[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: My apologies, but... physiology revisited

I feel like I've succeeded with my main goal of rattling cages,
getting people to recognize that the metabolic status of dinosaurs
isn't really known, and most of all getting people to be more fair in
their analyses of ideas which run contrary to their own.  So after this
message I'm going to take Jonathan's advice and take five on the
subject.  I'll let Stan have the last word when he finishes his
literature search.  

Most of Stan's objections to the OSU crowd's work have already been
addressed *here*.  I won't go through those again.  There is one major
one, however, that hasn't quite been dissected.

Stan wrote:

> One can conclude that RT's imply endothermy.  That is, the
> *presence* of RT's is good evidence *for* endotermy.  However, the
> converse *cannot* be derived conclusively from this data.

Using Stan's reasoning it would be impossible to show that *any* trait
is necessary for endothermy.  That's life.  That was, in fact, the
point of my objection when I differentiated science and math.  It is
not possible to demonstrate the necessity of any particular adaptation
for any particular method of doing something (in this case RT's for
conserving respiratory water) because as a rule biological organisms
defy such generalization.  However, in the fully fleshed-out theory
of dinosaur endothermy (a la Nick's earlier message) it must be shown
that either a) RT's aren't as important as the OSU crowd claims they
are with respect to retaining respiratory water and heat losses, or b)
dinosaurs must be shown to have some other mechanism for compensating
for respiratory water and heat losses.

On that note:

> In one long footnote they refer to at least two exceptions to
> endotherms having RT's, and then try to explain why they do not
> really matter.

Stan is lapsing into unfairness again.  The authors do not claim that
the exceptions don't matter.  They say that the exceptions can be
accounted for because they appear to have other mechanisms for
retaining (whales) or compensating for the loss of (Pelecaniformes)
respiratory water.  To show you that Stan is being unfair, I quote a
sentence (from that footnote) which I invite you to compare with
Stan's appraisal:

  However, in these exceptions, the presence of compensatory
  mechanisms serves to emphasize that endothermic lung ventilation
  rates necessitate some adaptation in order to counteract loss of
  respiratory water or heat[.]

Contra Stan's analysis they say that these exceptions *are* important
because they provide support for the contention that respiratory water
and heat loss are major problems for endotherms to contend with.  In
order to make these exceptions relevant to dinosaurs, someone would
have to show that either a) dinosaurs had a specialized nasal
compression mechanism (unlikely since there's no evidence that
dinosaurs were diving animals) or b) they had some form of salt
excretion mechanism so that they could drink sea water (again unlikely
since dinosaurs don't seem to have spent a lot of time in the ocean).

Other compensatory mechanisms are possible, of course.  You could
argue that the air was much more humid where dinosaurs lived (unlikely
since a) I think geologists and palynologists could easily dispute the
claim and b) contemporaneous mammals have been shown to have RT's).
You could argue that dinosaurs developed irrigation systems so that
they could constantly drink to replenish the water they were breathing
out.  You could argue that they developed stillsuits like those used
in "Dune"...  Ok, ok, now I'm not being completely fair -- I'm opting
for humor.  But the point stands that a good case has been made that
respiratory water loss is an important problem for endotherms, and if
dinosaurs were endotherms then they must have found a way around the
problem.  At present there is no evidence that they did.

All that said, it should be stated that there is no call here for a
return to the view of dinosaurs as sluggish creatures (Ruben has
explicitly disavowed such a contention).  There's nothing "uncool"
about not generating your own heat internally.  In fact, we're rather
wasteful about producing heat.  I suspect not many of you know that
our cell membranes are more permeant to ions than are the cell
membranes of ectotherms.  Consequently we waste a lot of energy
pumping ions around in order to maintain the appropriate
concentrations in the appropriate places.  Personally I think that's
kind of uncool...

If I approve it, this should be the last message to go through a
moderated dinosaur list.  May the force be with us.

Mickey Rowe     (mrowe@indiana.edu)