488 



HISTORICAL GEOLOGY 



was covered with thin scales. The presence of gills in immature 

 specimens shows that they lived in the water at least a portion of their 

 life. 



Certain Permian amphibians (Lysorphus) resembled a modern sala- 

 mander (Amphiuma) in size, shape, and habits so strongly that it 



, , seems actually to have 

 $s been related to it. So 

 abundant are the 

 skeletons of these am- 

 phibians in certain lo- 

 calities in the Permian 

 strata of Texas that 

 hundreds have been 

 found embedded in 

 nodules. 



Amphibians are 

 known from their foot- 

 prints to have lived in 

 theMississippian. The 

 knowledge which can be gained of the animal and of the conditions 

 under which he lived is well illustrated in the footprints preserved 

 in one layer of Mississippian (Mauch Chunk) shale near Pottsville, 

 Pennsylvania. 



Fig. 464. — Branchiosaurus, a 

 phibian of small size occurring 

 "roofed" head, the rings of bone about the eyes, and 

 the scaly covering of the lower side are shown. 



Carboniferous am- 

 abundantly. The 



"There is a succession of six steps, along a surface little over five feet long; each 

 step is a double one, as the hind feet trod nearly in the impressions of the fore feet. 

 The prints were hand-like; that of the fore foot five-fingered and four inches broad; 

 that of the hind foot somewhat smaller and four-fingered. That the Amphibian was 

 therefore large is also evident from the length of the stride, which was thirteen inches, 

 and the breadth between the outer edges of the footprints eight inches. There is 

 also a distinct impression of a tail an inch or more wide. The slab is crossed by a 

 few distinct ripple marks (eight or nine inches apart) which are partiahy obliterated 

 by the tread. The whole surface, including the footprints, is covered throughout 

 with raindrop impressions. 



"We thus learn that in the region about Pottsville a mud flat was left by the re- 

 treating waters, perhaps those of an ebbing tide, covered with ripple marks ; that 

 the ripples were still fresh when a large Amphibian crossed the flat; that a brief shower 

 of rain followed, dotting with its drops the half-dried mud ; that the waters again flowed 

 over the flat, making new deposits of detritus, and so buried the records." (Dana.) 



Origin of Amphibians. — Several lines of evidence show that am- 

 phibians may have been descended from the fringe-finned ganoids 

 (crossopterygians) : (1) the teeth of both are often labyrinthine 





