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Re: New refs (short)
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?"
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