Re: egg development and O-2

[Phil Bigelow <bigelowp@juno.com>]

I haven't read their paper yet (so maybe my questions are dealt with
there), but regarding the egg clutch survival issue:

Unless the atmospheric change was geologically instantaneous, it may have
had little effect on survival or mortality.  If the +/- O2 change
occurred over a period of a couple hundred thousand years, it could give
selection enough time to offset the effects of increased/decreased O2. 
In the case of falling O2 percentage, thinner membrane, increase in
membrane permeability, and decreased % of calcite crystallites in the
shell could all be selected for.

Test:
Has anyone compared the pore diameters of fossil hard-shell archosaur
eggs (pick a group) over geologic time?  If so, then does pore diameter
correlate with presumed O2 percentage at any given time?

There must have been at least a few taxa around at the Permian-Triassic
boundary that layed hard-shelled eggs.

Regarding why paleo partial pressure of O2 isn't discussed in the
literature:  Just a guess, but maybe because it would be hard/impossible
to test a hypothesis based on the concept.  I know of no fossil imprint
that ancient O2 partial pressure would leave behind. 

<pb>
--

On Thu, 04 Aug 2005 13:29:26 +0100 Mike Taylor <mike@miketaylor.org.uk>
writes:
> > Date: Thu, 04 Aug 2005 06:03:28 -0600
> > From: Ken.Carpenter@dmns.org
> >
> > [John Vanden Brooks] mentor, Robert A. Berner, the Alan M. 
> Bateman
> > Professor of Geology and Geophysics at Yale, characterized the 
> range
> > of atmospheric oxygen levels over multimillion year times scales,
> > and established an upper value of about 31 percent oxygen, and a
> > sharp decline near the Permo-Triassic boundary to about 12
> > percent. Earth's current atmosphere is about 21 percent oxygen.
> 
> Ken (and others),
> 
> Any idea why people always talk about the _percentage_ of oxygen in
> the atmosphere?  I'd have thought that the partial pressure would 
> be
> more important -- e.g. if the oxygen proportion fell from 20% to 
> 15%
> but the total atmospheric doubles, then, wouldn't the partial 
> pressure
> rise to 30% of the old total pressure (i.e. 1.5 times the old 
> partial
> pressure)?
> 
> Or is total atmospheric pressure constant because it's proportional 
> to
> g, or something?
> 
> Thanks.
> 
>  _/|_  
> ___________________________________________________________________
> /o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  
> http://www.miketaylor.org.uk
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> 


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