MATTHEW, CLIMATE AND EVOLUTION 277 



of footprints of the Connecticut Valley sandstones shows that there must 

 have been also a great number and variety of small bipedal three-toed 

 forms all presumably dinosaurs, and other reptiles with shorter feet and 

 more numerous toes which may also have been dinosaurs, although not 

 generally so referred. LulP^ states in regard to the latter : "These forms 

 seem to represent survivors of the ancient stem from which the dinosaurs 

 arose; they may, however, represent primitive quadrupedal dinosaurs 

 which had not yet acquired the erect gait." He calls attention to their 

 possible relationship to Protorosaurus and Kadaliosaurus. 



From these and other fragments of evidence, Ave may reconstruct a 

 concept of the dinosaurs as a land adaptation developed during the arid 

 Permo-Triassic climatic phase, corresponding to the later deployments of 

 the mammals along the same lines of adaptation and under a similar 

 impelling cause of progressive aridity and continental expansion. Dur- 

 ing the base-leveling and submergence and moist tropical climate of the 

 Jura, these dry-land adaptations reinvaded the swamps and coast- 

 marshes, the least specialized types (cf. Protorosaurus), more quad- 

 rupedal and some of them long-necked, reverting farthest towards an 

 aquatic life and specializing into the peculiar Sauropoda, while the higher 

 bipedal types retained more of their terrestrial habitat but evolved into 

 huge, massive armored and bizarre creatures, to be paralleled in habit 

 and type at a later date by the bizarre specializations of the Eocene Mam- 

 malia. These are the familiar dinosaur fauna of the Upper Jura and 

 basal Cretaceous. The drier uplands of that time must have been ten- 

 anted by lighter, smaller dinosaurs, but of these, in my opinion, we have 

 little direct evidence. But that they continued to exist and cari-y for- 

 ward their primary lines of adaptation is shown by the subsequent history 

 of the order.^**" 



In the Lower Cretaceous occurred a swing towards emergence and arid 

 conditions, not extreme, but sufficient to wipe out the sauropod dinosaurs 

 in the northern world. They survived, however, in the southern conti- 

 nents until, in the middle and later Cretaceous, the pendulum swung back 

 to a marked extreme of submergence and moist-tropical climate, and 

 their remains are found in late Cretaceous beds in South America, East 

 Africa, Madagascar and Australia. The correlation of these beds is in 

 need of revision, however; they may be Comanchean. In the Northern 



»» R. S. Lull : I. c, p. 482. 1904. 



1™ R. S. Lull ("Dinosaurian Distribution," Amer. .Tour. Sci., vol. xxlx, pp. 1-39, 1910) 

 has admirably summed up the data regarding the geological occurrence of dinosaurs. 

 While not agreeing in all respects with his Interpretation, I take pleasure in noting the 

 accuracy and clear presentation of the evidence as worthy of the high regard in which 

 Its author is held by his confreres. 



