200 WATER REPTILES OF THE PAST AND PRESENT 



developed organs, so suggestive of a higher and more perfect mode 

 of respiration, are the vestiges of what were once among some 

 reptiles functional structures, or whether they are rudiments of a 

 higher organization, developing independently in these creatures, 

 cannot be positively determined, but it seems very probable that, 

 far back in geological times, some reptiles, especially the pterodactyls 

 and dinosaurs, had their respiratory and circulatory systems more 

 like those of the birds and mammals of today. Unfortunately, 

 however, if such was the case, we may never be able to prove it, 

 although proof would not be impossible; stranger things than 



fossil hearts have been found by 

 paleontologists! 



The stomach, moreover, in 

 the crocodiles is fashioned some- 

 what after that of the birds, 

 with an imperfect division into 

 crop and gizzard. Some croco- 

 diles of today have the habit of 

 swallowing hard pebbles, as do 

 - T> 1 • r j-i •, -I- many birds. There is an old 



Fig. 104. — Pelvis of crocodile: «/, ilium; ■' 



is, ischium; pu, pubis. myth that the crocodile of the 



Nile swallows a pebble on each 

 of its birthdays, thus giving reliable information as to its age by 

 the number found in its gizzard at its death! And this habit has 

 been suggested for some of the most ancient crocodiles, the teleo- 

 saurs, by the recurring presence of siliceous pebbles found with 

 the remains of their skeletons. And we have seen this pebble- 

 swallowing habit was also characteristic of the plesiosaurs, with 

 whose remains "stomach-stones," or gastroliths, as they have been 

 called, 'are often found. 



All of these various characters of the skeleton and fleshy parts 

 are pretty conclusive evidence that the crocodiles, ugly creatures 

 that they are, today enjoy the highest rank among cold-blooded 

 animals. They are perhaps in some respects of not so high a type 

 of reptiles as were some of the extinct reptiles, but that they have 

 survived so long, so many millions of years, is pretty good evidence 

 of endurance, to say the least. 



