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Re: CNN on Lungs and Feathers



Stan Friesen wrote:

>I see a possibility for even a different system.  If the postero-ventral
>air sacs were relatively small, could they not be inflated by a diaphragm?
>(Provided they remained anterior to it, that is).

Si!  What I've been groping toward is the thought that the whole thing may
have developed anteriorly, perhaps even as the *result* of a hepatic piston.
We can be modestly confident that anterior air sacs of some sort were
present in numerous Theropods and proto-dinosaurs.   Assuming Ruben is
correct, and further assuming that a hepatic piston was relatively common at
least among smaller critters, this would give us a means of driving an air
sac system.  At some point, of course, the piston -- and the need for an
airtight septum -- might become superfluous.

>>Pterosaurs managed it without endothermy.
>
>I am not sure we can really say that for certain.

Agreed.

  --Toby White