Endothermy speculation

[gmbra@cygnus.uwa.edu.au]

Hello, all
Bit of speculation that occured to me as I was going back over some posts
on endothermy.
Given that body temp needs to be maintained relatively constant at least in
part because critical enzymes in metabolic pathways have a fairly narrow
operating range, I wondered why this should be so. The ideal situation in
theory would seem to be metabolic systems that work most efficiently at
ambient temperature, as this removes any need for drastic temp regulation.
For todays humans, that max efficiency temp is around 37 C, considerably
higher than ambient temp even in the tropics. The basic metabolic processes
that necessitate such a temp go back a long way, evolutionarily speaking.
My first question then is - did they first evolve to function most
efficiently at the then ambient temp? If so, was the temp at that time
(whenever it was) as high as 37 C? If it was, then the problems of temp
regulation for endotherms stems from a subsequent decrease in ambient temp
which has not been compensated for by adaptation. If the temp was not that
high, then did the metabolic processes originally function maximally at a
much lower temp (say 25 -30 C)? If this was the case, then for reasons
unknown (?) these processes have since changed their temp maxima, and the
question arises - when and in what fashion did the change occur? The
question for dinosaurs becomes something like - did they exist in a
situation where their metabolic processes did function best at the then
ambient temp? THis would presumably have a large impact on the amount of
energy (and hence food intake/oxygen intake) required for them to maintain
homeothermy.
Does anyone have any data pertinent to this speculation, or indeed, any
comments at all (polite, of course - remember the list rules!)
Graeme Worth