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re: T&F talks, SVP, Pteraichnus



Generalizations are almost always bad.
Specific matching of prints with printmakers is almost always good. 
When you do match print to printmaker and you find a horizontal backbone, let 
me know. 

Until then, you can see my results for almost a hundred examples at:
ta-dah!

pterosaurinfo.com

David 

-----Original Message-----
From: "Jaime A. Headden" <qilongia@yahoo.com>
Sent: Nov 22, 2004 4:40 PM
To: dinosaur@usc.edu
Cc: davidrpeters@earthlink.net
Subject: re: T&F talks, SVP, Pteraichnus

David Peters (davidrpeters@earthlink.net) wrote:

<I wasn't one of the authors, but I corresponded with "one of the authors"
to produce the animation of the landing pterosaur. "One of the authors"
understands that tracks demonstrate that this genus/clade of pterosaurs
walked flat-footed and quadrupedal.>

  My comments were about general bipedalism versus general quadrupedalism.
The "one" author I was speaking of has published on "his" theory that
pterosaurs are bipedal for the most part, and I asked around SVP for views
on "his" opinions about this NOW, though did not talk to the esteemed
doctor as I could not find him but for a fleeting moment once or twice.
Hence my reticence to name names. The name should be obvious, but I am
holding my tongue still for the sake of not offending or overstating a
position that may have changes.

  The various trackways show that if posture were to be maintained
quadrupedally for most pterosaurs, and the humerus is held horizontally,
then over half the pterosaurs known would be largely horizontally oriented
with respect to the fore-aft direction of the torso. The rather large
lateral tarsals and uneven arrangement of the proximal and distal tarsal
angle, with "higher" or more proximally-positioned lateral metatarsals,
found in some taxa such as *Rhamphothynchus* imply that typical bipedal
walking would have been unconventional and the foot action splayed rather
than parasagittal, given the body's need to disribute weight over each
splayed leg for balance. The leg was splayed, I infer, via the angle of
tibia/femur and at the femoral hip joint, which positions the femur both
slightly more everted laterally and forward of the "typical" restored
position. I am saying this now and can illustrate it at length, without
publication, because the issue for me is not something I really care to
publish on, taking more of my time to study the biomechanics of feeding.

  Extensive trackrecords show a coupled forelimb/hindlimb gait, or at the
least, just a forelimb gait, which is at odds with the bipedal gaint
inferred by others. A quadruped doesn't need the markers for
hindlimb-based walking that a biped does, even should the spine be
vertical (apes are a clear case of this), so there is no real reason a
vertical-sih spine would relate to "essentially" bipedal walking: weight
is still distributed over the forelimbs, and the forelimbs are given a
prominent locomotory function on the ground, belying any exagerrated
exaptation for the role of the legs in locomotion.

  I hope this is clear.

  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.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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