MESOZOIC ERA: THE AGE OF REPTILES 



563 



jaw would insure the retention of every fish captured, but would 

 prove a hindrance to its being swallowed quickly. Possibly 

 toothed birds and pterosaurs were obliged to go to land before being 

 able to devour their food, 

 but those with horny beaks 

 could bolt their food on the 



wing. 



Fossil birds are compara- 

 tively rare, even from the 

 rocks of periods when birds 

 were abundant, because of 

 the lightness of the skele- 

 tons, which caused the car- 

 casses to float on the seas 

 for a long time before sink- 

 ing to the bottom, with the 

 result that the skeletons 

 were usually devoured by 

 fish or beasts of prey before 

 they had a chance to be 

 buried in the sediments. 

 Bird fossils are rare in the 

 Mesozoic also since they are 

 not now and were not then to J IG - 5*3- — Ichthyosis, a small, toothed bird 

 . „ with strong powers of flight (Cretaceous). (After 



any extent swamp dwellers, Marsh.) 



and what is known of Meso- 

 zoic land life is chiefly limited to the fauna of the swamps. Because 

 of this, it is probable that only a small part of the bird life of the Cre- 

 taceous is known. 



REFERENCES FOR BIRDS 



Hutchinson, H. N., — Extinct Monsters and Creatures of Other Days, pp. 211-220. 



Lucas, F. A., — Animals of the Past, pp. 70-89. 



Marsh, O. C, — Birds with Teeth: Third Ann. Rept., U. S. Geol. Surv., 188, 



pp. 45-88. 

 Newton, — A Dictionary of Birds. 

 Woodward, A. S., — Vertebrate Paleontology. 

 Zittel-Eastman, — Textbook of Paleontology. 



Mammals 



A few very small lower jaws have been discovered in Triassic 

 deposits of America and Europe (Dromatherium, Fig. 524), which 



