CHAPTER VI 



The Evolution of Spiders 



OPIDERS OWE MUCH TO THE PAST. 



The proud jumping spider of today, attired in flowing robes of 

 ermine and crimson and with great smoky eyes intently following 

 every moment of a gleaming bluebottle fly, bears little resemblance 

 to its reserved, myopic forebears. The sedate orb weaver, hanging 

 from a web of wondrous design, has come a long way from the 

 clumsy land creature that first attempted to climb into the shrubs. 

 So changed are many spiders that we can scarcely discern in their 

 bodies any clues pointing to their origin. 



From fossil evidence we know that spiders are ancient creatures, 

 and that they were confirmed land animals before the vertebrates 

 had got free of the bondage of aquatic life. A large part of their 

 evolution must have been undergone during the Devonian Period, 

 which has left one record of an enigmatic spider, Paleocteniza, from 

 the Rhynie Chert of Scotland, occurring with mites and numerous 

 excellently preserved arachnids of the extinct Anthraco?narti. Splen- 

 did fossils come from the coal measures of the Carboniferous Era, in 

 both Europe and the United States, revealing that at that time highly 

 developed, typical spiders were already in existence. Much remains 

 to be learned of earlier araneids, and of the arachnid group that gave 

 rise to them, since we have no evidence to show that spiders have 

 been derived from any other living or extinct group of arachnids. 

 Nor do we have any conclusive evidence that the arachnids evolved 

 from any particular arthropod group. The classical theory of Ray 

 Lancaster, which postulates the trilobites as the ancient group from 

 which have been derived scorpions and typical arachnids on one 

 hand, and eurypterids and king crabs on the other, has been se- 

 verely criticized. More recent evidence, however, strengthens this 

 general thesis and points to the derivation of these diverse arachnid 

 groups from relatives of the conservative trilobites living in the 



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