Re: pterosaurs & snakes

[lbowlds@geosociety.org (Larry Bowlds)]

In <9504181653.AA02479@mailhost.ElSegundoCA.ATTGIS.COM> Stan Friesen  
<swf@elsegundoca.attgis.com> writes:
>From: Robert.J.Meyerson@uwrf.edu (Robert J. Meyerson)
> > 
> > As they got rid of their tail, however, the became far less stable in the
> > air.  It was for this reason, that most pterodactyloids have crests on the
> > head; it serves as a rudder while in flight.

>The main evidence *against* this position is the fact that the
>size of the crest is sexually dimorphic in Pteranodon.
>[Male Pteranodons have larger crests than females of the same speces].

>Also, most small pterodactyloids *don't* have a crest (for instance,
>Pterodactylus itself has no crest).

>Thirdly, some of the crests are very small - especially some of the
>nasal crests, as in some of the South American genera.


>I know it may begin to sound like a broken record - but I see
>more evidence for a display function than an aerodynamic one
>for these crests.

>swf@elsegundoca.attgis.com             sarima@netcom.com

>The peace of God be with you.

Isn't it possible that these crests served both purposes? It is easy
to imagine them evolving gradually as sexual display features, and
I agree that this is the most likely source of the crests.

However, why couldn't they also have a functional significance with
regard to flight? In species with a range of crests, couldn't the larger
crest of the male also be related in part to different flight habits,
different foraging behavior, or some other need not required by the
nesting female? And, of course, not all pterodactyloids would have
occupied the same niche, so I wouldn't expect the crests to be the
same in all species, even if crests were essential to some kinds of
flight.

Doesn't the question require that crests be tested for their aerodynamic
effects? If any kind of effect on flight could be demonstrated, wouldn't
that be a strong case for speculating that pterodacyloids used them in
flight?

Larry

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*Larry S. Bowlds        lbowlds@geosociety.org
*Geological Society of America
*Bulletin Managing Editor
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