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

[archosaur@usa.net]

"Demetrios M. Vital" <vita0015@tc.umn.edu> wrote:
> David Marjanovic wrote:
>
> > > Several insects (I don't know for spiders) are actually endothermic, or
> > > partly so.
>
> [snip]
>
> Jurassosaurus replied:
>
> > As for the arthropods mentioned all are probably endothermic (or
> >partially endothermic), but all are also obligatory poikilotherms and
> >are bradymetabolic.
>
> If they have no "choice" but to be poikilotherms and bradymetabolic,
> they aren't great examples, then.

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I disagree (bet you didn't see that coming :), since they have no "choice"
they do serve as telling counterexamples of animals that have insulatory
covering without developing a tachymetabolism.

___________________________
>
> Can we assume that obligatory poikilothermy exists at insect sizes while
> obligatory gigantothermy exists at  elephant size?

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

I'd think so; at least all extant examples seem to appear that way. Course
it would help if we had a few extant elephant sized reptiles around to
compare this with.

_______________________


>
> > To clarify my original post, I am saying that we have living
> > bradymetabolic and even poikilothermic animals that have insulation.
>
> Is subcutaneous insulation equable to integumentary insulation?

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You'd have to define integument (as the chitinous bodies of insects are
often referred to as integument), but I'd say yes. In the cited examples,
the hair serves the same function that it does in mammals, though I know
of no good heat trapping comparison studies on these two.

I wonder if anyone has even bothered with that one yet?

______________________________


> What I'm trying to say is this:
>
> Insects are obligatory poikilotherms, thus their use as an example for
> enantiornithines and non-avian dinosaurs,  which are not necessarily
> poikilothermic (hence this discussion) is very limited, indeed.  The
> other two examples Jurassosaurus gave are large-sized marine animals.
> Water, of course, saps heat much more than air, by levels of magnitude.
> So they are obligatorily insulated, endothermic, and the turtle, at
> least,is also bradymetabolic.

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

Ah, but both the white pointer and the leatherback evolved this fat to
deal with the cold waters that they frequent. We don't find this fat on
all fish and even the arctic antifreeze fish don't seem to have it (which,
of course, begs the question of how these animals even move).

The leatherback and the lamniforme are not one of millions, but one of
dozens of bradymetabolic creatures that found the benefits of insulation
without increasing their metabolisms, so it's not like one can say "but
all aquatic animals have this," these sharks and that turtle have the kind
of fat one would expect to find in whales and seals (especially the
turtle), hence, why they are so intriguing to the question at hand.

__________________________________________


>
> But there are no examples of terrestrial, insulated (by fat or
> integument, which are not as comparable, I think, as you say),
> bradymetabolic, poikilotherms.  That lack is an argument itself for
> terrestrial insulatory integument being obligatorily in concert with
> endothermy.
>

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Is it now? Sounds a lot like the feathered _Velociraptor_ subjects;
absence of evidence and all. In fact, isn't this the same type of argument
that listmember blasted Ruben et al for when it came to turbinates (i.e.
no living ectotherm has'em, all [most] endotherms have them, dinosaurs and
early birds didn't have'em therefore they were bradymetabolic).

Besides, I already mentioned the arthropods, which are terrestrial,
bradymetabolic poikilotherms, though I'm sure you were hoping for
something that was at least within vertebrata, in which case, I'll see
what I can do.


Anyway, the argument, as it seems to stand, is that leaky cell endothermy
evolved first and insulation (fatty or integumentary) came later.

Well I say just the opposite, that insulation had its benefits prior to
leaky cell endothermy and I even have living examples to back it up. What
I don't see is any living examples of an animal that has leaky cell
endothermy and no insulation to hold it. The only possible examples I can
think of is naked mole rats, and last I heard, they were secondarily
ectothermic, poikilothermic, bradymetabolic or whatever the hell the term
for non-leaky cell endotherm is.

__________________________________

> -Demetrios Vital
>
> P.S.: I don't give up, Jurassosaurus :)

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

Forever the thorn in my side eh? :)


Oh and for the record, it is bradymetabolism that I am arguing for. I'm
pretty sure most, if not all, dinosaurs were homeothermic and even
endothermic. Whether or not they achieved it through thermoregulatory
means, gigantothermy or leaky cells as well remains to be seen (probably
the wrong choice of words there considering the subjects at hand).

Jura





Jurassosaurus's Reptipage: A page devoted to the study of and education on,
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