Re: New refs (short)

["Tim Williams" <twilliams_alpha@hotmail.com>]

DinoBoyGraphics@aol.com wrote:

>      Monotremes and marsupials show a whole suite of morphological and 
> reproductive variety beyond placentals, so by any morphological standard, 
> they would better approximate the diversity seen within archosauria (or 
> maybe ornithodira, if such a clade exists), which does indeed show a wider 
> range of RMR strategies.

Sorry, but your comparison is still artificial.  It's also circular (just 
read the above paragraph and you'll see why).

And you haven't explained why the Archosauria can (and did) evolve different 
metabolic strategies, whereas a subset of this group (the Dinosauria) could 
not.  Why couldn't they?

There is evidence that the agile, upright ancestors of crocodylians were 
endotherms.  If endothermic sphenosuchians could give rise to ectothermic 
crocs, why couldn't there be metabolic changeovers within (say) the 
ornithopod or theropod lineages?  Your argument is "Because placentals all 
have the same RMR."  My reply is "So what?"



Tim

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