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Re: responses to pterosaur discussion



At 11:54 AM 07/02/01 -0600, Demetrios M. Vital wrote:
So if we cannot establish certain differences between groups, such as the hemoglobin efficiency, then all we have left to compare is the gross physical structure.  And if guesses are the best we can deal with, why shouldn't we deal with those educated guesses?

Because they may not be educated.  Listen, speculation is dandy, but if you are proposing a serious hypothesis it can't be built on a pile of "ifs".  In this case, the margin for error you would get in comparing respiratory efficiency between birds and pterosaurs without physiological information may well be so great that you could never clearly answer even the simple question as to whether their respiratory efficiencies were alike or different.  Can you tell me, for example, the tidal volume in pterosaur lungs?  The degree of vascularization?  The oxygen-binding ability of pterosaur hemoglobin?

We are finding in living turtles that there are many different hemoglobins with different oxygen-binding abilities, and an individual species may have as many as six.  Thus the range of physiological variation has the potential to be far greater than the physical structure of a turtle skeleton could possibly indicate.  The same may well be true for other taxa.

Besides, it is one thing to speculate on how pterosaurs breathed (and a perfectly valid thing too, especially if you could figure out a way to test your hypothesis).  It is another thing to get into a second level of speculation in which you propose to explain pterosaur extinction by a physiological mechanism you cannot prove existed.  This is piling speculation on speculation.  It may be fun, but it is hardly useful science.

Yes, it would take an in-depth study to guage the exact differences between taxa, but would you go into a study or discussion assuming all taxa have the same respiratory abilities?

Of course not - precisely my point.  But would you go into a study assuming that the physiological aspects of respiration, which you cannot measure in pterosaurs (or in Mesozoic birds, for that matter), were so much alike in birds and pterosaurs that a difference in physical respiratory structure would translate directly into a difference in respiratory efficiency?

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