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Re: _Scipionyx_ and diaphragms again



Aren't all these points pointing to a Mesozoic
atmospheric oxygen count of some 30%-35%, more than
twice the oxygen content that has been recorded in a
major present-day city(12%-15%)?
--- David Marjanovic <david.marjanovic@gmx.at> wrote:
> 
> ----- Original Message -----
> From: <archosaur@usa.net>
> To: <dinosaur@usc.edu>
> Sent: Saturday, March 03, 2001 8:37 PM
> Subject: _Scipionyx_ and diaphragms again
> 
> 
> > I was recently looking over the original
> _Scipionyx_ monograph along with
> > Ruben et al's Science paper regarding a possible
> diaphragm in the little
> > bugger and I was wondering if it has actually
> conclusively been resolved
> > one way or another with regards to the diaphragm
> issue.
> >
> > I remember that HP Jeff Poling had a page up on
> his site that featured a
> > compilation of different DML postings rebutting
> Ruben's paper, but I can't
> > seem to find it on the site anymore.
> 
> It is still there. For unknown reasons it just isn't
> in "Archaeopteryx,
> ancient birds, and dinosaur-bird relationships", but
> in "Miscellaneous".
> http://www.dinosauria.com/jdp/misc/lungs.html
> 
> > Oh and one final thing. What evidence do we have
> that theropods had an
> > avian respiratory system. What osteological
> markers were there? I mean the
> > pleurocoels would work fine just as weight
> reducers. Do we actually have
> > evidence that they played a part in respiration?
> 
> The pleurocoels (and analogous pneumatic holes in
> the pubis of
> *Archaeopteryx*, the ilium and furcula of the new
> carcharodontosaurid, and
> nearly all bones of recent birds) are weight
> reducers because they are
> filled with air. I've heard that an eagle's feathers
> weigh OVER TWICE AS
> MUCH as its skeleton. Now how can air get there if
> those holes and
> depressions aren't connected to the respiratory
> system?
>         An additional function is be cooling.
>         Several SVP meeting abstracts of the last 3
> years that I'm currently
> reading say that lots of dinosaurs couldn't breathe
> in enough air through
> their nostrils, the big ones not even when they were
> ectothermic! Also, I've
> so far seen only one solution to the question how
> long-necked sauropods
> could live at all: A long trachea means a large
> volume of air that is
> breathed in but doesn't reach the lungs. If maximum
> lung volume is smaller
> than trachea volume, the animal can never get fresh
> air into its lungs and
> _has_ never grown such a long neck. Giraffes have
> solved this problem by
> developing a thinner trachea -- this will evidently
> stop somewhere, i. e.
> before the 15-m-long neck of *Mamenchisaurus*, even
> if one doesn't take into
> account that a thin trachea means lots of friction,
> so breathing becomes a
> stressing exercise. If sauropods had air sacs, they
> had lots of additional
> volume for air, so a long trachea wasn't so much of
> a problem. Sauropods
> have lots of pleurocoels all over their vertebral
> columns.
> 


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