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Re: Pterorhynchus dewlap

>  I think lionfish sacrifice a lot of speed for the sake of large 
> ornamentsthat create immense drag in their high-viscocity 
> environment. That being said,
> lion-fish are also predators and the spines are both offensive as 
> well as
> defensive in nature, which is how they can afford to also not be 
> exceptionallyfast. The lionfish's quills are the equivalent of the 
> tortoise's shell, in
> other words.

Probably true; lionfish certainly do not swim quickly.  It also helps that 
their fins fold back against the body.  One quick (slightly tangential) note 
about viscosity in swimming: because water is both much more dense and much 
more viscous than air, the Reynolds number range for flying and swimming 
animals is not actually as different as one might expect.  The difference is 
about 15 fold (because it's the ratio of density to viscosity that counts more 
than either one alone for movement in fluids).  That may seem large, but it 
isn't a huge difference for Reynolds number comparisons (though it certainly 

I wonder if anyone has examined vortex wakes in lionfish at varying speeds 
(okay, unrelated, but interesting nonetheless)...
>  I think this is counterintuitive, however, as such animals as 
> most pterosaurs
> don't seem the kind to gently glide around coal reefs in tropical 
> waters, but
> are, it may seem, to be predators on the wing (anurognathids, 
> pteranodontids,nyctopterids, ornithocheirids, azhdarchids, etc.) 
> which require speed and less
> drag than normal to survive.

Well, it depends on what they were predators of.  Efficient gliding, at 
moderate speeds, might be the best way of making a living by skimming for 
surface fish, for example.  In any case, even with the drag-inducing crests, 
there is no obvious indicator that pterosaurs would need to fly slowly.  In 
fact, with their high-aspect ratio wings and excellent lift coefficients, many 
of them probably flew very quickly (being large helps in that arena as well).  
Granted, they might have had less drag and moved more efficiently without the 
crests, but (as I mentioned in my last post, and as Jim also alluded to) the 
L:D ratio was probably good enough to get by.  I would flip the point of view a 
bit and say that pterosaurs were so efficient that they could afford big nifty 
crests, rather than saying the presence of large crests implies low performance.


--Mike H.