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Re: _Scipionyx_ and diaphragms again
----- Original Message -----
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".
> 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.