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Re: evolution of theropod wrist motion



In a message dated 11/19/01 8:46:34 PM EST, jnorton@une.edu writes:

<< If the BCF folks are correct, and theropod dinosaurs are the secondarily 
flightless descendents of early feathered flyers, wouldn't there have been 
enough evolutionary time between the earliest theropods and Deinonychus, for 
example, for theropods to have regained the wrist mobility one would expect 
in a ground-based predator?  Wouldn't the ability to rotate, pronate, 
supinate, adduct and abduct the wrist have been enough of an advantage in 
prey capture to reverse the early flight-stroke adaptations?  Why would the 
limited wrist mobility persist? >>

It ultimately depends on just how useful the return of the grasping functions 
of the forelimb might be to the organisms. There would be little selective 
pressure to reverse the relatively immobile wrists and hands, for example, if 
the animal were already capable (or >incapable<) of using the hands and arms 
with their inherited anatomy. And if the forelimbs performed a better 
brooding function with more winglike wrists, for example, there would even be 
selection >against< re-evolving a grasping function. The chances of the arms 
finding a path through morphological space back to their original 
configuration are in any case pretty slim.