AND ITS INHABITANTS 131 



curiously linked together, for although unrelated, their habitat 

 and habits seem to have been very similar and their extinction 

 was apparently simultaneous. What was the physical cause 

 of this extinction, which Is believed to have occurred in the 

 Comanchian, we do not know, for there is little evidence of 

 climatic change. It may have been a temporary restriction 

 of habitat, but curiously enough, these dinosaurs managed to 

 survive the uplift at the close of the Jurassic, but are ap- 

 parently unknown, with a possible exception In Patagonia, 

 after the much less extensive Comanchian movement. 



All of the most impressive characteristics of both Sauro- 

 poda and Stegosauria, huge size, small brain, deficient teeth, 

 and, In the latter, huge upstanding plates and spines, are to 

 the paleontologist indications of the overspecializatlon which 

 he interprets as racial senility. With such forms these char- 

 acteristics, when coupled with a long period of adolescence 

 and the consequent slow breeding which may safely be in- 

 ferred, render their extinction imminent. 



Gadow,^ in speaking of the habits of recent crocodiles, says : 



"In cooler countries they hibernate In the ground; and In hot 

 countries, which are subject to drought, some kinds aestivate 

 in the hardened mud ; or they migrate. When, during a pro- 

 longed drought on the Island of Marajo, at the mouth of the 

 Amazon, the swamps and lakes were dried up, the alligators 

 migrated towards the nearest rivers, and many perished in the 

 attempt. On one farm were found 8,500 dead, and at the end 

 of Lake Arary more than 4,000. Such occurrences in bygone 

 times may perhaps explain the masses of bones found here and 

 there in a fossil state." 



From this it will readily be seen how small a climatic change 

 might account for the serious depletion of an army of huge 

 forms, perhaps never very numerous as to individuals, and 



^ Gadow, H., "Amphibia and Reptiles." Cambridge Natural History, vol. 8, 

 1909, p. 447. 



