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RE: pterosaur femora sprawl
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
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.
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