INTRODUCTION. 



The present paper is the fifth* in the series by the author on the verte- 

 brate fauna of the Permo-Carboniferous beds of North America, pubHshed 

 by the Carnegie Institution of Washington, including the volume on the 

 Permo-Carboniferous vertebrates of New Mexico by E. C. Case, and S. W. 

 Williston of the University of Chicago. The object of this work is to 

 stimmarize, as far as possible, the information gained concerning the verte- 

 brate fauna ; the influence of the environment in its history ; its origin, evo- 

 lution and extinction or disappearance from North America; its range over 

 the continent, and its possible migrations. In order to make clear the con- 

 ditions under which the animals lived and developed it has been necessary 

 to introduce a somewhat extended description of the beds in which they 

 occur and to assemble all possible information relative to the character and 

 the source of the sediments, the climatic conditions, and so forth. For the 

 amount of this material and the abundant quotations included the author 

 may perhaps be pardoned, as it has been his effort to include all possible 

 pertinent .evidence in the knowledge that others may draw very different 

 conclusions from the same observations. 



With the exact age of the beds the author has not troubled himself in 

 this publication; the solution of this vexed question must require distinct 

 treatment and the best efforts of men far better qualified than he is at present 

 to evaluate the evidence of invertebrate fossils. Suffice it to say that from 

 the evidence furnished in detail in the body of this paper he is convinced 

 that the stage of evolution of the vertebrates, their stratigraphic position, 

 and the accompanying invertebrates indicate that the beds are of Permo- 

 Carboniferous age, and this conclusion is reached with a full knowledge 

 that the evidence from fossil plants is in favor of the Permian age of the 

 beds. Conflicting evidence of age from plant and animal fossils is no new 

 thing in stratigraphy, and we must wait until a more complete knowledge 

 can reconcile the different interpretations. 



That our knowledge of the fauna is still incomplete is apparent to every 

 one who has paid any attention to the study or exploration of the beds, 

 but it has advanced so far that it is not probable that many entirely new 

 things will be found, and a summary of the known fauna and an account of 



* I. Revision of the Pelycosauria of North America. Carnegie Inst, of Wash., Pub. 55, 1907. 

 2.' Revision of the Cotylosauria of North America. Carnegie Inst, of Wash., Pub. 145, 191 1- 

 3' Revision of the Amphibia and Pisces of North America; with a Description of Permian Insects, 

 by E. H. Sellards; and a Discussion of the Fossil Fishes, by Louis Hussakof. Carnegie Inst, of Wash., 



" ' '1 Pemo-Carboniferous Vertebrates from New Mexico, by E. C. Case, S. W. Williston, and 

 M. G. Mehl. Carnegie Inst, of Wash., Pub. 181, 1913. 



