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Re: [GSP1954@aol.com: MORE DINOSAUR ENERGETICS]



Van and Kathy Smith wrote:

> Perhaps the fact that, as a rule, mammals have highly developed
> olfactory equipment, the larger nostril size was developed in many
> of them to enhance this sense. ...

First off, let me say that I agree with you and Mr. Paul.  However, I 
see a chicken and the egg argument here.  It is also just as likely that 
the highly developed olfactory equipment evolved because the supposed 
need of endothermy for wider nasal passages preadapted them for it.  In 
other words, they could have already had the large nostril size which 
then allowed them to develop enhanced olfactory equipment.  And to throw 
out a wildly speculative fancy here, the small nasal passages of the 
ectotherms could have inhibited olfactory evolution and promoted the 
evolution of the Jacobson's organ providing them a quite sufficient 
analog of the mammalian olfactory system.

One other thing, perhaps someone else has mentioned this before but not 
sufficiently it seems.  People talk as if animals are either full blown 
mammalian endothermic or they are amphibian ectothermic.  Endothermy 
like everything else had to evolve.  It did not suddenly appear in all 
its glory with the arrival of a new species from a fully ectothermic 
animal.  To answer most of the critics on both sides of the fence, 
especially the turbinate problem, it seems to me that the most likely 
situation we have is that the dinosaurs were clearly endothermic but 
likely not at the level of modern mammals or at least certainly not 
using all the same methods.  Endothermic aniamls evolved improvements on 
the system as they went along.  This may explain why the avians do not 
supposedly show any sign of the turbinates until, what was it, 70 
million years ago even though  they clearly had endothermic markers well 
before then?  Avians clearly have a superior respiratory system than 
mammals which was likely inherited from the dinosaurs, they possibly did 
not need the turbinates as quickly in the development of their 
particular style of endothermy as mammals did.
Which brings to mind the question, why is the size of the nasal passages 
all that important anyway?  It seems to me that what is important is the 
ability to extract oxygen from the available air and eliminate the waste 
gases.  The avian system is far better at this than the mammalian system 
which is rather wasteful in this regard.  I don't know if anyone has 
thought about this but mammals don't absorb most of the oxygen they 
breathe in, avians if I remember correctly absorb a much higher 
percentage.  This has been attributed to the need for keeping the flight 
muscles oxygenated.  I consider this to be a rather flimsy 
rationalization and I think works far better as a inheritance from the 
dinos.  Anyway, this sort of throws a wrench in the whole size of the 
nasal passage discussion to me.

Joe Daniel