Re: erect posture and its implications

[ccp@okway.okstate.edu]

Dave wrote:
>I reiterate that terrestrial ectotherms walk at ectothermic speeds and 
terrestrial endotherms walk at endothermic speeds.  
     
{see my response to GS Paul; you have to consider body size in these 
comparisons}
     
>If a sauropod doesn't walk at <1 kph, why should we think it's an 
ectotherm?
     
{body size}
     
  And if it doesn't walk that slowly, WHY NOT?  
     
{body size}
     
>I reiterate that every correlation implies a causal link.  If one gives 
the matter a little serious consideration, rather than dismissing it out of 
hand (having had the mantra drilled into us by our professors as if it were 
some religious doctrine), one will realize that variables do not simply 
correlate out of thin air.  
     
{Well, this is way off topic, but let ME reiterate, in robotic, 
religious-dogma-like fashion, my serious-considerationless mantra that this 
is BS. Take 2 variables that we stipulate are NOT correlated (say, a 
geographical region's annual rainfall and the SAT scores of its inhabitants, 
or the number of mantra-drilling professors at a university and the age of 
menarche of its coeds, or whatever). If I take 100 samples of these two 
uncorrelated varibles, on average 5 of the samples will have a correlation 
coefficient that is statistically significant (by the conventional P<.05 
criterion). If I take just one sample, there is a 5% chance that I will 
conclude the variables are correlated een though the omniscient observer 
knows they really are not.}
     
>These hypothetical variables that correlate yet have nothing to do with 
each other simply do not exist in reality.  If
anyone can cite me just one example I will be only too happy to eat my words.
     
{There is a classic book that I have not seen in years called _How to Lie with 
Statistics_ which as I remember contains actual examples of many such absolutely
spurious correlations. I seem to remember the example of sunspot activity and 
Dow-Jones average.}
     
>It may be that a fully erect posture, an endothermic metabolic rate, a 
high-surface area respiratory system, a high performance cardiovascular 
system, and physiological temperature regulation all tend to evolve 
simultaneously in response to selection for increased aerobic capacity.  A 
partially erect posture and 4-chambered heart may preadapt an animal for 
this.
     
{This correlated evolution scenario seems more likely to me than the causal 
"forcing" thing.} 
     
I should point out that of course dinosaurs would have demonstrated some 
degree of variation within the endothermic theme.  As with living 
endotherms, metabolic rate probably varied as a function of diet and other 
factors.  Some species may have had tenrec-like temperature regulation 
while resting at warm temperatures.  The presence of growth rings in some 
dinosaur bone suggests that some species may have had winter torpor states 
or even an ectothermic type of metabolic response below certain 
temperatures.  All of this is nevertheless within the overarching theme of 
endothermy, just as the ability of pythons to elevate their temperature 
above ambient for months at a time is within the theme of ectothermy.  
     
{Well, I have to pick a nit here: brooding pythons are by definition 
endothermic (while brooding), not ectothermic. If your point is that ecto 
vs. endo is a false dichotomy with lots of exceptions and intermediates, I 
wholeheartedly agree. Yet you guys really seem to work hard to make 
everything consistent with your preconceived "overarching theme of 
endothermy." The evidence is, in fact, very equivocal, and any truly 
objective jury is still out. Some of the evidence against true endothermic 
homeothermy is very strong. I still like the title of Benton's(? can't find 
my copy) paper on sauropods: "The improbable endotherm." Dinosaurs were 
diverse, their metabolic strategies were probably diverse, and big sauropods 
are among the LEAST likely groups to have had elevated metabolic rates. But 
of course its fun to speculate and argue about it.}
     
>The question remains why is there this tremendous gap in metabolic rates 
between extant endotherms and ectotherms, and why birds and mammals have such 
similar rates.
     
     {Both questions are likely related to 1) endothermic temperature 
     regulation in birds and mammals but not ectotherms, 2) the universal 
     advantages of maintaining a relatively high body temperature if 
     temperature can be regulated, and 3) the similar thermal conductances 
     of birds and mammals of similar body size due to the use of unstirred 
     air layers (trapped in fur or feathers) for insulation and the 
     consequent metabolic rates necessary to replace heat lost at similar 
     rates.}