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Re: Turbinates and welcome Mark Sumner



On Mon, 4 Mar 1996, Roger A. Stephenson wrote:

> I was under the impression, maybe ignorantly, that turbinate structures
> were involved in the sense of smell and in controling water loss. If this
> is the case then the absence of such structures in larger tyrannosaurids
> might suggest a lowered danger of dehydration 'cause of the greater body
> mass. If that was the case how do these structures relate to the sense of
> smell? I thought T-rex could smell very well.

In reading up on turbinates, one of the first things I discovered
was that there are actually TWO DIFFERENT kinds of turbinate
structures:  respiratory and olfactory.  Respiratory turbinates
are the ones that I had been asking about, the ones that Paul
Ruben considers a criterion for endothermy.  These are the ones
that prevent the loss of heat and moisture during exhalation.
These are also the ones that Gregory Paul was saying are
cartilagenous in birds and so might leave no trace whatsoever
in a fossil.  The OTHER kind of turbinate, olfactory turbinates,
are the ones that were found in Nanotyrannus (see Bob Bakker
article in _Discovery_, um, I'll get the date for you in a little
while!!).  These are "trumpets" of bone within the skull that
have olfactory tissue attached to them in the living animal,
and are directly related to the sense of smell.

So...The PRESENCE of olfactory turbinates in the the skull
of an animal doesn't necessarily say anything about whether it
is warm-/cold-blooded, and the ABSENCE of respiratory turbinates
(which may leave no trace in fossils!!) doesn't necessarily
say anything about the animal's sense of smell.  This distinction
between olfactory and respiratory turbinates and their unique
properties is an important one.

Also, I believe the reason T rex. supposedly had a good sense
of smell has to do with the size of the braincase area that
would have contained the olfactory bulb.  I haven't heard
anything about olfactory turbinates yet in T rex.

I hope this helps a little bit, somebody please correct me
if I'm mistaken about anything!

Thomas Duffy
thomasd@clark.edu