Warm -vs- Cold Blooded

Yes here I go again with YET ANOTHER thing I learned in school that is wrong.

I learned mammals and birds are warm blooded and everything else is cold blooded. Now I read some fish and reptiles aren’t. I can’t find a source to state which fish and reptiles are though. Any help??

I am not aware of any. I find it difficult to believe that any fish would be homeothermic – it would be very difficult for that to evolve in the water, because water conducts heat much better than air does.

As to reptiles, most paleontologists now believe that dinosaurs were warm blooded, but most of them also believe that dinosaurs ought not be classed as reptiles, but in a new all-dinosaur class. Some have even gone so far as to say that birds should be demoted and made a subclass of dinosaurs.

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

Reptiles? I can’t think of any off-hand. However, tunas are functionally warm-blooded. Their muscle activity keps them at a higher temperature than ambient.

Dr. Fidelius, Charlatan
Associate Curator Anomalous Paleontology, Miskatonic University
“There’s a Seeker born every minute.”

Yeh, what he said. And some believe the dinosaurs were the same way. That is, they weren’t endothermic in the same way mammals and birds are, but they did maintain a higher body temperature then ambient by being physically active.

The usual definition of “warm-blooded” is homeothermy, keeping the body at a near-constant temperature no matter whether the environment is warmer or colder.

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

Most dinosaurs claimed to be heterothermic, but some were outed as homoeothermic.

(Sorry…couldn’t resist it!)

This can be resolved by realizing that the phrase “warm-blooded” is totally misleading. The actual physiological distinction is pretty cut-and-dry.

Homeotherm: an organism that can maintain its core temperature solely through metabolism.

Poikilotherm: an organism whose core temperature either fluctuates, or is maintained but NOT by metabolism.

Accordingly, there are a LOT of warm-blooded poikilotherms, tuna among them, and many desert reptiles, whose core temperature stays quite steady for long periods, but requires some modifiying activity (e.g., muscle activity) in order to do so. The body temperature of a honeybee drone never drops below about 98 degrees, and gets as high as 120 degrees. Yet, they are poikilotherms, because all that heat is generated by muscle contraction and NOT metabolism. Calling them “cold-blooded” is plain foolish use of terminology.