-----Original Message-----
From: Robert Clements <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Cc: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Thursday, December 07, 2000 11:54 PM
Subject: Re: On The Rise of Oxygen...
>
>[EMAIL PROTECTED] wrote:
>
>>
>> f) here's a somewhat unrelated question: what did Dinosaurs
breath?
>> Could the air have been thicker then, perhaps with somewhat exotic
chemistry
>> to it? How else to explain 2' dragonflies, and 80' brachiosaurs...
'heavier'
>> air might explain how a 2' dragonfly still could acheive loft, and how
>> dinosaurs could supply enough oxygen through those tiny heads to feed
such a
>> massive body.
>>
>> Any ideas or critiques out there?
>>
>> -- JHB, the gadfly
>
>No significant difference in the oxygen content of the atmosphere following
the
>Permian extinction (ie, the Mesozoic; which became the age of the
dinosauria);
>although the planet was somewhat warmer... even in antarctic Australia,
many
>species survived months of total darkness with little difficulty. Although
the 2'
>dragonflies may have first appeared during a period with more user friendly
>atmospheric conditions than currently, they were still alround in the early
>Mesozoic, when the conditions were much more contemporary.
>
>The real explanation for the 2' dragonflies & larger sauropods such as
>Seismosaurus or Argentiosaurus (both of which make the brachiosaurs look
like
>anorexic midgets) is much simpler. There's a basic rule in biology that
says: all
>other things being equal, its better to be big than little.
>
>Nowadays, all other things are not equal - mostly due to human greed - &
being
>large is a major disadvantage; but when the big dragonflies were around,
they
>owned the skies; & as a result could survive quite comfortably despite
their
>being almost certainly a fairly awkward flyer. When a new & more effective
design
>for flight - the pterosaurs - appeared, the dragonflies quickly vanished; &
the
>ptersoaurs grew enormous (Queztalcoatlsaurus had a bigger wingspan than a
cricket
>pitch (21m)). Pterosaurs were also not ideal flyers, though; & when good
bird
>designs took to the air in the Creataceous, the flying reptiles didn't last
very
>long; & were probably pushing extinction long before the Chicxulub impact
event.
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 are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED]
Project information and list (un)subscribe info: http://klx.com/europa/
