Re: Warm-Blooded debate

[Dinogeorge@aol.com]

In a message dated 97-06-19 21:55:40 EDT, NJPharris writes (quoting me):

<< >  This, rather than
 >  endothermy--which developed much later, perhaps only in the theropod
lineage
 >  that eventually evolved into birds--
 
 Whose words are these?  If they are yours, how do you know this?>>

My words. Perhaps I should have said ">likely< developed much later." See
below.
 
<< >  was necessarily responsible for
 >  dinosaurs' erect stance and cruising ability.
 
  Nevertheless, can you name me a fully erect, fully four-chambered-hearted,
ectothermic animal? >>

Any adult sauropod will do, I'd say.

By the way, I'm not interested in going around in circles over dinosaurian
endothermy. As I've said before, there is presently >no way< to resolve the
question satisfactorily. To do so, one would have to go back in time and do
an extensive series of thermal measurements of living dinosaurs belonging to
several different clades. Every argument pro endothermy has an equally
convincing argument contra endothermy, or at least enough counterexamples to
make the argument useless.

All we know is that modern birds are fully endothermic, so complete
endothermy must have developed >somewhere< in the lineage leading to birds
from the common ancestor of birds and crocodiles (which aren't endothermic).
Indications are that adult fully endothermic sauropods would have overheated,
particularly since they have no known anatomical structures with which to
dump excess body heat, so full adult endothermy >likely< developed in the
aforementioned lineage leading to birds >after< the sauropods diverged.

It is possible, for example, that endothermy developed initially to allow
>juvenile< dinosaurs to grow to half-adult size quickly. Then, as they
attained maturity and giant size, endothermy gradually reverted to ectothermy
(or gigantothermy) as the no-longer-needed growth rate slowed. If so, full
endothermy in adult birds would be a neotenous feature exapted for efficient
powered flight.

No way to confirm this scenario, but it fits the known growth-rate profiles
of dinosaurs as well as any.