31 II. S. Lull — Dinosaurian Distribution. 



been recognized among the specimens received, neither could 

 I find any such fossils myself among the debris of the collec- 

 tions, so often a rich repository for new or inconspicuous 

 specimens. This was true, also, of the smaller collections 

 visited, and I was at last forced to admit that here, at least, the 

 Dinosaurs of Russia like the snakes of Ireland, were conspicuous 

 only by their absence. 



'"This opinion was not changed by a visit to the rich geolog- 

 ical collections of Moscow, which I examined with care ; although 

 other fossil vertebrates, including many reptiles, were abun- 

 dantly represented. I was assured, moreover, by various 

 Russian paleontologists, that in other museums of the empire 

 or in the known localities they had seen no dinosaurian 

 remains." 



This evidence can be interpreted again in the light of the 

 fact that Asia is so largely a terra incognita from the paleon- 

 tologist's point of view, or in that of the physical isolation of 

 Angara during the whole dinosaurian epoch. 



VI. Summary of Migrations and Paleogeography. 



The probable center of evolution and course of migration of 

 the Theropoda has already been sketched. Having their 

 origin apparently somewhere in the northern continent of 

 Laurentia, they deployed southward and westward, covering 

 not only the confines of western Europe but extending into 

 G-ondwana, the southern land mass, during Triassic times. 

 New Zealand they never reached and they may have been 

 retarded in their passage to South America until the beginning 

 of the Lower Cretaceous (see fig. 8). The Sauropoda 

 probably had their origin in Europe, migrating early in 

 Jurassic time to the southern as well as to the western continent. 

 Thence in the southern hemisphere both east, south, and west 

 until their range was almost as great as that of their carnivorous 

 allies. Whether the Danian Titanosaur of southern France 

 was a returned migrant or whether suitable conditions caused 

 it to linger long after the death of all of its neighboring allies, 

 like the Steller's sea cow in Behring Sea, I cannot say. The 

 second idea seems the more probable (fig. 9). 



The Orthopoda (fig. 10) present at first sight a much more 

 serious difficulty in their entire absence from the southern 

 hemisphere. It would seem as though we had here a group 

 the center of whose dispersal was North America. They were 

 truly terrestrial types, many of marked cursorial adaptation, 

 which should be as capable of migration as the Theropoda. 

 They were, however, dependent upon a peculiar sort of 

 food which was in turn dependent upon certain climatic 



