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Re: My apologies, but... physiology revisited



From: Nick Longrich <longrich@stardot.com>

 >    The fact is, insulation and RT do not appear in ectotherms as far
 > as we know. A certain minimum of insulation may be absolutely
 > necessary to endotherms (from size and fat if not from hair or
 > feather) with any kind of mammalian or avian-level physiology. RT is
 > a good idea if >99% of endotherms have it but obviously not necessary
 > if pelicans don't.

This is my other key objection to the Ruben et alii paper, one which
rereading the paper has not altered one whit.  Let's put this in an
aproximate contingency table format:

                 Presence of RT's
                 -       +
        Ecto-   100      0
        Endo-    99      1

[ In case anyone else is confused, I think Stan transposed the 99 and
  the 1 in the second row. -- MR ]

What can one actually derive from this?  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. That is it is *invalid*
to use the *absence* of RT's to conclude ectothermy.  The most
one can actually say is that the absence of RT's reduces the
*probability* od endothermy.

I find it interesting that Ruben et alii seem to have realized this,
and yet still try to make this very argument.  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.  Well, IMHO,
they *do* matter.

 > So if we find a feathered animal without RT we should be justified
 > in proposing it as an endotherm.

If there is evidence of a full body covering of feathers, yes.
If the feathers turn out to be limited to just a crest, then no.
[Note, the so far cited specimen of "Sinosauropteryx" is inconclusive
on this matter, as feather are *often* limited to the bedding plane,
so the animal may wel have had a full covering, we just can't tell].

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.