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POPULAR SCIENCE MONTHLY 



discovery that Naosaurus was an 

 eater of molluscs and not a preda- 

 tory form makes more perplexing 

 than ever the question as to the 

 use of the spines on the hack. On 

 such a thick-bodied, sluggish mud- 

 o-ruhher, the cross-barred spines 

 must have had about the same 

 value as an ornamental frieze on a 

 canal boat. What conditions of 

 environment could have produced 

 similar structures on creatures of 

 such dissimilar habits as Dime- 

 trodon and Naosaurus? It is as 

 if the tiger and the badger should 

 meet on common ground and de- 

 velop highly specialized, unwieldy 

 and seemingly useless structures 

 of close similarity. 



Of what use were the spines on 

 the backs of these animals? The 

 structure shows that they were not 

 covered with flesh, but were united 



a thin membrane through 



hv 



Fig. 5. Portion of the Vertebral 

 Column of Dimctrodon, showing tin- 

 enormous development of the spines. 



which the spines showed as plain- 

 ly as the fin rays in the fin of a fish. 

 It is hard to conceive of this great 



Fig. 6. Restoration of Dimctrodon. 



