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Re: _Discover_ article



On Nov. 25, Steven Faust wrote:

>Reptilian physiology would not have precluded the level of activity
>depicted in "Jurassic Park".  The only inaccuracy in the film: dinobreath
>would not have misted refrigerator glass.

        As I have stated in a previous posting, the "ectotherms can't
produce steam" idea is incorrect.  Reptiles are fully capable of producing
exhaled air which is below body temperature (and above ambient temperature),
so, regardless of their physiologic status, the _Jurassic Park_ 
velociraptors could have misted refrigerator glass.
        As for the rest of the _Discover_ piece, Tomasz Owerkowicz's work
on bone microstructure in relation to exercise-induced bone strain is
interesting, but not new.  It has been known for some time that application
of increased mechanical strain to bone results in an accelerated rate of
secondary osteonal remodelling.  It has also been known for some time that
growth rates of endotherms and ectotherms overlap.
        In regards to respiratory turbinates (RT), the hypothesis that RT
evolved to reduce rates of respiratory water loss because of high ventilation
rates in endotherms sounds logical on the surface.  However, there is no 
direct experimental evidence which demonstrates that the nasal cavity 
actively regulates water loss.  A reduced exhaled air temperature 
certainly conserves water, but it also conserves heat, and it could be that
a reduction in respiratory water loss represents an entirely passive and
unavoidable consequence of active heat conservation (Hill, 1978).  
Lizards can conserve respiratory water, even though they lack RT, as do 
whales, who exhibit extremely low rates of respiratory water loss
(Kasting et al 1989). For example, if the nasal cavity actively controlled
water loss, one would expect that heat-stressed, dehydrated mammals would
have reduced respiratory water loss relative to hydrated ones, yet this 
does not appear to be the case (Schroter et al 1987).

REFERENCES
        Murrish, D.E., & Schmidt-Nielsen, K. (1970).  Exhaled air temperature
and water conservation in lizards.  Respiration Physiology, 10, 151-158.
        Hill, R.W. (1978).  Exhalent air temperatures in the virginia
opossum.  Journal of Thermal Biology, 3, 219-221.
        Schroter, R.C., Robertshaw, D., Baker, M.A., Shoemaker, V.H.,
Holmes, R., & Schmidt-Nielsen, K. (1987).  Respiration in heat-stressed
camels.  Respiration Physiology, 70, 97-112.
        Kasting, N.M., Adderley, S.A.L., Safford, T., & Hewlett, K.G.
(1989).  Thermoregulation in beluga (_Delphinapterus leucas_) and
killer (_Orcinus orca_) whales. Physiological Zoology, 62 (3), 687-701.
        Bouvier, M., & Hylander, W.L. (1981).  Effect of bone strain on
cortical bone structure in macaques (_Macaca mulatta_).  Journal of 
Morphology, 167, 1-12.
        Rubin, C.T., & Lanyon, L.E. (1984).  Regulation of bone formation 
by applied dynamic loads.  Journal of Bone and Joint Surgery, 66, 397-402.
        Wolkomer, R., & Wolkomer, J. (1996).  Alligator serenade.  Wildlife
Conservation, 99 (1), 22-29.
        Case, T.J. (1978).  On the evolution and adaptive significance of
postnatal growth rates in the terrestrial vertebrates.  Quarterly Review
of Biology, 53, 243-282.
        Buffenstein, R., & Louw, G. (1982).  Temperature effects on 
bioenergetics of growth, assimilation efficiency and thyroid activity in 
juvenile varanid lizards.  Journal of Thermal Biology, 7, 197-200.

Guy Leahy
Dept. of PEHR
Western Washington University
Bellingham, WA 98225
n9435712@henson.cc.wwu.edu