Re: Ectothermy?

["Larry Febo" <larryf@capital.net>]

{Ok! Ok! Dr. Holtz, I don`t want to start the debate right now, I need some
back-up references. But at least repy that I acknowledge your points, and
wilkl certainly consider them in my further research.} {Psst. I`m in these
brackets now. Trying to be creative here!}

-----Original Message-----
From: Thomas R. Holtz, Jr. <th81@umail.umd.edu>
To: larryf@capital.net <larryf@capital.net>
Cc: dinosaur@usc.edu <dinosaur@usc.edu>
Date: Thursday, September 03, 1998 9:24 AM
Subject: Re: Ectothermy?


>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! :-)

>{no serious comment here, I`ll refrain}

>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.

{so,(aside from skunk cabbages, you`re absolutely sure these groups have no
basic endothermic method going on? I personally don`t know, but maybe I`ll
find that out for sure too,}
>
>>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.

>{There should be some evidence to link them, don`t forget to allow for
quite a long period of divergence in these traits though}

>>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.

>{Funny,I have a copy of Bakker`s "The Dinosaur Heresies", and it shows a
"hypothetical  cold-blood" turning tail on a similar sized "hypothetical
warm-blood" pg.95!}

>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.

>{which,would make sense for the sauropsids in an arboreal enviorn.}

>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?

>{Yes, they would have to be ...to a degree.} {I don`t expect to find
evidence for each one.}

>>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 been trying to do that in my own mind all along. I keep looking for
the "negative evidence" and it comes up with loopholes. i.e. the fossil
evidence "shows that with Petrolacosaurus, began the diapsid condition in
the late Pennsylvanian, that`s one small group. If it weren`t found, then
we`d be considering the diapsid start at what? the early Permian? Why not
allow for some leeway in the other direction? Also, I was  at first ready to
chuck my whole idea when I realized...hey, if the diapsids were warm-blooded
from the start, then why are there cold blooded forms today! I was in the
dumps for half a week, till I noticed a diagram of heart structure which
shows reptiles with a partial  separation of the ventrical. Now I`m thinking
secondary ectothermy, with a vestigial structure,...unless, they are in the
process of re-evolving endothermy, which I consider unlikely, as the`re are
plenty of those around already as competitors.. I know this is just gleaning
over the basic facts, and it should be studied in more depth, and at all
levels. Hey, I`m just one person, and this subject toutches on many fields.
It sure is going to take some time to "hash it all out", but, I`m not the
kind of person who likes to take another`s word for it, so I guess I`ll just
have to find out for myself. Thanks (again) for the hints though!}

>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.

>{no kidding!}

>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
>
{P.S. If I find out anything major, I will let you know!}