part 1] OF THE UPPER CRETACEOUS IN HUNGARY. 113 



The only groups of reptiles that survived in South-Eastern 

 Europe beyond the end of the Cretaceous Period were the tortoises, 

 which had managed to live on ever since Triassic times, and the 

 true Crocodilia. Even among the tortoises, a diminution is to 

 be found, for the old genera are in part replaced by new ones 

 which appear to have come from Asia. In the Crocodilia, however, 

 it seems as if the new Kainozoic forms were the descendants of 

 the older forms. 



Since the Mesosuchia retreated, as Prof. L. Dollo remarked, at 

 the end of the Cretaceous Period into warmer regions, where they 

 managed to live on into the Eocene (20), the survival of Eusuchia 

 seems at first all the more curious. The reasons for this difference 

 were, however, already in part demonstrated many years ago by 

 Thomas Huxley (34). It is obvious that, for crocodiles who had 

 fed during the Mesozoic Era on sluggish reptiles which could 

 only be torn to pieces or swallowed half alive, in Tertiary times 

 (when they were rather suddenly compelled to live almost ex- 

 clusively on birds and agile mammals) the drowning of the prey 

 became of very great importance. 



There are three reasons why the Eusuchia were not likewise 

 exterminated at the end of the Cretaceous Period, as were the 

 Dinosaurs and the other Ileptilia. First of all, these animals, 

 although living in water, were independent of its vegetation, and 

 did not suffer from the draining of the swamps ; they were, there- 

 fore, better off than the Sauropoda and the Ornithopodidse. 

 Secondly, the different nature of their hunting-grounds prevented 

 them from coming into collision with the Eocene terrestrial carni- 

 vora, as did the Theropoda. Lastly, they suffered less from the 

 change of climate than the Pterosauria ; for, on account of their 

 low body-temperature, they did not feel the loss of heat. It was 

 only at the end of Miocene time, when the European climate 

 became much colder, that the crocodiles were expelled from Europe 

 together with the palm-trees and the remainder of the subtropical 

 vegetation, and driven towards the tropics. 



To sum up, we see how the preservation of a primitive Jurassic 

 land-fauna until the end of the Cretaceous Period was brought 

 about by a geographical factor, and then we see again how the 

 alteration of this factor led, in part directly, in part indirectly, to 

 the nearly total extermination of that fauna. 



VI. Bibliography. 



1. Andrews, C. W. ' On some Bird-Remains from the Upper Cretaceous in 



Transylvania' Geol. Mag. 1913, pp. 193-96. 



2. Do. ' Note on Two New Species of Fossil Tortoises ' Ann. Mag. Nat. Hist. 



ser. 9, vol. v (1920) pp. 145-50. 



3. Arldth, T. ' Handbuch der Paliiogeographie ' Berlin, 1918. 



4. Arthaber, G. von. ' Studien iiber Plugsaurier ' Denkschr. Akad. Wissensch. 



Wien.,. 1919. 



5. Do. ' tjber Entwicklung, Ausbildung & Absterben der Flugsauvier ' Palaont. 



Zeitsclir. vol. iv (1922) pp. 1-47. 



6. B.er, M. ' Beitrag zur Kenntnis der Anatomie & Physiologie der Atern- 



werkzeuge bei Vogeln ' Zeitsclir. f. Wissensch. Zool. 1896. 



Q. J. G. S. No. 313. i 



