112 BARON P. NOPCSA ON THE PRIMITIVE REPIILIA [vol. lxxix, 



feel it indirectly, so long as the change is not very violent or 

 abrupt. Thus, even those feeding on a certain flora may linger on 

 for a while after its extinction. 



As to the Ornithocheiridae, it was, I believe, not so much 

 the rivalry of the birds that led to their extinction (for birds and 

 Pterosauria occur together from Jurassic times onwards), but the 

 change in climate. The Pterosaurians are the only reptiles (for 

 reptiles we must call them) in which we have to presume, despite 

 Arthaber's arguments (5), that the body-temperature was high, 

 although they had no heat-preserving integument. 



Already in the Crocodilia (which belong to the Archgeosauria, 

 and therefore are closely allied to the Pterosauria) the separation 

 of the heart-chambers indicates a comparatively advanced stage 

 (12, 26). They present, besides, several structures that prevent 

 as long as possible an influx of blood poor in oxygen into the 

 brain (12) ; this shows how sensitive is the brain in that respect. 



In Pterosaurians the brain is much more developed than in 

 crocodiles ; besides, it shows a marked increase of size in the course 

 of evolution, being larger in the Ornithocheiridse than in Parapsi- 

 ceplialus (4), and we may quite safely infer that in these animals 

 it was at least as sensitive to carbon dioxide as in crocodiles. This 

 supports the argument, as H. Gr. Seeley pointed out, for a heart 

 with separated chambers, whereby the body-temperature would be 

 raised. Where in human pathological cases the heart-chambers 

 communicate, the body-temperature attains only 32° C. (77). 



Not only the circulatory, but also the respiratory, organs of 

 Pterosaurians indicate that the body-temperature was conxparatively 

 high. In these agile reptiles the air-sacs were not developed 

 according to the usual reptilian type, but extended even into the 

 bones. In birds the air-sacs serve, as proved again by Bser (6), to 

 augment in every possible manner the contact of fresh air with the 

 rapidly circulating blood. In the lightly-built primitive Dino- 

 saurs (62) and Pterosaurians their function was probably the 

 same. In lizards the heart beats 10 to 200 times, in birds 300 to 

 1000 times, in a minute. This second argument corroborates, so 

 far as Pterosaurians are concerned, the conclusions arrived at by 

 means of the first. As for Dinosaurs, I do not believe that they 

 were warm-blooded, for, in the course of their evolution, the brain 

 degenerates (62). 



While all mammals and the warm-blooded birds have a heat- 

 preserving integument, the Pterosauria had none. The} r must, 

 therefore, with a falling temperature have suffered more from cold 

 than mammals or birds ; and, since the change of the flora at the 

 end of the Cretaceous Period indicates a cooling of the climate, 

 perhaps we may have here a clue to their disappearance (25, 35). 



The coincidence of the extinction of Pterosauria in America with 

 the appearance of the Kainozoic flora (11) is a most extraordinary 

 feature, for no direct connexion seems to exist between fish-eating 

 Pteranodontidse and plants. This indicates the direct influence of 

 the climate. 



