132 ANIMALS OF THE PAST 



Silhouettes of those marine reptiles, the Ich- 

 thyosaurs, have been found, probably made by 

 the slow carbonization of animal matter, show- 

 ing not only the form of the body and tail, but 

 revealing the existence of an unsuspected back 

 fin. And yet these animals were apparently 

 clad in a skin as thin and smooth as that of a 

 whale. Impressions of feathers were known 

 long before the discovery of Arch^eopteryx ; a 

 few have been found in the Green River and 

 Florissant shales of Wyoming, and a Hesper- 

 ornis in the collection of the State University 

 of Kansas shows traces of the existence of 

 long, soft feathers on the legs and very clear 

 imprints of the scales and reticulated skin that 

 covered the tarsus. From the Chalk of Kan- 

 sas, too, came the example of Tylosaur, show- 

 ing that the back of this animal was decorated 

 with the crest shown in JNIr. Knight's restora- 

 tion, one not unlike that of the modern iguana. 

 From the Laramie sandstone of INIontana INIr. 

 Hatcher and Mr. Butler have obtained the im- 

 pressions of portions of the skin of the great 

 Dinosaur, Thespesius, which show that the 

 covering of this animal consisted largely, if not 



