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Re: _Scipionyx_ and diaphragms again



----- Original Message -----
From: "Miles Watson" <astute54@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Monday, March 05, 2001 2:37 AM
Subject: Re: _Scipionyx_ and diaphragms again


> Aren't all these points pointing to a Mesozoic
> atmospheric oxygen count of some 30%-35%,

Oxygen levels are thought to have risen to about 26 % in the MJ and to have
remained there to AFAIK the end of the Eocene, based on bubbles in amber and
paleosols. 30 -- 35 % may have occurred in the Carboniferous, though this is
crazily high, and Hollywood-style forest fires must have occurred all the
time. Well, high oxygen levels surely made breathing easier, but I can't do
the maths to calculate whether giraffes could evolve 15-m-long necks in an
atmosphere with 26 % oxygen -- let me doubt it as long as there's no
evidence to the contrary.

> more than
> twice the oxygen content that has been recorded in a
> major present-day city(12%-15%)?

What? IIRC the minimum requirement for humans is 13 %? (The mean recent
value is just below 21 %.)

> --- David Marjanovic <david.marjanovic@gmx.at> wrote:

[...]

> >         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.