Re: [Re: Insulation does not = "Warm-blooded"]

[archosaur@usa.net]

"David Marjanovic" <david.marjanovic@gmx.at> wrote:
> > 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.
++++++++++++++++++++++++++

True enough; most ecotherms have ways of dealing with excess heat removal
as well, though they aren't as sophisticated as mammalian sweat.

This does lead me to a side question: How do birds (especially large
active flyers like geese) dump excess heat? If I remember correctly, birds
don't sweat.

___________________________

>
> > 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.

++++++++++++++++++++++++++++++

I think you might have missed my point. I'm saying that with the heat
trapped on the body, while it would allow for a warm body, it could also
lead to heat stroke if not used carefully. Hence one reason why I wouldnt'
mind knowing how birds cool down as it might lead to an explanation on how
an ectothermic animal could cool down with a insulatory covering (besides
just being small enough to do it).

___________________________________
>
> > 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.

++++++++++++++++++++++++++

Yeah, the great white is a lamniforme and the one that I was talking about
(though I could have talked about makos as well which are also
lamniformes). More on the rest in a second.

______________________________

> The leatherback turtle is the only known gigantotherm.
> Several insects (I don't know for spiders) are actually endothermic, or
> partly so.

+++++++++++++++++++++++++++++++++++++

Okay, now we've reached the point where thermophysiology becomes a pain in
the @#$ to talk about.

Alright, so there are three main things about thermophysiology that one
must consider when talking about it: Endothermy/Ectothermy,
Homeothermy/Poikilothermy and Tachymetabolism/Bradymetabolism. All these
contribute to determining whether something is either "warm-blooded" or
"cold-blooded" and while we do have a few animals that fit all three
requrements, the majority are going to fall inbetween. In all the above
examples, we have line straddlers.

Yes, the great white is an endothermic homeotherm, but it can go months
without food and, thus, is bradymetabolic. Incidentally, most fish are
homeothermic.

_D.coriacea_ has enough fatty insulation to rival whales and along with
its countercurrent heat exchange system, is capable of maintaining a
constant internal temperature. It is homeothermic. Furthermore, it derives
the majority of its heat through internal metabolic processes. As such it
is also endothermic. But, oxygen intake tests have also shown that it is
bradymetabolic.

As for the arthropods mentioned all are probably endothermic (or partially
endothermic), but all are also obligatory poikilotherms and are
bradymetabolic.

So, not only is "warm-blooded" and "cold-blooded" a set of useless terms,
but using endothermy to be all encompassing for mammalian/avian leaky cell
endothermy doesn't work either. Nor does using ectothermy, for the same
reason.

To clarify my original post, I am saying that we have living
bradymetabolic and even poikilothermic animals that have insulation.

__________________________________


>
> > > 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
> anythingall 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...

+++++++++++++++++++++++++++++

Terramegathermy in the time of the titans right? Haven't read it yet, but
it is on my to do list as soon as I can get Dinofest papers.

In a perfect world, all papers would be online :)

Jura



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