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Re: Synsacrum



>Thank you for your reply, but your answer leaves some of the same questions
>behind.  i.e. : why rigidity, except for bipedal excursions? Flying dragons
>have no more than two sacrals and they are never bipedal. And what muscle
>attachments would require a synsacrum? Longitudinally the epaxials are
>located in that area. It seems reasonable that additional sacralized
>vertebrae would tend to stiffen this area, structurally relieving stresses
>otherwise born by the epaxial muscles (longissimus dorsi, etc.).  Those
>stresses may have their source in bipedalism.

        Yah, I know my answer was somewhat evasive...it's mostly because
I'm not (yet) a functional anatomist of any note, and can't yet acutally
explain many things.  Sorry.

        The gist of my note, though, was that I still don't think that
pterosaurs were bipedal walkers, at least not most of the time.   Yes, I
know that that also leaves the question of the existence of the synsacrum
wide open -- I just don't have an explanation for that.

        The footprint record of pterosaurs, while still scrappy, is
growing.  _Pteraichnus_ prints from many places have come to light, and, to
my mind, don't match the prints of crocodilians nearly as well as they do
pterosaurs.  They are clearly those of a qudruped -- Lockley even has said
that some prints belong to _Pteraichnus_ that are only of the _hand_, with
no footprints associated.  I'm not absolutely sure of _that_, but that's a
whole 'nother ball o' wax...

        Physics and logic don't lend a lot of credence to the bipedal
pterosaur issue, either...at least, not to my satisfaction.  Pterosaur
heads are immense in proportion to the body, and, while very lightly built,
they're still an impediment.  Imagine carrying a huge kite around above
your head -- any disturbance (such as wind) is going to make walking much
more difficult.  I'm also not convinced about the relationship of the femur
to the pelvis (at obtuse angles a la Wellnhofer, or with the rotated pelvis
and subsequent verticalization of the femur, a la Padian), but I haven't
had the opportunity to actually examine many specimens up close, and so
will reserve final judgement on that until I can do so.



Jerry D. Harris
Schuler Museum of Paleontology
Southern Methodist University
jdharris@lust.isem.smu.edu
        (Compuserve:  73132,3372)

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Humorous Quote Is Forthcoming...

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