Re: Ectothermy?

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 06:58 AM 9/3/98 -0400, Larry Febo wrote:

>Yeah, Tom, I see what you mean. And what about the "hot blooded" tuna? A lot
>of research there.

And, of course, endothermic plants like the skunk cabbage.  Oh, there you
go: endothermy must be basal to Eukaryota! :-)

This is why it is important to keep things in mind of a detailed anatomical,
physiological, and phylogenetic context.  "Warm-bloodedness" in mammals,
birds, neoselachian sharks, tunas, skunk cabbage, etc. is NOT all the same
thing.  Functionally, it might be: energy generated by specialized
subcelluar structures (okay, I'm not certain about what tissues skunk
cabbages use to generate their heat).  Anatomically, though, these
structures are not the same in all these groups, nor are they behaviorally
the same: as I understand it, the sharks do NOT have an elevated metabolic
rate at all times; it is simply activated during certain behaviors.

>That`s why I tried to "qualify" my statement of one time
>development of endothermy to mean the giant leap to a brooding condition of
>whats classically known as "warm-bloodedness". Here I`m thinking bottleneck.
>Only one species making the transition to brooding behavior, and passing on
>the genes to all subsequent types.

If so, then a) the genetics for "warm-blooded" and associated traits in
birds and mammals would be paralogous and b) the subcellular structures used
to generate the heat would be homologous.  Are they?  Time to look into it.

>Probably talking anapsid to synapsid.
>With the subsequent benefits of ,(a tenfold? As stated by Chris
>Lavers),increase in metabolism, I don`t see how the diapsid line could have
>developed a similar condition, directly from the anapsids, in the face of a
>competing population of already warm-blooded synapsids.

Except, of course, as even Bakker admits, the "warm blood good, cold blood
bad" paradigm is a piece of crap.  Sure, elevated metabolism lets you do
lots of things for a longer period of time, but at an immense cost to the
amount of fuel (food) needed.  Bradymetabolic forms can do a lot better on
less than can tachymetabolic forms.

Additionally, thermoregulation is not the only difference between therapsids
and sauropsids.  For example, there is the ureatelic vs. uricotelic
metabolic difference (sauropsids are a LOT better at conserving water than
synapsids), differences in vision, etc.

Furthermore, are you asserting that basal (non-therapsid) synapsids were
endothermic?  Not all synapsids are _Thrinaxodon_ and _Cynognathus_: what
evidence would you use to suggest that _Cotylorhnychus_ or _Ophiacodon_ or
_Archaeothyris_ were endothermic?

>As an offshoot of
>the latter, yes. But as a completely independent development?,I don`t think
>so. (at any rate, this I will further research to the best of my abilities,
>and try to prove, or at least make a good argument for
>it)............................Dr Holtz???

It's also your job to try and disprove it, too.  Even a pseudoscientist can
keep on finding "evidence" for their pet theories: the way that science
differs from pseudoscience is that we conciously set up situations where our
hypotheses could potentially be disproven.

I've given you some major hints already.  For example, examine the genetics,
subcellular anatomy, and biochemical pathways of thermogenesis in birds and
mammals.  If they are not derivable from a common origin (i.e., if they are
not the same "thing", despite having the same function) then this would
support the idea that they are convergent (just as the anatomical
differences in the wings of birds and of bats support the idea that they are
convergent, even if they perform the same function).

Also, get to know the anatomy of basal diapsids and basal synapsids better.
These guys are better known then you might think: they simply don't get the
press that therapsids and advanced diapsids do.  Examine the evidence behind
the particular phylogenies produced for amniote systematics.  You cannot
just dismiss these a priori because they don't support your theory.

In other words, you have a lot of work ahead of you.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661