[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Lotsa 'thermies..... (LONG Reply)

Caleb, et al:
    I have copied a portion of a training summary I produced for a class about dinosaurs several years ago.  I doubt that it contains all the "thermies" that you are looking for, but it does have a few... 

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. Cold winters were almost non-existent.
-----Original Message-----
From: Doug Lewis <dwlewis@rmii.com>
To: dinosaur@usc.edu <dinosaur@usc.edu>
Date: Saturday, February 14, 1998 6:13 AM
Subject: Lotsa 'thermies.....

SNIP< ....So, would anyone out there care to list the other 'thermies and describe them briefly. ... >SNIP
                        Happy Valentine's Day To All,