338 E. C. CASE CLIMATIC ENVIRONMENT OF EXTINCT ANIMALS 



It is natural that the author of this paper should recall instances in 

 point from the remains of animals which dwelt on or near the flats of 

 great streams or lakes, and one clear illustration of what may be learned 

 from a study of the association of forms in the beds occurred in the ex- 

 perience of a recent collecting trip in the Triassic of western Texas. 

 Here an abundance of remains of Phytosaurs and Stegocephalians was 

 found. It is commonly assumed that these animals were at least semi- 

 aquatic in habitat, but every collector is impressed with the fact the re- 

 mains are not found in their natural habitat, and the interpretation of 

 their environment has been uncertain. Last summer such forms were 

 found in beds of hard clay and in beds of clay highly charged with 

 gypsum, but frequently dissociated bones were found in old streams or 

 current channels. In one place a bed of Unios was found associated with 

 water-worn bones, and in such a channel a tooth of the genus Ceratodus 

 was found, the' first reported occurrence of this genus in the Triassic of 

 North America, so far as the author has been able to determine. The 

 climatic habitat of the Dipnoi is well known, and it is not to be doubted 

 that the fossil forms were similar in habits to the surviving members of 

 the group. AVe may, then, be pretty certain that the Phytosaurians and 

 Stegocephalians of this locality lived in a climatic environment not unlike 

 that of western Australia or the region of the Nile. 



So it is that the student of paleogeography must know the physiography 

 of the place and the time, the physiographic changes then at work, the 

 original and altered character of the sediments, and the association of 

 organic forms, and from these he can make an approximate, at least, de- 

 termination of the climatic environment of the forms which he exhumes. 



