RE: pterosaur femora sprawl

[Tim Williams <twilliams_alpha@hotmail.com>]

Patrick Norton wrote:


> I think Dial demonstrated rather convincingly several years ago how a
> feathered pre-avian maniraptoran with an incipient "flight stroke"
> capability (selected for whatever reason) could have exploited an arboreal
> environment. 


WAIR (wing assisted incline running) is a nice hypothesis, but it hasn't gone 
unchallenged.  One concern is that this feathered pre-avian maniraptoran might 
not have sufficient musculoskeletal hardware to execute WAIR - especially if a 
rapid upstroke is required.  Young galliforms have the derived pectoral 
architecture of neornithean birds; feathered pre-avian maniraptorans did not.  
That's one of the more salient features of early bird evolution (both pre-avian 
and early avian) - the integument is strikingly similar to that of modern 
birds, but the osteology and musculature took a long time to catch up.  This is 
the essence of the "mosaic" morphology of _Archaeopteryx_ (and relatives).  I 
think WAIR understates this.


> Once in the trees, such an animal would have needed to return
> to the ground somehow, and using whatever aerodynamic function existed in
> their "proto-wings" for that purpose could have been advantageous for a
> number of reasons. 


Can't disagree with that.


> If there was an arboreal stage in the origin of avian
> flight, which is an open question, I don't see a compelling argument for the
> necessity of either a quadrupedal climbing or a four-limb gliding phase.


I agree with the first and last parts of the sentence.  But quadrupedal 
climbing seems at least plausible for _Epidendrosaurus_/_Scansoriopteryx_, and 
maybe _Yixianosaurus_ too.


Cheers

Tim
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