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Re: New refs (long)



<Are you seriously arguing that *every* dinosaur - from herrerasaurs to 
brachiosaurs to iguanodonts to microraptors to 
hummingbirds - adhere(d) to the same metabolism?>

     No, I'm saying that none of them had a RMR constant less than 30-40 kcal 
(/ kg^.75), which is twice that of modern reptiles.  

<I never argued that arthropods and lamniforms and good dinosaur analogs.  My 
point was to refute your statement: "There is absolutely no support for this 
[i.e. variability in endothermy/ectothermy] amongst extant animal groups.">

     Ok...there is "support" for alien abductions (I've seen books full of it), 
but it isn't _good_ support.  I'll discuss comparative analysis below in 
reference to other statements.

<I mean your choice of the clade Placentalia as analogs to the Dinosauria is 
artificial.  You nominate a clade (Placentalia) where the constituent taxa stay 
within fairly narrow metabolic confines, and then argue that because placentals 
do, then dinosaurs must have as well.>

     Ok, the argument by analysis was introduced by the original paper 
comparing croc metabolics to dinosaurs.  I'd prefer to just look at the 
empirical data (e.g. growth data).  They claimed that there was diversity in 
croc thermal strategies stratified by size, but actually crocs maintain the 
same RMR constant, so they are NOT varying their metabolic adaptation, though 
they are varying their thermal regulatory strategy (taking advantage of size).  
Extant crocs are less morphologically diverse than either extant placentals or 
birds, and low and behold, they show almost no variation in RMR constant at 
all.  Despite a fairly large range of RMR rates in birds and placentals, none 
of them exhibit RMRs in the squamate range.  More importantly, there is little 
or no correlation of RMR with size in birds, and none in terrestrial mammals at 
all.  In fact, name any group in which the RMR constant scales inversely with 
size.
     I did not pick placentals because of their narrow metabolic range, but 
because of their morphological range.  I restricted my choices to terrestrial 
tetrapods because the energetics of marine organisms and arthropods make them 
invalid comparisons.  You could use extant squamate; they also demonstrate a 
correlation between variety in morphological adaptations (less than placentals) 
and variety in RMR strategy (surprise, less than placentals!).
     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.
     I read HP Holtz's excellent post on "no rules of higher taxa comparison," 
which is completely true.  It's also mute, because I wasn't comparing them 
based on phylogenetic "rank" (for those who still use ranking) but rather on 
actual biological features.

<Now you're trying to do something very tricky: measure 'morphological 
diversity', and use it to justify comparing one clade to another.  See above.>

     Look, if you want to use comparative analysis, you have to base it on 
something.  You can't pick a group based on the trait in interest (that is, you 
can't pick Mammalia just because they have a large range of metabolic 
strategies), you have to correlate your variable with something else.  Don't 
like morphology?  Then you pick an index.  There are only two options here; 
pick some index that supports your supposition that it is normal for there to 
be a high degree of endothermy-ectothermy crossover in a dinosaur-like clade, 
or give up on trying to use comparative analysis as evidence.

    Just to be clear, I donât believe that placental metabolic variability 
proves that dinosaurs were all warm-blooded, just that the lack of similar 
comparative group falsifies the widespread myth that there is good evidence to 
support it from comparative analyses to extant tetrapods (i.e. relevant 
comparative groups).


<I think the world would be a much better place if people could move away from 
the "endothermy vs. ectothermy" and "warm-blooded vs. cold-blooded" 
dichotomies.>

     Hereâs where we totally agree.  For example, if people stopped 
associating endothermy with âwarm-bloodedness,â they would understand that 
mass homeothermy has little or nothing to do with explaining dinosaur 
histological data.  The spread of Mammalian RMR and AEC strategies, which 
nearly bridges the gap to extant reptiles, would probably give us a good data 
set to start examining what level of RMR is required to supply the growth rates 
that dinosaurs had, but that giant âhomeothermicâ crocs do not.  Also, a 
better grasp of metabolics would lay to rest the myth that RMR constants EVER 
scale with mass. Sure, ostriches and rheas have lower RMR constants than 
songbirds, but they have higher ones than kiwis.  Big crocs do not have lower 
RMR constants than little crocs, and probiscideans and rhinocerotids do not 
differ significantly from the mammal average, and are higher than smaller 
monotremes, marsupials, etc.  There is no empirical evidence for the fallacious 
as!
sumption that big terrestrial tetapods have lower RMR constants than smaller 
relatives (note that Iâm not talking about mass-specific metabolic rates, 
which always are lower in bigger animals than smaller animals of similar 
metabolic strategy).

Scott