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Re: pterosaur crest extensions



Jaime A. Headden wrote:
> 
> I think if the body size, head and neck anatomy were considered, the
> presence of a crest would have to be included as a functional mechanic in
> aerodynamics,

I agree.

> but is it essentially aerodynamic, or is this a constraint
> on its anatomy?

I'd say it's probably a constraint.

 *Pteranodon ingens*/*P. longiceps* has developed a large
> long crest which is not exactly very thin and rather triangular in
> section.

I don't see any particular need for a crest to be particularly thin,
unless it has large surface area.

> That of tupuxaurine (made up, I think, by me) pterosaurs
> (*Thalassodromeus*, *Tupuxuara*) are so large it is incredible how the
> sheer thinness could have withstood shear.

Perhaps an effort was made to keep them as unloaded as possible, to help
minimise shear and tensile forces (actually, to minimise horizontal lift
forces that would give the animal problems with yaw control and torque
on the neck)?  But dependent upon the unloading technique, that would
likely make them subject to flutter, with potentially catestrophic
results.

> Species of *Tapejara* have
> large dorsal crests that would almost certainly affected their
> aerodynamics, but I don't see how these would inhibit flight,

What about the erratic yaw forces produced by flow reversals along the
crest?  As you no doubt know, this is a significant problem for Piper
Cherokees, even with their relatively smaller nosewheel fairings and in
some Cherokees it causes erratic yaw darting which can lead to divergent
spiral descents.  Again, perhaps Tapejarids attempted to keep the crests
unloaded during flight, using some presently unknown technique that
would be worthy of further study (to avoid flutter).

> but also I do not see how they would hve neccessarily made it easier.

I can't see how they would make it easier either.  I can sure see how
they would make it tougher.  Which is why I tend to think they may have
been sexual selection signals, perhaps becoming as large as the animal
could get away with (love them trailing prepositions).

> So, did the
> crest enforce a constraint on distance or mode of flight, or does flight
> have any effect on crest size and shape?

Yes.