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RE: The Men Who Stare At New Papers



Michael Erickson <tehdinomahn@live.com> wrote:


> But there are facts that support the 2F hypothesis that
> have yet to be addressed by those who reject the hypothesis. For 
> example, I have not heard anyone explain the posterolateral flange on 
> the first phalanx of digit II and strongly bowed metacarpal III in
> _Sinornithosaurus_. These are adaptations for flight. 


But did these "adaptations to flight" begin this way?  In other words, could 
these features have originally evolved for some function unrelated to powered 
flight?


In the evolution of flight in theropods, the key word is "exaptation".  Many 
flight-related features that we see in birds likely evolved originally for 
other purposes, such as the furcula ("wishbone"), long forelimbs, pneumatic 
bones, enlarged breastbone (sternum), and of course feathers.  All these 
features came to be incorporated into the avian flight apparatus (probably in a 
stepwise fashion), but they probably didn't begin that way.


In light of this, the two characters you mention (posterolateral flange on the 
first phalanx of digit II; strongly bowed metacarpal III) might similarly have 
first evolved for a non-flight-related purpose.  For example, are these 
features perhaps correlated with reinforcing feather attachment?  It was once 
assumed that the presence of quill nodes along the ulna was an exclusively 
flight-related character - until they turned up in _Velociraptor_.


Cheers

Tim