uncertainty, because even the eocen 

 species are distinct from the living ones, while the creta- 

 ceous fossils differ as much from the eocene as do the latter 

 from living types. Dr. Fleming, therefore, when engaged in 

 a controversy with Dean Conybeare, in 1830, as to the proofs 



e 



of a hotter climate 



the olden time, declared that the 



reasoning of his opponents was illogical, and their mode of 

 dealing with the subject unfair. ' They were playing,' he 

 said, 'with loaded dice;' for the larger number of genera 

 are now in tropical and sub-tropical zones, not because they 

 could not live in colder regions, but simply because the land 

 and sea in those zones is of wider extent, and supports in equal 

 areas a greater exuberance and variety of animal and vegetable 

 forms. According, therefore, to the doctrine of chances, the 

 majority of the genera of any past epoch, whether they be 



* Owen, Paleontology, p. 321. 



