Re: Warm-Blooded debate

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

> From:          Dinogeorge@aol.com
> Date:          Fri, 20 Jun 1997 15:07:57 -0400 (EDT)
> To:            tons@ccs.netside.com, dinosaur@usc.edu
> Cc:            Dinogeorge@aol.com
> Subject:       Re: Warm-Blooded debate

> In a message dated 97-06-20 14:25:04 EDT, tons@ccs.netside.com (Michael)
> writes (responding to me):
> 
> << >   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. >>
> 
> Four-chambered hearts are >necessary< for any tetrapod to have long legs and
> an erect gait, because it separates the pulmonary circulation from the
> systemic circulation. This allows an elevated blood pressure in the systemic
> circulation while keeping the blood pressure lower in the lungs. A high
> pulmonary pressure would all too easily flood the lungs with blood and result
> in the premature death of the animal, which is why the pulmonary circulation
> must be kept quite separate from the systemic in erect animals.
> 
> Elevated systemic blood pressure allows the evolution of "verticality." All
> known terrestrial vertebrates, large and small, with three-chambered hearts
> or incompletely four-chambered hearts are sprawlers or slitherers, simply
> because they cannot muster the blood pressure required to bring blood back to
> the heart from erect limbs. I think the emergence of semi-erect therapsids in
> the Permian and archosaurs in the Early Triassic correlates well,
> phylogenetically as well as structurally, with the (independent) development
> of the four-chambered heart in those groups. For me, the
> quadricameral-heart/erect stance argument is a clincher.

I agree with you.  In fact, I don't think even a reptilian 
crocidilian heart would have worked.  Crocs have functional four 
chambered hearts, but the foramen of panniza is open during late 
systole.  Even in crocs blood from the right systemic arch mixes with 
that of the left.  If an animal had a high enough pressure too much 
blood would mix and the animal would have a fulltime left to right 
shunt with low O2 saturations.  This could even lead to aortic regurg 
into the right ventricle with sequalae although I'm guessing here.

It may take a while before I can get an answer on the elephants, but 
I do want to comment on what is known as heat windows.  This is 
partially what an elephant's ear is around the edges and where it is 
thin.  The edges of a rabbit's ears are the same.  Legs, the nose; 
anywhere blood vessels are near the surface and the animal has the 
capacity to regulate blood flow.  This is different from a 
counter-current exchange.  It is merely a way to take heat from the 
core and move it to the environment via the bloodstream if the animal 
is hot. ( Or keep blood away from the surface if it's cold.)

Someone joked about the long tail and necks of sauropods, but they 
would be a way to move heat away from the core to a more exposed 
place and would be heat windows.  The legs would act the same way. 

If sauropods could also regulate blood flow to the skin, then they 
could radiate more heat away.  

Someone mentioned radiation of heat away at night.  Camels can go 
further, by dropping their core temps below ambient temp and go into 
the day with a heat deficit.  This is known as limited heterothermy 
and is practiced by some small animals as well, but in very small 
time increments.

So there are ways, I think, for large sauropods to be endothermic 
without dropping dead from heat stoke.  There are other mechanisms 
for losing heat, but I'll save it until the next endothermy thread 
war.  

By the way, I could easily be wrong, but since no one knows.....


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