-----Original Message-----
From: Robert Clements <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Cc: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Friday, December 08, 2000 1:43 AM
Subject: Re: On The Rise of Oxygen...
>
>Bruce Moomaw wrote:
>>
>> While I didn't know that the huge dragonflies held on into the early
>> Mesozoic, Clements' explanation has a big problem: why didn't the equally
>> huge crawling bugs of the Carboniferous Era hold on? They didn't have
the
>> clumsy-flight disadvantage of those huge dragonflies -- there's no
obvious
>> competitive-evolutionary reason why we don't still have two-foot
cockroaches
>> and 6-foot millipedes around. It seems likely that the decline of the
>> oxygen level in the early Mesozoic was indeed the key factor in nudging
>> these horror-movie refugees into extinction.
>>
>> Of course, one qualification: there are still a few giant gadflies
around.
>> Witness Clements.
>>
>> Bruce Moomaw
>
>You're taking me way back into biomechanical studies i thought i forgot
decades
>ago; but there are disadvantages to being a large hard shelled bug of any
kind.
>One of the bigger is respiration; which is why the O2 rich periods of the
>Palezoic suited our not-so-little frees to a t (or more precisely: 02); but
in
>the absence of competition capable of perhaps literally stomping these
critters
>out of existance, big bugs would still be around... qv, the weta in NZ;
which i
>think is one of the biggest land arthropods surviving; & which did survive
in
>the highly anomalous New Zealand paleoenvironment.
>
What in the world is a weta?
More generally, in today's lower-oxygen environment, big bugs must be much
more sluggish, which puts them at a severe disadvantage both in chasing prey
and in surviving predation themselves. A few of them still hold on in very
specialized ecological niches, but it still seems overwhelmingly likely that
what wiped out almost all of them -- either directly or indirectly -- was
that O2 loss. (Note, by the way, that almost all the surviving big
arthropods are aquatic, simply because they don't have to carry their own
weight around.)
I just had a thought: Would the higher O2 level of the Permian mean that the
worldwide fires set by an asteroid impact would be much more severe back
then -- and could this possibly explain why the Permian extinction was so
much more complete than the Cretaceous one? (It wouldn't directly explain
why the Permian marine extinction was also worse; but maybe the increased
smoke -- and the resultant natural "nuclear winter" effect -- would also
have been more severe.)
Bruce Moomaw
==
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