[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Senter 2006, Confuciusornis, and humeral mobility



Figure 39 of Chiappe et al. 1999 shows the well - developed trochleae and
flexor pits on the second digit of GMV-2132. This would seem, to me, to
indicate an ability to flex.



>
> 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/
>>
>>
>


Jason Brougham
Senior Principal Preparator
Department of Exhibition
American Museum of Natural History
81st Street at Central Park West
212 496 3544
jaseb@amnh.org