CREATION BY EVOLUTION 



from the Greek work for resplendent. Their arm fins and 

 leg fins were stiff paddles, used more for crawling on the 

 bottom than for propulsion or balancing in swimming. Some 

 that had powerful jaws, such as Dinichthys ("terrible fish") , 

 became /gigantic, having heads three or four feet across and 

 armour in places three or four inches thick. Like our early 

 steam battleships, they specialised in weight of armour, and 

 like these battleships they were soon superseded by rivals 

 which depended for success on swift movement rather than 

 on stolid defence. In a few of the Devonian ganoids the 

 two pairs of paddles were replaced by ordinary flexible 

 fish flns, which were strengthened by fin rays, and in 

 some the paired fins were halfway between these two 

 patterns. 



During the next period (the Carboniferous) ganoids with 

 flexible paired fins predominated, but they were still handi- 

 capped as swimmers by the low degree of hardening of the 

 internal bones, by the incompleteness of the tail as a swim- 

 ming apparatus, and by the unfinished mechanism of the 

 fins along the middle of the body above and below. The 

 tail was formed by the tapering end of the body, turned 

 upward to make an upper iobe; the real fin was below this, 

 as in the sharks and sturgeons of the present day. 



During the Permian and Triassic periods, which followed, 

 the tail in the more progressive fishes lost its upper body 

 lobe by shrinkage and became a most efficient tail fin, and the 

 middle fins were gradually brought up to the most efficient 

 form. The internal skeleton was also gradually hardened. 



Early in the next period (the Jurassic) the backbone in 

 some fishes was completed. Each joint or vertebra was 

 deeply hollowed at each end to admit soft, elastic substance 

 and so to give the great flexibility that is needed for rapid 

 swimming. The bony skull was also completed. At the 



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