respiratory turbinates revisited

["King, Norm" <nking.ucs@smtp.usi.edu>]

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 
bodies.

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?


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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:  nking.ucs@smtp.usi.edu