Re: The Peters Strikes Back (pterosaurs)

["Chris Bennett" <cbennett@bridgeport.edu>]

----- Original Message -----
From: "Jaime Headden" <ja_headden@qilong.8m.com>
To: <dinosaur@usc.edu>
Cc: <ornstn@rogers.com>; <davidrpeters@earthlink.net>;
<jrccea@bellsouth.net>; <darren.naish@port.ac.uk>
Sent: Saturday, October 11, 2003 6:46 PM
Subject: Re: The Peters Strikes Back (pterosaurs)


> .........

>
>  CoG studies favor a quadrupedal stance is more stable and should
>  be more  favorable for the given pterosaurs, including
>  *Nyctosaurus,* and though any pterosaur can assume a stable CoG
>  while standing bipedally, no study has yet to explain a stable CoG
>  that would prevent toppling while walking bipedally in pterodactyloids,
>  where "rhamphorhynchoids" have a stabilising long tail.
>

Most humans seem to be able to stand AND walk bipedally without toppling
even though they lack a stabilizing tail [even I can do it a lot of the
time!].  All it requires is that one keep the center of gravity over the
polygon enclosing the hind feet or temporarily put it in front of that
polygon so as to move the body forward.  Ignoring the question of whether
any pterosaurs actually were habitually bipedal, I would ask whether there
is any reason to think that some pterosaurs could not have been bipedal.
The point I made about Nyctosaurus in my 1997 terrestrial locomotion paper
(JVP 17:104-113) was that the forelimbs were so long that attempting to put
Nyctosaurus in a quadrupedal posture made the trunk and hindlimb almost as
erect as they would have to be in bipedal locomotion AND also put the center
of gravity really close to the polygon enclosing the hind feet.  If the
hindlimb and trunk are that erect and the hindlimb is bearing almost all of
the weight, then why not walk bipedally?


And the Jim Cunningham replied to Jaime's message:

----- Original Message -----
From: "James R. Cunningham" <jrccea@bellsouth.net>
To: <dinosaur@usc.edu>
Sent: Saturday, October 11, 2003 8:08 PM
Subject: Re: The Peters Strikes Back (pterosaurs)


> Jaime Headden wrote:
> > It is most likely that all
> > pterosaurs could assume a fully quadrupedal standing posture on the
substrate, ground or otherwise. The limbs could certainly move
> > while on the substrate, so they could "walk;" but for some reason, it
seems odd to some that walking was not habitual ... even bats
> > will walk if they must, however puny their hindlegs, and no pterosaur
seems to be as badly designed for walking as the loon is,
> > quadrupedal or bipedal.
>
> As you all know, I'm more familiar with Quetz than I am with any other
> pterosaur, and based on the quetz skeleton, it seems fairly obvious to
> me that they could walk quite effectively in quadrupedal mode, and
> perhaps could even lope or canter (I've speculated re loping for some
> time, but haven't made any effort to prove the capability yet).
> However, I have a great deal of difficulty imagining them taking more
> than a few steps bipedally.  I can imagine scenarios where they would
> need to do that, but not any where continuous bipedal walking or running
> would be an advantage, or even possible.
>

It's a shame about Jim's poor imagination.  I can imagine lots of scenarios
in which some pterosaurs could benefit by walking bipedally rather than
quadrupedally.

> > and though any pterosaur can assume a stable CoG while standing
bipedally,
>
> Static or dynamic?  Dynamic I can imagine (for short periods).  Static,
> I can't.  Has anyone done the numbers on it yet?
>

Do the numbers?  You don't need to do any numbers, just use your common
sense!.  Extend the hindlimb and balance the center of gravity over the
polygon enclosing the hind feet.  What is so hard about that?

Chris


S. Christopher Bennett, Ph.D.
Assistant Professor of Basic Sciences
College of Chiropractic
University of Bridgeport
Bridgeport, CT  06601