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Re: pterosaur wings and scans



David Marjanovic and Jim Cunningham respond to comments made by David
Peters on *Nyctosaurus* locomotion, including the data concerning the
enormously long antebrachium and epibrachium of the animal versus other
animals, precluding an obligate bipedal posture. Here's my take on the
issue, as I'm having a good time and my opinion streak is running. This is
just my assessment.

  It is not absurd that *Nyctosaurus* or other long-armed pterosaurs with
short legs like *Arthurdactylus* could move quadrupedally, and data from
Unwin with computer models using the former taxon have shown that, if even
cumbersome, it could walk quadrupedally, same as how loons, if neccessary,
can and will walk. As Jeff Goldblum said in one well-known movie, "Nature
will find a way." Other models using different pterosaurs also show that a
pterosaur on its hindlimbs would have to be nearly vertical in orientation
to walk with its CG situated above the hips, in order to properly balance.
At this point, it is so ungainly that it is just not likely; meanwhile,
further unpublished but presented models indicate the quadrupedal stance
and phases of step is the only model that supports the CG balanced between
all four legs. Other animals that walk bipedally have adapted their limbs
and spine to accomodate the CG either between the knees or above the hips,
as in birds and humans, and gorillas are a perfect example of a faculative
quadruped that can switch to bipedal in some cases, but locomotes
quadrupedally for nearly all of its travel time. Some apes have arms so
long it makes quadrupedal locomotion extraordinarily difficult, if nigh
impossible, but even orangutans will use their arms. But that's a caution
on the *Nyctosaurus* quadrupedal model, too, save for the fact that the
hips, spine and legs of these particular apes are arranged differently for
brachiating arboreal locomotion (vertical spine, ilia deflected laterally,
femora nearly vertical without much lateral splay, large calcaneal heels
for plantigrade stance) not seen in any pterosaur; the hips of pterosaurs,
in fact, preclude vertical stance without flexion of the knees, and unless
this animal walked with a slow, ungainly crouch or squat, I see no logical
reason such a system should be advocated for pterosaurs of any stripe.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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