Re: CROCODYLOMORPH ENDOTHERMY

[tonyc@foe.co.uk (Tony Canning)]

On Wed 31 Jan 1996 Nick Pharris wrote:


> 
> There are plenty of researchers out there acting like we should assume 
> ectothermy for dinosaurs until endothermy is proven without a doubt.  We 
> will never know for sure, as Dinogeorge said, and I do not believe it 
> will hurt anything if I continue to believe that all dinosaurs were 
> endothermic until ectothermy can be proven beyond a doubt.  The evidence 
> just seems to make more sense that way.
> 

That's fair enough, but, as Nick says, many researchers have looked at the 
evidence and come to precisely the opposite conclusion, e.g. recent major 
reviews by Ruben and by Farlow et al.  Either conculsion is tenable, depending
on how you judge the conflicting interpretations of the evidence.  At least 
everyone agrees that dinosaurs were active, homeothermic, sophisticated animals,
and that complex social behaviour was not unusual.

On Wed 31 Jan 1996 Chip Pretzman wrote:

> 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.

Co-existence is NOT equivalent to competition.  Which mammal is a crocodile 
competing with?  I would have thought that two species with totally different
metabolisms and lifestyles would be more likely to avoid competition.

I am really unconvinced by arguments based on dominance and intra-specific 
competition.  I just don't understand what is meant by dominant mammals, because
by all quantifiable ecological parameters (biomass, energy flow, diversity etc)
mammals are insignificant (I mean compared to insects, nematodes etc).  
If you mean dominant at a particular size range or habitat niche you could 
define any group you might choose as dominant, but this is special pleading.
I don't think this is a useful concept.  Even comparing modern (non-avian) 
reptiles
to modern mammals you find that reptiles are more diverse and numerous.  Not 
that
I would bother, for the reasons given.

The fact that endothermy has arisen independently in so many groups suggests 
that 
there are no great evolutionary barriers preventing it, IF natural selection 
favours
it.  The fact that endothermic animals are a very small minority convinces me 
that
natural selection does not normally favour it.

> Really big dinos may have been
> functionally endothermic because of their big body size.

This sounds like ectothermic homeothermy; isn't that what you are arguing 
against?

> 
> 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.

Those who doubt that dinos were endothermic have never claimed that they would 
be
immobilised during the night; this is a parody of the position of Ruben, Farlow 
&
co. and suggests that you have not considered the ectothermic homeotherm 
arguments.
Sorry if I am wrong on that point - I really don't want to offend Chip or anyone
else, but contra-Bakker opinions seem to get some people very angry. 

Thanks for your time.

Tony Canning
tonyc@foe.co.uk