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Re: Climate change



>Don't forget that a climate change would be much more likely to affect small,
>delicate animals than the big ones, like dinosaurs. If the global temperature
>drops 20 degrees, for example, who would survive, a 30-ton brachiosaurid or a
>6-ounce salamander? The brachiosaurid can pick up and move hundreds of miles to
>the south (or north) to get to a warmer environment, but the little salamander
>has to stay there and freeze. As Bakker once said, "It's cheap to be big."

Ah yes, but Bakker was only half right. It is indeed "cheap to be big",
*but only if the ambient temperature is fairly constant*, i.e. as long as
the day/night temperatures do not fluctuate very much.  In the Mezozoic the
global climate was considerable more ameliorated (similar everywhere) than
it is today (greenhouse phase compared with todays icehouse phase) - where
sub-tropical conditions may have extended as far as approx. 60 degrees
north.  Then, day/night temperature fluctuations were fairly small over
considerable areas of the globe, making gigantothermy a viable strategy.

However, with the major climate shift towards the end of the Mesozoic (for
whatever reasons), the broad, ameliorated, global climatic zonations
collapsed, resulting in the expansion of the temperate zones - complete
with their more varied day/night, summer/winter temperature range.

Gigantothermy is fine if the ambient temperature doesn't fluctuate much,
but once it does, gigantothermy can be a death sentence. Whilst it is true
that an advantage of gigantothermy is that the body cools very slowly and
the core temp is thus protected, it also means that the body heats up
slowly and once the core temp starts to be affected, it is hard to re-heat
- especially if metabolism is only partially aiding the heating process.
The result would be that the big dinos would be forced into the narrower
tropical/subtropical zones.  But the whole supporting ecosytem was in
collape by then.

Small animals have the advantage of either:

1) nesting - i.e. hiding in a burrow or some such *insulated* hiding place
- to see out the coldest temperatures, perhaps even in a torpid
semi-hibernating state.  This would have been impossible for giant forms
because there just weren't any nests big enough.

2) wear a winter coat - i.e. have a fur or feather covering.  Again a
strategy denied giant forms.  Why?  Because as a organism increases in
size, the amount of heat produced via metabolism increases at a greater
rate than the surface area available to release the heat.  Thus the very
largest forms *cannot have any body covering* because that would interfere
with the loss of body heat, making it harder to loose heat and resulting in
the body metabolism literally cooking the animal from the inside.  By the
time they realized that wearing a fur coat or a feather stole was a good
idea, it was too late!

Chris

cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
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Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.