MATTHEW, CLIMATE AND EVOLUTION 287 



5) Posterior nares more anterior in position. In the Mesozoic crocodiles, 

 the choanse are situated at the posterior end of the palatines in the long- 

 snouted groups, while in the short-snouted Goniopholidte, they have moved 

 further backward, between the palatines and pterygoids. In the modern 

 Crocodilia, they are still farther backward, entirely enclosed within the ptery- 

 goids. This is an adaptation to lying submerged with the nostrils only pro- 

 jecting above the surface of the water and enables the animal to breathe 

 comfortably in this position. It would naturally develop in the slow, omniv- 

 orous broad-snouted crocodiles and not in the swift-moving fish-catching, long- 

 snouted types ; hence its greater development in Goniopholidae than in teleo- 

 saurs, etc. The fact that it is fully as much developed in gavials as in croco- 

 diles is another reason for deriving both from Goniopholid ancestry. 



According to the above criteria, Alligator is the most progressive mod- 

 ern genus.^^'' Caiman is primitive in (1) ; Osteolcemus in (1) and (2) ; 

 Crocodilus in (3) and to some extent in (4) ; Gavialis and Tomistoma 

 are primitive in (4), divergent in adaptation in other respects, so that 

 comparisons would be miprofitable. We may conclude, therefore, that so 

 far as they go, the Crocodilia accord with the general lines of distribu- 

 tion of other groups. They ranged much farther north during the Ter- 

 tiary than they do now; the most progressive modern genus, Alligator, 

 has the most northerly range, and the jSTeotropical Caiman, the West 

 African Osteolcemus and the cosmopolitan tropical genus Crocodilus are 

 primitive in one or another respect. The gavials also had a wider and 

 more northerly distribution during the Tertiary. 



That the present limits of range are conditioned chiefly by tempera- 

 ture and climate, and that the much wider range in the early Tertiary 

 was due to a warmer climate towards the poles, will hardly be questioned. 

 Of previous limitations and expansions of range in the order, due to 

 previous secular alternations of climate, there is no adequate evidence. 

 The distribution of the more primitive modern genera in widely sepa- 

 rated parts of the tropics; the occurrence of the most progressive genus 

 on the northern borders of the range of the order in tw^o widely separated 

 regions, and, finally, the survival in the Eocene of Patagonia of a croco- 

 dile, Notosuchus, of the Mesozoic type which had disappeared from the 

 Northern world by the Middle Cretaceous, — these facts point to a north- 

 ern rather than a tropical or southern center of dispersal for the order; 

 but the evidence is slight and far from conclusive. 



"0 R. L. Ditmars, of the New York Zoological Park, has observed that crocodiles are 

 decidedly more active and ferocious animals than alligators. I would not interpret this, 

 however, as meaning that they are more progressive, in the sense here used, since the 

 adaptation of the typical Crocodilia is not towards an active life. 



