Re: Warm-Blooded debate

[Jonathon Woolf <jwoolf@erinet.com>]

bruce thompson wrote:
> 
>         There exists a scholarly monograph from about 15 years ago called
> _A Cold Look at the Warm-Blooded Dinosaur_  or something like that.  I
> never read it; could anyone supply the author(s)?

"A Cold Look at the Warm-Blooded Dinosaurs" is the published transcript
of the proceedings of a conference held around 1980.  I've never seen a
copy, it's apparently very rare, but it casts a very skeptical (one
could almost say jaundiced) look at the evidence as it was known then
for dinosaurian endothermy.  However, "the evidence for dinosaurian
endothermy" in 1980 amounted to upright posture, _Deinonychus_'s
obviously active nature, a few meager bone-histology studies, and
Bakker's admittedly tenuous predator/prey ratios.  No one had yet heard
of:

        * High growth rates in hadrosaurs 
        * Complex social behavior in hadrosaurs
        * Long-range migration by hadrosaurs and ceratopsids


>         I don't see why it is such a stretch for dinosaurs to have been
> ectothermic.  As evidenced by palm tree fossils near the Arctic Circle in
> Alaska, the earth was much balmier then.  Under such conditions ectotherms
> could have powered up much more cheaply than they can now, and could have
> been as active as we now suppose them to be.  

The difference between ectothermy and endothermy is not simply a matter
of "powering up."  Endotherms don't simply have more energy, they have
more endurance and a very different cellular chemistry.  Ectotherms have
no endurance because they can only generate energy anaerobically.  (A
lizard or a crocodile has to kill in its initial rush -- if it doesn't,
it has no energy left for a second attempt.  That's why all modern
reptiles are ambush hunters.)  Endotherms like mammals and birds can
generate energy both anaerobically and aerobically.  No anaerobic
organism could have developed the energy for hours of steady cruising at
ten or twenty strides per minute, as hadrosaurs and ceratopsids must
have done on their migrations.  

> Some dinosaurs did have sails similar to the pelycosaur Dimetrodon--why
> should those sails have been used for any different purpose?
> 

There's no certain evidence that sails in _Dimetrodon_ or _Edaphosaurus_
were primarily for thermoregulation.  Closely related pelycosaurs did
just as well without sails.  It's entirely possible that the sailbacks
had sails for display, like the frill on a frilled lizard.

-- JSW