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Re: New refs (long)



<Are you kidding???!!!>

I never write 3 page emails just to kid ;)

<I'll list just a few "extant animal groups" that display a range of 
metabolisms:
Mammals: <snip> Sharks: <snip> Fishes: <snip> Insects: <Snip>>

      Ok, this is a much better line of evidence than claiming that big mammals 
(all of which are placentals today) are less endothermic than small mammals.  
Itâs inconsistent, though, to use so many marine organisms as your examples 
of metabolic diversity, but then argue, âno extant land mammal has ever 
achieved the dimensions of the largest sauropods - or even the largest 
hadrosaurs.â  

<All your math pertains to placental mammals.  You're assuming (very bravely) 
that Placentalia constitute a satisfactory analog for the Dinosauria.  
However, no extant land mammal has ever achieved the dimensions of the 
largest sauropods - or even the largest hadrosaurs.  Your choice of the 
placental clade of mammals for comparison is a Strawman.>

     Ok, let me get this straightâarthropods and lamniforms are good dinosaur 
analogs, but placental mammals are a strawman?!  I think your comparative morph 
maybe a bit rusty.  To begin, the math applied to all terrestrial 
tetrapodsâthe constant of 70 kcal, in 70 kcal / kg^.75 applies as a general 
rule to placental mammals.  No extant land mammal gets close to the largest 
sauropods, but extinct indricotheres get as large as many sauropods, and are 
larger than any known hadrosaurs skeleton (I understand there is ichnological 
data suggestive of larger hadrosaurs).  Do you suggest that indricotheres were 
ectothermic?  For that matter, how about probiscideans, since most 
non-sauropods donât get larger than big bull _Loxidonta_?

<Placental mammals represent a very limited (and very artificial) clade for 
comparison to dinosaurs.  Would you say that _Coelophysis_ and  _Brachiosaurus_ 
had the same metabolism as any modern bird?  If you don't, then you're argument 
is already dead in the water.  If you do, then you're on your own...>

     Iâm really not sure what you mean by placental mammals being an 
artificial clade.  As in not monophyletic?  Iâm sure I could find a few 
mammals paleontologists who would take issue with that.  Surely you arenât 
referring to the amount of morphological diversity?  It far exceeds that of 
dinosaurs.  There are no brachiating dinosaurs, no cetacean analogs, no sea 
otter analogs.  Even ignoring pinnipeds, Carnivora has far more diversity in 
its lineage than theropods (exclusive of aves).  There is far more variety in 
niche exploitation and locomotive style in placentals than in dinosaurs.  
     Youâre right, of course, that inclusion of marsupials and monotremes 
greatly expands the range of metabolic adaptation seen in Mammalia, but then 
you are including groups with three different reproductive styles, for crying 
out loud!  I would be very interested indeed in arguments that claim that 
dinosaurs are more diverse than the âartificialâ group of placental 
mammals.  Or why arthropods or chondrithyans are better models.
     As for your final question, âWould you say that _Coelophysis_ and  
_Brachiosaurus_ had the same metabolism as any modern bird?â  Yes.  A kiwi 
has a RMR of 40 kcal / kg^.75.  Much higher than the 5-15 kcal range of extant 
reptiles, much lower than the 70 of mammals.  Based on the growth style in 
sauropods and early theropods, which exceeds that of âgigantothermicâ 
Deinosuchus, it seems reasonable to suppose that both genera have RMRs at least 
that high (especially in light of data that shows sauropod juveniles growing 
faster than other dinosaursâdonât anyone say itâs because they have to 
grow more to attain large size, thatâs not what Deinosuchus does!).

<The fact that some dinosaurs were feathered and (as far we can tell) all 
dinosaurs were not is positive evidence for metabolic variation within the 
Dinosauria.>

Like the fact that some placentals were furry and others (most assuredly) are 
not proves that some placentals had a reptilian RMR?  This line of reasoning 
may prove telling; one can compensate with fat deposits and behavioral 
regulation, but if we find a few unfeathered hypsys, etc, I would admit that it 
is evidence in favor of your supposition, though not conclusive.

Scott