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Re: Cold-blooded vs. warm-blooded (LONG REPLY)



Barbara, Kendall, et al:

    I've copied a portion of a training summary I produced for a class about
dinosaurs several years ago.  (I've posted this list about 2 years ago).  It
contains all sorts of "thermies" ...   My personal view is that dinosaurs
ran the gamut from what we call "cold-blooded" to what we call
"warm-blooded", depending on many factors.

        Allan Edels

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Some finer details about "Warm-blooded"-ness versus "Cold-blooded"-ness.

 Definitions -

A."Warm-Blooded" -

Endothermy - internal regulatory system that maintains its temperature at a
constant level.


B."Cold-Blooded" -

Ectothermy - body temperature regulated by use of the outside (ambient)
temperature, usually behaviorally. Note: Many ectotherms can "feel" quite
warm to touch.

C.Homeothermy - maintenance of a constant "high" body temperature.

Note: All endotherms are homeotherms, but not all homeotherms are
endotherms!


D.Poikilothermy - wide variation of body temperature in response to
environmental temperature.


E.Tachymetabolic - animals that maintain their metabolic rate at a high
level all the time.

F.Bradymetabolic - animals that have a slow, or low, resting metabolism.


 In general:


A.An endotherm is also a homeotherm and is tachymetabolic.

B.An ectotherm is also a poikilotherm and is bradymetabolic. Note that under
"ideal" circumstances, many ectotherms can be homeotherms behaviorally.


C.But NOT always! -

1.Bats: Endotherms, not exactly homeotherms, and not always tachymetabolic.
They lower their metabolism at night or when food is not available.

2.Hummingbirds: Similar to bats, their metabolism drops to near "reptilian"
levels at night when they don't feed - their body temperature actually
approaches ambient temperature. Some people think that they should be called
"Heterotherms".

3.Australian Monitor Lizard - They can shift blood from their limbs to the
body-core when the outside is very cold. The limbs will then cool down in 15
minutes, but the body can take 7 or more hours to cool down. Many reptiles
can and do do this. Monitor lizards are very slightly endothermic.

4.Some sharks and tuna can keep their body temperature higher than the
surrounding water via muscular action, retia and arterial-venous
counter-current heat exchange.

5.Some snakes stay warmer than the surrounding air via muscular
contractions. This is usually done to keep eggs warm.

6.The Leatherback Turtle can keep the center of its body 18 degrees C. above
the surrounding water temperature via circulatory shunts, vaso-constriction,
and arterial-venous counter-current heat exchange.

D.It is possible that dinosaurs had some of the above properties, similar to
modern homeotherms, yet still remained ectothermic.


E.Most paleontologists think that the larger dinosaurs were "mass
homeotherms" - the large mass of the animals kept them warm. Nicholas
Hotton, III calls dinosaurs "the happy wanderers", because he feels that
they kept moving from place to place to maintain their food supply as well
as their temperature.


F.Some scientists say that because of mass homeothermy, large dinosaurs
would have generated internal heat as if they were "warm-blooded" as today's
mammals. However, extinct elephants and rhinoceroses (from the Miocene era
in India) were some 18 feet tall at the shoulder, which is nearly
dinosaurian in size, and these were definitely mammals. Note, though, that
giant mammals need to fluctuate their body temperature in hot climates. The
Miocene giants may have operated under a different climatic situation than
the Mesozoic giants.

1.Some dinosaurs had spikes, plates, frills, and/or large nasal cavities
that may have acted as heat exchangers, helping to warm or cool their
bodies. (These could have merely been used for sexual display purposes, or
for defensive purposes. Of course, they could have served multiple purposes
at once). The long necks and tails of the sauropods may have acted in these
ways as well.


G.Dinosaurs may not have required endothermy to remain at a constant
temperature because the ambient temperature during the Mesozoic (the age of
dinosaurs) was generally much warmer than the current climate, and remained
at a high level year-round. Very cold winters were almost non-existent.