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re: the bipedal ptero-challenge



Scott Hartman (DinoBoyGraphics@aol.com) wrote:

<but 1) pterosaurs can't move bipedally like dinosaurs because they a)
don't have their center of gravity in the right place for a horizontal
posture,  b) fail to enlarge their illia anteroposteriorly like theropods
do.>

  Pterosaurs have a very long ilium, but this seems to be adapted to the
leg flexors. The leg extensors, however, attested to by the short
posterior "spur" of the postacetabular ala, are much reduced, involving
the caudofemoralis brevis and flexor tibialis externus muscles, whereas
with the dorsal extension of the ilium as seen in many pterosaurs in this
region, the iliofibularis appears to have been given greater leaverage
nearer to the acetabulum than away from it. This reduced the leg
extensors, and would have hampered a bipedal stance somewhat. I'm
underexaggerating. I have little idea what pterosaurs would want with such
a long, narrow preacteabular ala but perhaps for support of muscles,
support ligaments (if frogs and anteaters use their sterna and
occasionally pelvis to support tongue muscles, mayn't pterosaurs use their
ilia to support their long necks and braces to the cantilevers?) and
integument, as well as increase leverage in the leg flexors.

<2) they don't show the adaptatins to upright bipedalism seen in hominids,
especially the double curve in the sacral series.>

  This may not be neccessarily important, for neither do chimpanzees, and
a chimp can be, albeit with much anger on the observer's part, taught to
locomote exclusively bipedally, but the point may be here that any animal
can move bipedally at will, but adaptations to bipedality, which
aforementioned Jesus lizards or the frilled lizards lack, are apparently
lacking. Not pterosaur has enforced the hindlimb and a locomotory organ.
The feet are small, the tibia slender, and the femur retains a long curved
with an elevated neck and small greater trochanter, relative to horizontal
or vertical bipeds, which also increase the diameter of the femur relative
to length and expand the tibial condyles into a planar flexing system that
resists twisting during the stride.

<Of course during take off they'd have to be bipedal for a short period,
and I suspect that the ones that need to run for takeoff did so much like
chinese water dragons (well, with wings of course).>

  The evidence of pterosaurs being bipedal to run into a take off may not
be very well substantiated. Evidence is coming to light that suggests they
may have had moe ... unconventional ... means of lifting off, as any
feature that occludes a bipedal lifestyle may prevent the running takeoff
as well.

  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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