Re: Warm-Blooded debate

["Michael" <tons@ccs.netside.com>]

>   Nevertheless, can you name me a fully erect, fully four-chambered-hearted,
> ectothermic animal? >>
> 
> Any adult sauropod will do, I'd say.

While you may be correct about the four-chambered heart(I suspect you 
are for several reasons), AFAIK no one really knows if dinosaurs had 
four chambered hearts.  I would be interested in discussing this with 
the list if anyone is interested.  
> 
> Indications are that adult fully endothermic sauropods would have overheated,
> particularly since they have no known anatomical structures with which to
> dump excess body heat, so full adult endothermy >likely< developed in the
> aforementioned lineage leading to birds >after< the sauropods diverged.

I still wonder about this.  Animals as large as elephants do not 
overheat, and their main source of cooling other than getting in the 
shade is radiation via the ears.  Of course they radiate heat back 
to the environment at night as large animals do as well.  I don't 
know if anyone has looked at the entire skin being a radiator in 
elephants or not (active not passive), but I'll find out and get back 
to you.  If a sauropod can use its circulatory system to radiate 
heat back to the environment via the skin as well, then I see no 
reason for them to overheat.  There are other mechanisms for 
dissapating heat as well and I will mention them when I get back to 
you.  I'm sure you already are familiar with this, but it might 
benefit some of the newer members of the list.

> It is possible, for example, that endothermy developed initially to allow
> >juvenile< dinosaurs to grow to half-adult size quickly. Then, as they
> attained maturity and giant size, endothermy gradually reverted to ectothermy
> (or gigantothermy) as the no-longer-needed growth rate slowed. I

I think this would be very unlikely.  Any animal that had an 
endothemic metabolism would probably be stuck with it.  There are 
too many cellular, organ, and endocrine differences for me to imagine 
this all turning off although it is an interesting concept and I 
guess possible.  Are there any extant organisms that would qualify?
> 

As always, this is only an opinion, subject to
retraction and recall without notice, and with 
due respect to others opinions.

Thanks,

Michael Teuton MD