52 WATER REPTILES OF THE PAST AND PRESENT 



With the opening of the next great era — the Cenozoic or Tertiary 



-the reptiles dwindled away to their present insignificant position, 



while the birds and mammals appeared in great numbers and 



varied forms. The Age of Reptiles was closed and the Age of 



Mammals had begun. 



The history of the reptiles during the Cenozoic is an uneventful 

 one; they ceased their dominion upon land, in the water, and in the 

 air. Their remains are scanty, for the most part, in the rocks of 

 the Tertiary, and such as are known differ only in details from those 

 now living. The land tortoises only, like the mammals of Oligocene 

 and Miocene times, seized the opportunities of open prairies and 

 prospered. A few of the late Mesozoic forms continued a short 

 while into the Eocene. No new groups, perhaps few new families, 

 came into existence during the greater part of this time; it was 

 the age only of land tortoises and the poisonous snakes among 

 reptiles. 



EXTINCT REPTILES OF NORTH AMERICA 



The oldest known fossil reptile of North America, or indeed 

 of the world, is represented by a single specimen, lacking the skull, 

 from black shales of Middle Pennsylvanian age overlying a coal 

 seam at Linton, Ohio. The specimen was originally described as 

 an amphibian, but was later recognized by Professor Cope as a true 

 reptile. It was more fully described by the writer under the name 

 Eosauravus Copei, who agreed with Cope as to its reptilian nature. 

 Until the skull is discovered, however, the precise relationships of 

 the animal must remain doubtful. 



The next later rocks that have yielded reptilian remains are 

 those of Illinois and Texas formerly supposed to be of Permian age. 

 Later evidence, furnished by invertebrates, however, seems to 

 prove that the lowermost of the strata are of uppermost Carbonifer- 

 ous age. The Illinois deposits, so far as known, are of very limited 

 extent, consisting practically of a single bone-bed in black shale in 

 the immediate valley of the Kaskaskia River near Danville. The 

 known fossils from this bone-bed — all isolated bones — are preserved 

 in the museum of the University of Chicago, and include the types 

 of several genera later recognized in the Texas deposits. 



