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Re: egg development and O-2
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.
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.
On Thu, 04 Aug 2005 13:29:26 +0100 Mike Taylor <firstname.lastname@example.org>
> > Date: Thu, 04 Aug 2005 06:03:28 -0600
> > From: Ken.Carpenter@dmns.org
> > [John Vanden Brooks] mentor, Robert A. Berner, the Alan M.
> > Professor of Geology and Geophysics at Yale, characterized the
> > 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
> more important -- e.g. if the oxygen proportion fell from 20% to
> but the total atmospheric doubles, then, wouldn't the partial
> rise to 30% of the old total pressure (i.e. 1.5 times the old
> Or is total atmospheric pressure constant because it's proportional
> g, or something?
> /o ) \/ Mike Taylor <email@example.com>
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