No. 586] 



THE COAL MEASURES AMP HI HI A 



external form. Many of the representatives of the Am- 

 phibia in the Coal Measures of North America are highly 

 specialized and adapted for a variety of modes of life. 

 One of the most significant factors in the derivation of the 

 early land vertebrates from the fishes is the question of 

 the origin of limbs from fins, on which much has been 

 written from a theoretical standpoint, but nothing has 

 been seen in the nature of material supporting and defin- 

 ing the details in the process of evolution. It must be 

 remembered, however, that the Coal Measure forms are 

 Amphibia in a high stage of development and when new 

 discoveries show us the anatomy of the forms from the 

 Mississippian, Devonian and possibly the Silurian, then 

 we shall be in better shape to discuss the question of the 

 origin of tetra- and pentadactyl limbs. 



The evolutional status of the Coal Measures Amphibia 

 may be briefly stated. They were an assemblage of 

 forms, highly developed and highly specialized, with few 

 primitive characters which would tend to ally them di- 

 rectly with any known group of more primitive verte- 

 brates. We should expect to find among these Paleozoic 

 Amphibia some evidence of a transitional type of limb 

 (11) structure between that of Eusthenopteron (12), or 

 allied Crossopterygian, on the one hand, and the penta- 

 dactyl terrestrial vertebrate, on the other. But such evi- 

 dence is not forthcoming among the material at present 

 available. Evolutional forces had brought about a wide 

 diversion of faunas in the Coal Measures, so that the spe- 

 cies are easily separable into distinct geographic groups, 

 which are more distinct than are the species of Amphibia 

 inhabiting the same regions to-day. 



The living Amphibia are much more commonly iden- 

 tical in eastern Ohio and northern Illinois than were the 

 species of the same order during the Coal Measures. 

 Species of Nccturus, A)nbli/stonia, liana and Bufo are not 

 widely different in the two localities referred to ; yet the 

 species of Amphibia during the Coal Measures at Maxon 

 Creek, Illinois, and Linton, Ohio, are widely distinct. 

 They are, in fact, more widely distinct than the species of 



