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respiratory turbinates revisited
Recently we've had considerable discussion of the significance of the
presence or absence of respiratory turbinates relative to
thermoregulation. For an unrelated matter, I was glancing through
Alexander's _Dynamics of Dinosaurs and Other Extinct Giants_ the other
day and came across this comment (p. 104) that I don't recall being
discussed here previously:
"If dinosaurs had fast, mammal-like metabolism . . . the largest would
have been liable to overheat unless they lost a lot of water by
evaporation from their skin and in their breath."
In their recent article in _Science_, Horner and colleagues (I don't have
the citation and author list handy) concluded that since the dinosaurs
they studied lacked respiratory turbinates for reclaiming bodily moisture
they would otherwise lose due to their high-volume respiratory
ventilation rate, they could not have had the high-volume ventilation
that is necessary for endothermic metabolism.
However, Alexander, referring to the well-known problem of very large
endothermic dinosaurs being in danger of cooking in their own juices, is
saying that dinosaurs (at least the very large ones) might lack
respiratory turbinates because with enough evaporation of moisture into
the respiratory air stream, they might be able to keep themselves cool.
The last thing they would have wanted to do would be to try to reclaim
that moisture, thus putting all of that heat right back into their
The significance of this thought is that not only might the absence of
respiratory turbinates NOT disqualify an animal from being an endotherm,
but it would also show that it is at least possible for dinosaurs to have
used unique mechanisms to control excessive heat buildup in their bodies,
allowing the very largest ones to have been just as endothermic as
smaller ones (which some people have claimed is very unlikely or even
impossible). Perhaps they simply drank a lot of water, specifically so
it could evaporate into their breath.
For those of us who prefer the view that most or all dinosaurs were
endothermic at least to a degree, might this, perhaps, kill two birds
(i.e., objections to our view) with one stone? I know the obvious retort
is that Horner et Al had observed that the small and medium-size
dinosaurs they studied also lacked turbinates, but I have in mind a
larger view of this. For example, do we really know enough about the
physiology of dinosaurs to know whether or not they MUST have had
respiratory turbinates to have been endothermic? Comments?
Norman R. King tel: (812) 464-1794
Department of Geosciences fax: (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712 e-mail: email@example.com