R. S. Lull — Dinosaurian Distribution. 37 



Why the Sauropoda lingered so long in the southern hemi- 

 sphere after their apparent extinction in the North, is difficult to 

 answer unless it were because of the limitations of food and 

 climate in the North which did not at once prevail in the South. 

 Even though the Trachodontidse gradually assumed aquatic 

 habits, they were too late to be brought into active competition 

 with the Sauropoda in the northern land mass. 



The carnivores being always present doubtless served at 

 first only to limit the plant-feeding forms ; they may, however, 

 have been responsible for the final blotting out of the Sauro- 

 poda when weakened in numbers and by the burden of racial 

 old age. 



I believe that, all things considered, the degree of moisture, 

 whether atmospheric in accelerating or limiting plant growth, 

 or in the form of actual water barriers, was the most potent 

 factor in the origin, evolution, migrations, and final extinction 

 of the dinosaurian race. 



Williston (1909, p. 401) is inclined to think that "there must 

 have been free communication during part or all of the Meso- 

 zoic time between North and South America, proof of which 

 is seen in the dinosaurs, mosasaurs, and crocodiles, some of 

 them being, according to competent observers, identical generic- 

 ally even with North American forms." This may be true of 

 the crocodiles and mosasaurs and yet imply no land bridge 

 over which dinosaurs could pass. True, fragmentary remains 

 from Patagonia have been referred to Allosaurus so character- 

 istic of the American Morrison, but I seriously question the 

 generic identity of any of the dinosaurs with North xlmerican 

 forms. The presence of the earliest recorded remains near 

 Bahia, on the line of march from the East, may be taken at its 

 apparent value. I have found no evidence in favor of a north 

 and south migration in the western hemisphere. 



These studies only serve to verify for the most part the 

 paleogeographical maps of de Lapparent and Schuchert, for 

 in every instance, with the exception of Patagonia and where 

 the dinosaur was found in salt water deposits, the locality fell 

 upon a land area as indicated upon the maps. I would, how- 

 ever, differ from de Lapparent in his inclusion of New Zealand 

 in the Gondwana continent after the beginning of the Trias. 

 The finding of similar dinosaurs on either side of the Mozam- 

 bique Channel during the Cenomanian, after the cleavage of 

 Gondwana Land into an Indo-Madagascar and an Africo- 

 Brazilian mass, has been explained by Deperet (1909, p. 303), 

 who assumes that a temporary closure of the gap occurred. As 

 the Madagascar types are mainly Sauropod, one of which was 

 found associated with Mytilus and Foraminifera, the closure 

 may not have been complete. It is not, however, necessary 



