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Re: Science feather strength debate



Erik Boehm <erikboehm07@yahoo.com> wrote:


> Define "complete", not having the same stroke as modern birds, doesn't mean 
> they didn't have a functional flight stroke.


I know.  Not even N&D argue that _Archaeopteryx_ and _Confuciusornis_
were incapable of a rudimentary flight stroke.  In their words (Nudds
and Dyke, 2010):

         Because even rudimentary forelimb movements can generate
useful thrust... some
         thrust generation by these fossil birds cannot be discounted,
but the vigorous flapping
         flight of modern birds is highly unlikely.


Senter seems to be more conservative, arguing that flapping was
precluded by the inability to execute the recovery phase of the
stroke, due to the orientation of the shoulder joint


> Any keel at all would suggest some form of flapping to me.
> If it is an attachment area for muscles for the wing... my imagination is 
> insufficient to imagine what those muscles were used for if not flapping.


_Mononykus_ has a keel.


Now, I'm not in any way suggesting that basal birds used their
forelimbs in the same way as alvarezsaurs (!)  I'm merely pointing out
that the presence of a keel does not necessarily correlate with a
flight stroke.  It's possible that the development of a keel in birds
preceded the advent of powered flight, as did the evolution of the
furcula, feathers, and elongated forelimbs.


> I think it is too big of a leap to go from: obligate glider -> must climb 
> trees. I also don't think it is correct to assume elevation was needed.
> At many coastal areas, gliders can launch from more or less flat ground, from 
> about a meter or two above sea level, and start soaring.


I'm guessing that your "gliders" are actually powered fliers that
happen to glide as a prelude to soaring.  So they aren't really
gliders.  Ergo, it's perhaps not appropriate to use these soarers as
templates for incipient flight behaviors, because their flight
apparatus is so much more advanced than what was present in basal
birds.


>  All I've heard is that archy was from an area that used to be islands.


True.  So it is tempting to think that _Archaeopteryx_ could use
flight to commute between islands.  That doesn't mean this is what
happened though.


Cheers

Tim