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RE: PLEUROCOELOUS VERTEBRAE IN SAUROPODS



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>From:  GSP1954@aol.com[SMTP:GSP1954@aol.com]
...
>You are confused. Animals thermoregulate! Giant reptiles might be able to be
>homeothermic by DELIBERATLEY retaining body heat at night, by minimizing
>blood flow to the skin. For giants with high metabolic rates to dump heat is
>merely a matter of flushing the skin with blood from the body core and
>letting the heat radiate into the cool night sky. Desert elephants up to 11
>tonnes do it all the time.

I am not confused that animals regulate their temperature.   I am
confused about what you mean by "store heat" and "dump heat".   Let me
clarify questions I asked:

1.  Does the core body temperature of elephants increase during the day
and then drop at night?

2.  If not, then what did you mean by "store heat during the day"?

3.  Is there is another "storage" mechanism, and if so what?

4.  Do you have any references to this so I don't have to bother you?

I am asking about elephants because you use them as a concrete example
of the mechanism you propose for sauropods.  Also, nobody has every
gotten a temperature reading from the inside of a sauropod, so they are
an interesting proxy.

Here is why I think these are interesting questions.  Animals
thermoregulate via controlling heat production (internal metabolism),
and by cooling mechanisms, (such as sweating, panting etc.).  Heat comes
from several sources, only some of which the animal can control.  Heat
comes externally from hot air or solar radiation, and internally from
digestion (or fermentation) in the gut or and muscular motion.   High
metabolism animals like mammals have a constant rate of internal heat
production, but if they do not cool adequately, they die. Some of the
cooling mechanisms are internal (regulating blood supply, sweating,
panting), some is behavioral (like finding shade during the heat of the
day).

As you point out in another message, some cooling mechanisms that
animals have access to are useless or even counterproductive once the
ambient air temperature is higher than body temperature.  In a similar
fashion, high humidity makes sweating or other evaporative cooling
useless.

The sauropod "heat problem" arises (in some people's minds anyway)
because of a concern that  unavoidable heat production would be greater
than the cooling mechanisms available to them.   One reason for this is
that the surface area to volume ratio decreases with size, making it
harder to vent internally generated heat to the outside.

I very much want to believe (i.e. understand) the mechanism you
proposed.   You propose that sauropod "store" heat during the day.   The
only reasonable interpretation of "store" that I came up with is that
unavoidable internal heat in excess of what can be vented via cooling
mechanisms would build up until night time.   At that point, cooling
mechanisms would be more effective (due to temperature drop and lack of
solar radiation), so simply flushing of blood in the skin could deal
with it.

I want to know how the heat is stored.  There are only limited
mechanisms to store heat - temperature increase (multiplied by a large
mass), phase change or chemical.  Which is it?  If there is no storage
mechanism then your explanation is simply wrong - or at least wrongly
stated.

I really don't mean to be dense, but saying again that elephants do it
all the time and it works great does not help.

Nathan

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