THE SERPENTLIKE SEA SAURIANS. 



223 



as a " lizardlike bird "; it was no more like a bird than is a bat; it 

 was a birdlike reptile. These suggestions certainly point to the neces- 

 sity of a revision of the text-books and charts in use in class rooms, 

 which in many instances should become obsolete because of per- 

 fected restorations. 



Specialists regard the marine saurians as having existed some 

 millions of years ago. They conclude that these animals had at least a 

 million years of existence in various forms. "While it may be ventur- 



TR\c 



Skull of Platecarpus cobypu^us (Cope). 



ing into the domain of the encyclopaedia to state the causes of these 

 conclusions, a word here may not be out of place. The Cretaceous 

 formation, in which the marine saurians are found, is of chalk, 

 green sands, etc., and ranges in thickness from ten thousand to 

 twenty thousand feet or more. It existed in the last part of the 

 Mesozoic realm. From the thickness and position in geological 

 strata scientists deduce its age and place in Nature. As the remains 

 of marine saurians are found only in the Cretaceous deposits, special- 

 ists speak of them as existing several million years ago. At that time 

 were numerous fishes, birds, reptiles, and plants. 



On previous pages some remarks have been passed in reference 

 to origin and distribution of the sea saurians. It may not be out of 

 place to exploit further the evolution and sequence of other saurians 

 existing before and contemporaneously with the salt-water group. To 

 do so in a brief way presupposes that the reader has some general 

 knowledge of the times in which these remarkable animals existed. 

 The evolution of animal life can only be discussed in general terms, 

 as completer skeletons are needed to determine the whole subject. 



The duration of saurians extended from the Carboniferous period 

 of the Palaeozoic realm through the entire Mesozoic realm which 

 followed. The original saurian, so far as discovery to date shows, was 

 a cotylosaur, found in the coal measures of Ohio by the late Pro- 

 fessor Cope. This ancestor, Isodectes punctulatus (Cope), was eight 



