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If hydrodynamic drag is the problem...



If hydrodynamic drag is the problem...
... then perhaps pterosaurs only ate flying fish!

on a more serious note: a good paper using good science IMHO, with one possibly 
overlooked factor.

Humphries S, Bonser RHC, Witton MP, Martill DM (2007) Did pterosaurs
feed by skimming? Physical modelling and anatomical evaluation of an
unusual feeding method. PLoS Biol 5(8): e204.
doi:10.1371/journal.pbio.0050204

I haven't scanned all of the replies to this paper, so forgive me if these 
thoughts repeat those of others. I knew nothing of skim feeding prior to this 
paper.

I note the authors describe the skimming of Rhynchops "in areas of calm, 
shallow water." To me that means, no wind. So Rhynchops is responsible for it's 
own airspeed. That also means its relative airspeed is very close to its 
relative water speed. So hydrodynamic drag is indeed a factor.

Given 65 mph of wind, a pilot can set a small airplane down vertically because 
it's the relative airspeed over the wings that's important, not speed relative 
to the runway. Translated to pterosaurs: the relative water speed can be 
drastically reduced by flying into a strong breeze, as is often the case at 
coastlines at various times of the day. As the authors remind us, drag 
increases with speed and decreases with lack thereof. 

The question is: does flying into the wind decrease the list of hydrodynamic 
drag problems to the point that they are no longer problems? 

If so, maybe skimming, dipping, stabbing or whatever can once again continue in 
the traditional fashion.

Just wondering.

David Peters
St. Louis