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My apologies, but... physiology revisited
I'm sure some don't want to see this subject again so soon, but my
frequent disappointment with the discussions here about dinosaurian
endothermy force me to say some things that are likely to be a bit
unpopular. I'm going to start by picking on Stan because IMHO he
should have known better than to have conspired in the following
"critique" of Ruben et al.'s 30Aug1996 _Science_ paper "The Metabolic
Status of Some Late Cretaceous Dinosaurs". In response to Jonathan
Melville Stan wrote (on December 19th):
I tend to agree with Dr. Paul here. A sample size of four is almost
always inadequate, for almost any purpose. The only time it is
acceptible, IMHO, is when there simply aren't any more samples
available. And there are certainly more species of birds available
I don't think Stan could possibly have read (or at least remembered)
the paper and still have written the above. I expect better of you
guys. I have the paper in front of me now, and I invite Stan to look
at its Figure 3. There are two regression lines here (much as you
might see in a discussion of Harry Jerison's "EQ"). There are 12
animals sampled form modern endotherms and 9 from modern ectotherms.
The regression lines (on a log-log plot) for the nasal cross-sectional
areas vs. mass are clearly distinct for the two groups. The study was
not based merely on "a sample size of four". Perhaps Jonathan's
defense makes a bit more sense now? Greg's "problems" with the
undersampling of the variability in nasal cross-sectional areas of
extant animals ought to explain why these areas fall on such nice
regression lines if there's no significance here. Since Greg claims
to have made relevant measurements I invite him to share his results.
More recently we were told (by Douglas Orr) that:
The generation of the majority of the body heat in endotherms is not
a result of aerobic metabolism (which also occurs in ectotherms) but
is, instead, a result of muscular contraction.
For an alternate view I'll quote Ruben's _Annual Review of Physiology_
paper from 1995:
It has long been recognized that about 70% of heat production at
rest in humans is generated by the internal organs (i.e. liver,
kidneys, brain, heart, intestines), even though they comprise only
about 8% of body mass (1).
1. Aschoff J, Gunther B, Kramer K. 1971. _Energiehaushalt und
Temperaturregulation_ Munich: Urban and Schwarzenberg.
It's true that skeletal muscle provides the majority of our heat
production during exercise, but it's not at all clear to me why said
heat is to be distinguished from "aerobic metabolism" since the
biggest difference between mammals and lizards in this regard is that
mammals are better at maintaining high activity levels while burning
the requisite energy aerobically.
I expect this to cause enough of a firestorm; I've held back up to now
mostly because I don't really have the time to get into a protracted
debate. I'll quit here in the hope of keeping subsequent messages
short as well. But before I go I'll add 1) that I'm about to forward
another message from Terry and 2) that my bottom line is only that
contrary to much of what passes through this list it still appears to
me there is no preponderance of evidence forcing any conclusion as to
whether or not dinosaurs were endothermic.
Mickey Rowe (email@example.com)