Re: Pterorhynchus dewlap

[Michael Habib <mhabib5@jhmi.edu>]

> > Ebel's work aside (it's been discussed before on the list, as far as 
> > I recall), I wonder if any pterosaurs could submerge (partially or 
> > completely) for brief periods?
>
> Interesting. I'm sure birds don't have a patent out on water repellent 
> coverings of wings. Not knowing more about the nature of the 
> integument of pterosaur wings (could velvet or waxy coating be ruled 
> out?), I would guess that any lineage of flying animals that have to 
> deal with the aquatic environment over such a long period of 
> geological time could have perfected this, as birds have, which I 
> suspect is a major reason they can dive and then escape the water to 
> launch back into the air.

I suspect that pterosaurs did not have much ability to swim underwater, 
but not because of waterproofing issues.  The hindlimbs of pterosaurs 
are not well constructed for subaqueous foot-propelled paddling (there 
is some possibility of surface swimming, though even that seems 
dubious).  Mostly, the hindlimbs are simply not as robust as would be 
expected for extended paddling.

That leaves the forelimb, and I sincerely doubt that pterosaurs could 
have managed amphibious flight given their wing structure.  First off, 
the wings are far too lengthy (long moment arm), and much to fragile at 
the distal end.  Additionally, the bone stiffness is rather low in the 
distal wing bones (despite maintaining high strength), especially in 
pterodactyloids.  I'm also not certain if pterosaurs could manage a 
power upstroke (I don't just mean an active upstroke, but a fully 
powered one).  In fact, pterosaurs probably used passive upstrokes (as 
part of a continuous vortex gait) most of the time, given their size 
and speed.

Of course, shearwaters (soaring birds related to albatrosses, but much 
smaller) manage amphibious flight with long wings.  However, they have 
thickened bone cortices (compared to non-diving procellariiforms), 
flattened humeri, and they flex the handwing back almost 90 degrees 
(ie. at the wrist) during swimming.  Shearwaters are also not 
particularly large (around 1 kg).

Bats are also not good divers, even those that hunt aquatic prey 
(though some can take off from the surface, albeit with difficulty).  
This is not to draw an serious parallels between pterosaurs and bats 
(which have practically polar opposite flight modes), but to point out 
that for 2/3 groups of flying vertebrates, despite dealing with the 
aquatic environment in some way, subaqueous diving simply never shows 
up.

Cheers,

--Mike H.