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RE: Senter 2006, Confuciusornis, and humeral mobility



Jason Brougham wrote:

<That brings to mind one more big difference between Confuciusornis and any 
modern bird. The primaries are distributed along a second finger which is 
robust and retains mobile joints. Unlike any living bird, therefore, the distal 
primaries can be folded relative to the proximal ones. Wouldn't flexion of the 
wing finger, folding the primaries up before the upstroke begins, help reduce 
negative lift?>

  I do not think that this is the case. The wing finger, unlike other 
non-ornithuromorphan theropods, is incredibly modified and appears to lack 
extensor pits on the dorsal margins of the phalanges. The basal phalanx 
(mdII-1) is very broad, while the second phalanx (mdII-2) is narrow and 
attenuated, and the claw almost descriptively "vestigial." I do not think the 
finger was mobile at all, and unlike the condition in *Archaeopteryx 
lithographica*.

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)





----------------------------------------
> Date: Wed, 23 Mar 2011 19:00:33 -0400
> From: jaseb@amnh.org
> To: MHabib@Chatham.edu
> CC: jaseb@amnh.org; tijawi@gmail.com; dinosaur@usc.edu
> Subject: Re: Senter 2006, Confuciusornis, and humeral mobility
>
> >1) the recovery stroke is limited such
> > that it is difficult to get the wing out of circulation in time to avoid a
> > negative lift coefficient and
>
> That brings to mind one more big difference between Confuciusornis and any
> modern bird. The primaries are distributed along a second finger which is
> robust and retains mobile joints. Unlike any living bird, therefore, the
> distal primaries can be folded relative to the proximal ones. Wouldn't
> flexion of the wing finger, folding the primaries up before the upstroke
> begins, help reduce negative lift? It does in bats, right? And wouldn't
> such a snap of the wing finger at some point on the power stroke,
> accelerating the distal primaries to very high speeds, significantly
> increase lift?
>
> >2) there is insufficient excursion on the
> > shortened downstroke to build up to full circulation by the midpoint in
> > the stroke where the primary force production occurs.
>
> Can you say this with confidence without doing any calculations or
> modeling at all? I fear we may be in danger of making a priori qualitative
> assumptions when the answer may be quantitative. In other words, an animal
> with limited dorsal mobility of the humerus may have LESS ability to
> generate lift than, say, a pigeon, but it may still have ENOUGH lift for
> powered flight.
>
> Picture how many different flight strokes could be possible if you add two
> points of wing flexion - at the first and second finger joints. The
> resulting complexity seems daunting to me, at least. I have read that
> bats, which can do this, often fly with different configurations of the
> left and right hand during each wingbeat:
>
> http://blogs.discovermagazine.com/loom/2009/03/19/how-to-be-a-bat-life-in-motion/
>
>