400 



PALAEOZOIC SYSTEM OF ROCKS. 



as we approach the time for the appearance of Reptiles, some of these 

 Sauroid fishes seem to become still more reptilian in character, while 

 others become more fish-like. 



Reptiles — Amphibians. — The first known appearance of the class of 

 Reptiles on the earth was in this age : not yet, however, in as great 

 numbers or size, or as high in the scale of organization, as in the next 

 age. The reign of Reptiles had not yet commenced. 



The class of Reptiles may be divided into two sub-classes, viz., True 

 Reptiles and Amphibians. The Amphibians differ so greatly from 

 other Reptiles that they are now usually made a distinct class, inter- 

 mediate between Fishes and True Reptiles. Of these two sub-classes 

 only the Amphibians are certainly known to have been represented in 

 the Carboniferous. Again, Amphibians are subdivided into four or- 

 ders, viz. : 1. Tailless Amphibians (Anoura), such as frogs, toads, etc. ; 

 2. Tailed Amphibians ( Urodela), such as tritons, salamanders, sirens, 

 etc. ; 3. The rare snake-like forms ( Ophiomorpha or Gymnophiona) ; and 

 4. Labyrinthodonts. Of these, only the Labyrinthodonts were repre- 

 sented in the Carboniferous. The other three orders still exist, but 

 the last has been long extinct. The Labyrinthodonts were very large, 

 often gigantic reptiles. They were most of them salamandriform, with 

 long tail, weak limbs, and sluggish movement. Some were pisciform, 

 and had paddles instead of feet. 



We can only briefly describe a few representatives of the class, and 

 draw some conclusions. 



1. Reptilian Footprints. — In the sub-Carboniferous of Pennsylvania, 

 near Pottsville, have been found tracks of a four-footed, crawling ani- 

 mal (Sauropus primcevus), having thick, fleshy feet about four inches 

 long, and making a stride of about thirteen inches. The impression of 



Fig. 577.— Fossil Bain-prints of the Coal Period. 



a dragging tail is also visible. The surface of the slab on which the 

 tracks are found is marked with distinct ripple-bars and rain-prints. 



