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Re: [GSP1954@aol.com: MORE DINOSAUR ENERGETICS]



I know some of you may be tired of this, but I felt compelled to respond to
Greg's comments...

If an animal has high metabolism (high O2 consumption) and therefore high
lung ventilation rates, the nasal passage proper must be large enough to
accomodate increased airflow.   In order to house the RTs (which as has been
pointed out many times, >99% of endotherms possess), without increasing
resistance to airflow, the nasal passage of endotherms must be larger still.
For the same reason ectotherms have narrower nasal passages since they have
lower metabolism and correspondingly low lung ventilation rates.  This is
not a result of our work, but it is a law of physics (Poiseuille's law:
flow rate is proportional to radius^4  -- in other words,  decreasing the
radius of a tube by 1/2 increases the resistance to flow 16x).   Regardless
of how many specimens you observe (our data set may not have been large, but
they were significant--these two terms are not synonoumous--it is possible
to have a large, insignificant data set if the methhodology is not sound),
this law still governs the size of the nasal passage--you can't have an
endotherm with a narrow nasal passage (relative to body mass).  It may
appear that some endotherms have relativeley narrow air passages (or that
some ectotherms have large air passages), but when compared with body mass,
the relationship holds true--there is an approximately 4-fold gap between
the nasal x.s. area of modern endo- and ectotherms when compared to body
mass.  I'm waiting eagerly for the results of Greg's work to come out in
print...I hope there is an explanation included for the apparent
contradiction of Poiseuille's law.

As I said before, the features (e.g., erect limb posture) presented by Greg
as "evidence" of endothermy in dinosaurs are not causally or functionally
linked to metabolic rate.  There are and have been animals with erect limb
posture that aren't or weren't (as far as we know) endotherms.  Also,
crocodilians have semi-erect limb posture but their metabolic rate is the
same as other modern ectotherms.  If posture is causally linked to
metabolism you would expect crocs to have "intermediate" metabolic rates.
Moreover,  some mammals don't have erect limb posture but are still
endotherms.  

By the way, the three dinosaurs we used were the only three available.
There was no horned dinosaurs that are preserved 3-dimensionally and not
significantly altered by preparation.  Maybe Greg has access to specimens we
don't know of...

Recently a student asked me "why is it so important to some people to have
dinosaurs be 'warm-blooded'?"  I couldn't answer the question, maybe someone
can help...
Personally, I don't see why it matters.  Dinosaurs are important
biologically regardless of their metabolic rate.  This doesn't seem to be
the opinion of the majority.  The classic interpretation was that dinos were
slow, sluggish, stupid creatures doomed to extinction because of their
"backward" physiology.  In the last 20 or so years there has been a serious
effort to show that they were not this way instead they must have been like
mammals and birds--how else could they have been so successful.  The problem
is that neither of these may be correct.  It is entirely likely, regardless
of what Greg Paul thinks, that dinosaurs, et al. were not mammal- or
bird-like in their physiology.  However this doesn't mean that the "classic"
interpretation was right.  Ectothermy does not = slow, stupid and doomed as
any one who has seen a hunting Komodo dragon will attest.  Given the
probable equitable climate of the time, dinosaurs probably has the best of
both worlds--the relatively constant body temp of an endotherm (helped out
by the size of many of them) and the less expensive lower metabolic rate of
an ectotherm.  For many of these creatures their daily life was probably
more active than modern lions.

[ Note that Terry's not subscribed, so he didn't see Greg's message
  about the komodo dragon.  -- MR ]

TDJ
:-{)
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    Terry D. Jones                             Voice:  541/737-6120       |
    Oregon State University              Fax:      541/737-0501          
    Dept. of Zoology                         JONEST@bcc.orst.edu
    3029 Cordley Hall
    Corvallis, OR  97331-2914
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