Re: Insulation does not = "Warm-blooded"

["David Marjanovic" <david.marjanovic@gmx.at>]

> "David Marjanovic" <david.marjanovic@gmx.at> wrote:
>
> >Anyway, considering the fact that *Archaeopteryx* and all birds for
> > which feathers are known are insulated all over their bodies, none of
them
> > can possibly have been ectothermic, because insulation restricts heat
> > exchange with the environment.
>
> Ah, but as it restricts the ability to attain heat from the environment,
so
> too does it restrict the ability to lose heat to the environment.

AFAIK all endotherms except polar bears have methods for getting rid of
excess heat.

> So if your a
> fast living ectotherm covered in heat retaining feathers and your flitting
> about, then all the heat generated by those muscles (be they ecto or endo)
> would get trapped in the body, effectively removing the need to warm up
> ectothermically. The only problem then would be in keeping from heat
> exhaustion.

Indeed -- imagine an isolated ectotherm that has chilled out trying to warm
up in the sun. Will take quite some time, probably too much to let
insulation be an advantage.

> And besides, we have extant "cold-blooded" animals today with insulation
> (lamniforme sharks, _Dermochelys coriacea_, moths, bees and spiders).

The Great White (is it a lamniform? I don't know such things) has been found
to be homeo- and apparently endothermic, at least the specimen that has
swallowed a thermometer.
The leatherback turtle is the only known gigantotherm.
Several insects (I don't know for spiders) are actually endothermic, or
partly so.

> > About bones... some people think that enantiornithines were
> > ectothermic because of the LAGs (lines of arrested growth) in their
bones.
> > This conclusion has turned out to be nonsense, at least in hadrosaurs.
I'm
> > sure this has been discussed ad nauseam onlist; if you want, I can dig
up some
> > papers on this subject.
>
> Well, I dont' know if Rob would want them, but I certainly would. If
anything
> all these bone histology studies have shown is that they are useless in
> determining endo/ectothermy (or poiki/homeothermy, brady/tachymetabolism;
> whichever is more appropriate).

Coming.

> Jura - probably the only listmember who advocates bradymetabolic dinosaurs
and
> enantiornithines.

I'll dig up HP Paul and Leahy's Dinofest 1994 paper...