5 8 EVOLUTION IN THE PAST 



Devonian genera had survived : and the outlook was not 

 very promising. In certain localities, however, some fishes- 

 ,of this type measured from five to ten feet in length, and 

 were giants compared with earlier forms (Megalicthys, 

 Rhizodus). Others were more advanced in anatomy. An 

 improvement had been effected in the bony structure of the 

 skull ; and the tail was assuming a modern character. The 

 backbone was still of a gristly substance ; but certain 

 ossifications were going on within the body (Ccdacanthus}. 

 Fishes of this well-equipped family held their own for a long 

 time. 



The fringe-finned ganoids, however, were fast losing 



importance in consequence of the rapid on-coming of their 



ACTINOP- " ray-finned " brethren. These more flexibly finned fishes 



TERYGIAN sparsely represented in the Devonian were now becom- 



GANOIDS ing numerous and varied. Some were long, herring-like 



forms (Palceoniscidcz) ; others had deep and more or less 



compressed bodies (Eurynotus, Cheirodus}. In their case, 



and indeed in the case of nearly all the ganoids, the end 



part of the spinal column was upturned, and extended to the 



extremity of the tail. The tail, therefore, was not of the 



type best adapted for fleet swimming. Improvements in. 



this and other respects were hi store. 



AMPHIBIANS Fishes, progressing though they were, had ceased to be 

 in the van of vertebrate life. A momentous evolution, 

 originating no doubt in much earlier times, was now clearly- 

 revealed by certain vertebrates possessing ability to breathe 

 by lungs, at least in the adult state, and to crawl about on 

 land. Amphibians, in short, had been evolved ; and various 

 creatures resembling in form lizards, newts, and salamanders 

 were now on the scene. 



(STEGOCEPHS) All these pioneers of higher life are known as stegocephs, 

 as their skulls and cheeks were well " roofed " over with 

 continuous bony plates. Very little is known about the 

 early Carboniferous forms ; but towards the close of the 

 Period the animals were in evidence on several lines of evolu- 

 tion. Some, of salamander shape, did not measure more than 

 two or three inches in length. These were triangular-headed, 

 large-eyed little creatures, weak in the limbs, and with 



