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AW: Fwd: Senter 2006, Confuciusornis, and humeral mobility



> >>> The paper makes two assumptions that I
> question:
> >>> 
> >>> 1) the glenoid and scapula  of extinct
> taxa must have the same configuration as in volant
> neornithines in order for the humerus to be raised above the
> dorsum.
> >>> 
> >>> 2) the humerus must be raised to 90 degrees
> above horizontal during the recovery stroke in order for
> flapping flight to be effective.
> >>> 
> >>> I don't see why 1 must be true. There must
> have been transitional phases leading from the anteroventral
> glenoid of lower theropods to the lateral one of birds, and
> very subtle changes, maybe even  just longer ligaments,
> could effect greater mobility in the humerus.
> >>> 
> >>> But I'm especially skeptical of assumption 2,
> not qualitatively but quantitatively. Consider the paper by
> Sokoloff et al. (The function of the supracoracoideus muscle
> during takeoff in the European Starling (Sturnus vulgaris).
> New Perspectives on the origin and early evolution of birds,
> Gauthier, 1999.)
> >>> 
> >>> 
> >>> In their experiments they surgically destroyed
> the supracoracoideus muscles of test subject starlings, then
> filmed them taking off and flying. The starlings' normal
> range of humeral motion during the recovery stroke was 90
> degrees above horizontal. After surgery, this range was
> reduced to just 50 degrees above dorsal. Yet the birds could
> still take off perfectly well from the ground and fly just
> slightly less well than normal.
> >>> 
> >>> Again, modern birds have superlative
> aerodynamic capabilities and highly derived anatomies. They
> also have a wide safety margin built in. In many cases the
> basic functions of powered flight may be possible with far
> less refined equipment.

I never read Senter's conclusions in such absoute terms. To me, he simply 
managed to point out that there was a range of humeral mobility thast had at 
one end fully self-powered taxa (modern birds) and at the other end flightless 
taxa (nonvolant theropods). _Confuciusornis_ (and Archie) are in between. 
Considering their other flight adaptations were also (mostly) less well 
developed, I tend to their being more gravity-powered than self-powered. 

In the case of Archie, a ground-effect glider possibly. _Confuciusornis_ is 
more complicated. Very weird wing shape, only thing that really comes close in 
modern birds are some Apodiformes (Apodidae and some Trochilidae), which 
experience high airflow speeds over their wings.

I would very much like it if someone reanalyzes hindlimb mobility (if it has 
not been done). Possibly the infamous "squirrel pose" has more merit than 
nowadays assumed. _Confuciusornis_ mainly arboricolous, with a basically 
parabola-shaped down-and-up flight path, driven mainly by gravity and 
supplemented (on the upward swing) with wingbeats, would presently be the 
hypothesis I favor. But it's very very tentative.

Still, its wing shape would probably work well under such conditions. Not 
expertly, but there is only so much you can expect in the Early Cretaceous, and 
it might have been the best there was for such a purpose. Perhaps it *was* a 
piscivore and used such a flight path to ambush-predate fish as they came to 
the water surface. The weird bill shape would also tie in well, but this was 
probably not universal among Confuciornithidae. And as a further parallel with 
Apodidae, the short tail. Overall it is very surprising to see such an 
aerodynamic body there and then.

In any case, Apodidae excel at upward/downward flight maneuvers without a 
single wingbeat, and while Hirundinidae are somewhat less capable they are also 
quite good. And they both have this narrow, pointed wing shape with extremely 
elongated primaries and rather short secondaries.

So, as regards fundamental flight capability, confuciusornithids were entirely 
unlike Apodidae. But the similarities in wing shape are striking, and we know 
that in modern birds this wing shape corresponds to high-speed high-g flight 
powered mainly by gravity and conservation of momentum, with wingbeats more for 
acceleration rather than gaining altitude.

Someone whose university has a good design department might see if there is a 
possibility to have a student CAD/CAM a model and study its mobility as a 
thesis project. The _Microraptor_ example 
(http://www.features.ku.edu/microraptors/) suggests that such a project would 
be highly visible (read: "marketable"); the public would love it. And in the 
case of _Confuciusornis_, the hypodigm is so good that it would be a very 
robust study. So it seems like something that very much benefits all involved, 
as well as science, as well as biology as a whole (because the public will be 
reminded in an easily-accessible way why teaching evolution is important). As 
oppsed to the _Microraptor_ project, a _Confuciusornis_ model would need to be 
tested in wind channel, because angle-of-attack and similar things need to be 
investigated.


Regards,

Eike