Re: CROCODYLOMORPH ENDOTHERMY

[cpretzma@magnus.acs.ohio-state.edu (Chip Pretzman)]

Dinogeorge wrote, on 1-31-96:
>Right. But the endothermy surely came later. We're talking about _necessity_
>here. Endothermy should be considered an evolutionary improvement to an
>already active lifestyle.
>
>

Warm-bloodedness, or endothermy, or homothermy or whatever also occurs in
some plants, so endothermy is probably not an improvement over an already
active lifestyle.  Some fish and maybe even some reptiles have acquired
functional endothermy, not full blown endothermy seen in birds and mammals.

My arguement for endothermy in dinos is that warm-bloodedness conveys so
many advantages to the organism that once an organisms acquired it, it would
rapidly outcompete its neighbors. Once endothermy occured, it was a bad day
for ectotherms. Dinosaurs had to outcompete most everything else to become
so succesfull for so long. They also co-existed with mammals and in order to
compete, probably had to be warm-blooded.  Really big dinos may have been
functionally endothermic because of their big body size.

If dinos were cold blooded, especially the small lithe ones, and had to lay
around in the sun for an hour or so to get going in the morning, they would
have been eaten. Probably by something small fast and furry, like a mammal.

Of course, ectotherms exist where they can outcompete endotherms.  Like in
hot climates where they warm up quickly.

Of course, endotherms exist in temperate climates, but nowhere near the
diversity that occurs in hotter climes.  Pangaea was predominately a
temperate climate, and more diversity would have been seen among the
endotherms.  I don't insist upon the strength of this argument to prove that
dinos were hot-blooded, but I can see no way they could have dominated the
ecosystem at that time if they were not.

-Chip Pretzman
Dept. Molecular Genetics
Laboratory of Evolutionary Genetics
The Ohio State University