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

[archosaur@usa.net]

"Demetrios M. Vital" <vita0015@tc.umn.edu> wrote:
> Jurassosaurus wrote:
> > 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.
> 
> -and-
> 
> David Marjanovic wrote:
> > Elephants are not gigantothermic, and terrestrial elephant-sized
> "reptiles"
> > (meaning "animals that Linnaeus would classify as reptiles if he'd see
> them
> > alive") are probably impossible. See my next post...
> 
> Really?  I was under the impression that surface area to volume was the
> determinant of gigantothermy.  I suppose I'll wait for this next post,
> though, before I ask for clarification...which just arrived in my inbox,
> coincidentally.
++++++++++++++++++++++

Heh, apparently being a leatherback is the requirement for gigantothermy :)

_______________________

> 
> Jurassosaurus wrote:
> > > To clarify my original post, I am saying that we have living
> > > bradymetabolic and even poikilothermic animals that have insulation.
> 
> Bumblebees and hummingbirds, among other examples.
> 
> Jurassosaurus wrote:
> > I know of no good heat trapping comparison studies on these two.
> >
> > I wonder if anyone has even bothered with that one yet?
> 
> Well, using the Heinrich data that I wrote to you about (from _Bumblebee
> Economics_), we see that the insulation on bumblebees increases body
> temperature by 65-75%.  All you need are the numbers of mammal body
> temperatures with or without hair for a very rough comparison.

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

I'll look into it.


_____________________

> Jurassosaurus wrote:
> > 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(s) 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).
> 
> Thanks for catching me on that.  It was really easy to make that       >
statement, which gives me  newfound view of how easy it is for other   >
people to make this same mistake.  I was incorrect, that is             >
nonevidence, and I recant what I said.  As always, "absence of evidence > is
not evidence of absence."

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

*sniff* *sniff* hmmm, I smell foreshadowing >:)

_________________________

> Jurassosaurus wrote:
> > What
> > I don't see is any living examples of an animal that has leaky cell
> > endothermy and no insulation to hold it.
> 
> Now its my turn: "absence of evidence is not evidence of absence."
> Especially for organisms that may have existed in the past compared to
> extant organisms.

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

True, and I did see this coming when I posted it. I was going to put a little
disclaimer involving abiogenesis, but I was afraid it might be too confusing.

Well here goes anyway:

The problem with this scenario is the same that the RNA world abiogenesis
scenario faces. The environment conducive to making alife is mostly gone now
and even if it could happen, all the living forms today would outcompete it
before it had a chance (probably). As such, we can only speculate and theorize
on how this might have happened, knowing that the chances of anything like
this now would be extremely unlikely.

So yeah, L.C. endothermy might have arisen before insulation, and become so
prolific that all L.C. endothermic, non-insulated animals might have been
outcompeted thus leaving no living examples to use.

Oh well, at least with living examples of the opposite, we know that
insulation before L.C. endothermy is at least possible.

_____________________________

> Jurassosaurus wrote:
> > Forever the thorn in my side eh? :)
> 
> If by "thorn" you mean, "someone who has learned very much from you and > is
trying to glean as much knowledge as possible, including debating    >
skills," then yes! :)

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

At least I know you'll keep me honest :)

__________________________

> 
> Jurassosaurus wrote:
> > 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).
> 
> I'm not sure I totally disagree with you.  I think my biggest issue (at >the
moment) is the generalization of all non-avian dinosaurs and
> enantiornithines into bradymetabolism.

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

I try not to generalize, it's just that thermophysiology is such a pain in the
%$#% to talk about because metabolism is a spectrum. Technically not all
"cold-blooded" animals are bradymetabolic (e.g. caterpillars are
tachymetabolic animals, which allows for their rapid growth rates. Tadpoles of
certain amphibian species might be tachymetabolic too).

I believe that L.C. endothermy didn't show up in birds until the
enantiornithines (i.e. it probably showed up in some enantiornithines). I
don't think all enantiornithines were L.C. endotherms though. Of course since
enantiornithines were the sister group to neornithines it doesn't help much
with extant avians. I do think all Neornithines were L.C. endotherms, but I
don't know enough about them to say much more. I will say, though, that I
don't believe that archaeopteryigiformes like _Archaeopteryx_ and _Rahonavis_
were L.C. endotherms. Everything after them gets confusing.

__________________________________

> 
> Can you clarify then, for me?  Does bradymetabolism imply ectothermy in
> animals larger than hummingbirds? 

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

No, leatherbacks are many times larger than the largest hummingbird and are
not ectothermic. Nor are lamniforme sharks, tuna, varanids (partial
endotherms) and some python species during egg incubation.

__________________

> Does bradymetabolism imply low rates of
> activity, stereotypically "reptilian" activity levels (notice I said
> "stereotypically")?  

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

You mean like sprawling, swamp dwelling sauropods and scavenging theropods? I
think that in popular imagination it does, but in reality a bradymetabolism
doesn't hinder any of the proposed lifestyles of dinosaurs, so I don't see why
the stereotypical reptilian activity levels should ever come into play.

_________________________

> What are the repercussions of your argument on other
> aspects of dinosaurian physiology?

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

Well, for one, it allows dinosaurs to survive extreme amounts of damage. For
instance, Larson asserts that _T.rex_ was a familial animal because without
someone getting Sue food while it had that broken leg, it would have died. If
Sue was bradymetabolic then its metabolism would slow with the decreasing
amount of activity, allowing the tyrannosaur to heal the leg without the aid
of other tyrannosaurs to get it food. When Sue could move again, its
metabolism would pick up again and life could go on. 

Note: That was all speculation based off of how extant reptiles handle
seemingly impossible amounts of damage. Regardless though, it was still all
speculation.

Anyway, that is one example.

Jura

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

http://reptilis.net

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