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Re: dinosaur endothermy (long)



From: GSP1954@aol.com (Greg Paul)

 > Feathered dinosaurs - ... In any case, the presence of a
 > feathery body covering if confirmed will be powerful evidence for
 > endothermy over a reliance on the environment for body heat.

Maybe.  This depends on the distribution of the feathers in the body.

So far I have only heard reports of feathers along the nape of the
neck and the back on this new possibly feathered dinosaur.  If this
is indeed the only part of the specimen with feathers, and if there
is no taphonomic reason to suspect preferential preservation, then
it is invalid to conclude endothermy from this evidence.

Feathers restricted to the back of the neck and torso can have only
one purpose, AFAIK, and that is display.  They would be very effective
for this purpose in that location, as they would have the effect of
enlarging the apparent size of the animal when erected (a very important
part of many agonistic display systems). Such a distribution would
cerainly be useless for insulation.

So, even here we must await a detailed analysis of the specimen. We
need to find out if the apparent limitation in feather distribution is
real or an artifact of preservation.

[Note, I do find the evidence for at least soem degree of endothermy
and tachymetabolism in most dinosaurs to be substantial.  The only
group that I have some doubts about is the sauropods, and even they
were probably tachymetabolic as young, and only switched to brady-
maetabolic style as adults].

 > Polar dinosaurs - It is true that the Mesozoic poles were not nearly
 > as harsh as they are today, but with long dark winters they were not
 > reptile heaven either.

Also, "not as harsh" still leaves things pretty cool.  The best estimate
I have seen for Late Cretaceous North Slope is an average annual temp.
of a few degrees above freezing.  With even modest seasonality this
still implies frost in winter, and even the summers are likely to
have been on the cool side, especially near the coast (where the
fossils are found).

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.