AND ITS INHABITANTS 133 



obliteration of the amphibious habitat, seems to have been the 

 most significant. Dinosaurs have been spoken of as associated 

 with peneplanation and the times of their expansive evolution 

 seem to be coincident with periods of degradation rather than 

 with diastrophism, the latter having a restrictive influence. 



Rise of mammals. Perhaps the most remarkable thing 

 which the history of the Mesozoic brings forth is the immense 

 period of evolutionary stagnation on the part of the mammals. 

 They are first actually recorded in the Upper Triassic rocks 

 of three rather remote localities, North Carolina, Germany, 

 and South Africa, and are already differentiated in dietary 

 habits. During the Mesozoic, they develop in numbers and 

 to a certain extent in tooth specialization. They do not, how- 

 ever, increase markedly in size, but are humble folk, so far 

 as our records have revealed them, until the extinction of the 

 dinosaurs has been accomplished. One cannot but associate 

 the idea of mammalian suppression with that of dinosaurian 

 dominance in the relation of cause and effect, unless it shall 

 some day be revealed that the mammals were undergoing a 

 marked evolution beyond the temperature-limited habitat of 

 the reptiles. That the former showed no marked evolutionary 

 advance in the place where the dinosaurs actually occurred is 

 an attested fact, and the significance of the dinosaurian check 

 is no more graphically shown than by two specimens in the 

 Yale Museum. These are both of Morrison age, from what 

 is known is our records as Quarry 9 at Como Bluff, Wyoming, 

 a locality which has produced a number of the rare mammalian 

 specimens. The striking thing, however, is the association of 

 these jaws, especially the type of Diplocynodon Marsh, with 

 the tooth of a carnivorous dinosaur, possibly Allosaurus. The 

 figure here reproduced (Fig. 25) is from a simultaneous 

 photograph of these two specimens, which are therefore on 

 exactly the same scale. The single dinosaurian tooth greatly 

 exceeds not only the tooth of the mammal, but the containing 



