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RE: vaulting pterosaur launch, questions



Tim Williams (twilliams_alpha@hotmail.com) wrote:

<I'm sure he wasn't the first, but the 'running take-off' was discussed by 
Speakman (1993).  It's based on the relatively puny pectoral muscle mass of 
_Archaeopteryx_.  The argument runs that having flight muscle mass at or below 
16% of total body mass renders the bird incapable of a stationary take-off.  
_Archaeopteryx_'s is estimated at 9% - so it's well below the cut-off.  Grebes 
are said to have a flight muscle mass below 16%, which is why they require a 
requiring a "taxiing" run in order to become airborne.  Speakman doesn't 
necessarily endorse this line of reasoning; and the grebe example comes from 
Marden (1987).>

  Correct me if I'm wrong. I recent acquired a new computer, but it is not 
possible to access my file collection on *Archaeopteryx,* or I'd have a clearer 
answer to this, but my understanding is that Ruben's 1991 estimate for 9% 
muscle mass is based on the identification of the Munich specimen having an 
ossified sternum. If there was one, it was likely at least three times in area 
per half. In addition, I am not sure what the insertion points on the humerus, 
scapula and coracoid for the pectoral musculature, not neccessarily just _m. 
pectoralis_, have to say when the size of the origin is unknown.

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

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


> 
> 
> > Birds also don't receive
> > much limb excursion from the femur any longer, so
> shortness carries
> > limited cost (stride length is largely unaffected).
> 
> 
> Yes.  The kinetics do change, especially during rapid
> progression - leading to what's been called
> "Groucho running".    :-)
> 
> 
> Refs
> 
> 
> Marden, J. H. (1987).  Maximum lift production during
> take-off in flying animals.  J. Exp. Biol. 130: 235-258.
> 
> Speakman, J.R. (1993).  Flight capabilities in
> _Archaeopteryx_.  Evolution 47: 336-340.
> 
> 
> 
> Cheers
> 
> Tim
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