Re: Jurassic Park

[Scott A Hartman <ottscay@uwyo.edu>]

>>>fur and feathers... sloths, jaguars, apes, etc.  Not as large as
elephants
of course, but of substantial size.  So therefore it would seem that, in
theory anyway, we wouldn't find animals in tropical environments with
insulation, but the animals don't cooperate.  Those rascals.  <<<

I'm sorry I cut off the first part of that quote.  I'm not trying to quote
you out of context, and I'd ask anyone who hasn't been following this
thread to refer back to Peter's message prior to reading my response.

First of all, we would not restore tropical elephants as woolly.  That's
because an overly thick pellage would cause overheating (trap too much
heat).  It wouldn't be unreasonable, however, to restore them with a thin
water buffalo like pellage.  Of course that would still be wrong, and I'll
explain how we could have predicted that in a moment.  First though, I
want to point out that ALL tropical endotherms have insulation.  Every one
of them.  The point of insulation is to isolate oneslf thermally from the
environment, and it is important to remember that size can in and of
itself be a form of insulation.  Peter mentions that "large animals" like
jaguars, etc. have insulation (=fur).  All tropical mammals under 400 kg
(=850 lbs) have fur, and many larger ones do.  The purpose is to seperate
the skin from the sun.  Surface conditions (skin, rocks, etc) in direct
sunlight can be almost double the ambient temperature.  If you are really
big, then your very small surface area slows the rate at which heat is
transfered to your core, and you can radiate heat through evaporative
cooling at a rate fast enough toprevent overheating.  For animals much
less than a tonne, the heat gain is simply to fast, and melt down occurs.
So lion fur (which is short and "bristly"), keeps heat out, rather than
in.  Sun striking the fur is kept away from the body, and keratins much
much higher specific heat slows down the process of heating the body,
allowing endotherms much needed time out in the tropical sun. That's why
the animals you mentioned have fur.  And velociraptor was well within the
"small" animals range (as were oviraptor, troodonts, and compsognathids).
That's why all tropical endotherms have insulation and why all those
critters below 400 g in mass have fur or feathers. And elephants lost fur
9although it would confer some advantage) because the cost of producing
fur was higher the the extra time the large animals would be able to spend
in the tropical sun.

Scott Hartman