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Re: Senter 2006, Confuciusornis, and humeral mobility



And what about non - glenoid means of raising the primary tips above the 
horizontal? Rotation of the humerus around its long axis, which happens in 
living birds, can alone raise the manus above horizontal. Extension of the 
manus could increase this effect, and the effect would increase with longer 
primary lengths, in that the primary tips would be that much farther above 
horizontal.

Your conclusions below seem to suggest that most of the upward and forward 
force produced from a  flap comes from the recovery stroke, but surely it must 
really be the power stroke.

Ventral clapping may not produce aerodynamic forces like a neornithine, but the 
forces may well be appropriate for propulsion. 

 If a starling can take off with a  power stroke that starts at 50 degrees 
above horizontal and then continues down a further 90 degrees to the midline 
then, knowing nothing else,  it seems that only a minority of lift, something 
like one third, is generated above the horizontal.

-Jason

On Mar 23, 2011, at 2:19 PM, Habib, Michael wrote:

> It's an interesting idea, but generally speaking, the half-stroke ventral 
> clapping kinematic you're suggesting would not produce appropriate 
> aerodynamic forces.  Without getting into at length, the upshot is that the 
> animal will produce about as much force counter to the direction it needs as 
> it will useful aerodynamic force (i.e. it will go down and back about as much 
> as it goes up and forward).  It is an interesting thought, though - it gave 
> me pause for a moment.
> 
> Cheers,
> 
> --Mike H.
> 
> 
> On Mar 22, 2011, at 10:39 PM, Jason Brougham wrote:
> 
>> On the subject of humeral mobility and powered flight, is it possible that
>> the first stages of flapping could involve flapping the wings downwards
>> only?
>> 
>> In other words, on the lineage leading from a glider to a powered flier,
>> could the early stages involve gaining lift and extending glides by
>> flapping the arms from horizontal ventrally down to meet at the midline?
>> 
>> Then, in later stages of refinement, the recovery stroke could be added by
>> more complex shoulder modifications?
>> 
> 
> Michael Habib
> Assistant Professor of Biology
> Chatham University
> Woodland Road, Pittsburgh PA  15232
> Buhl Hall, Room 226A
> mhabib@chatham.edu
> (443) 280-0181
> 

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544