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Re: Lungs and Feathers



> It cannot be overemphasized that
>kiwis simply do not have sternal plates long enough to operate the posterior
>air-sacs, only the ribs can operate them.

How do you propose this happens?  Rib movements in modern birds is in the
fore-aft direction (as noted in the references you cite).  Using ribs
without the sternum cannot ventilate air sacs since there would be little,
if any, change in intraabominal pressure.  If  I'm not mistaken, you pointed
out that the abdominal air sacs in kiwis were reduced, if this is the case,
an elongate sternum is not necessary in these birds.

>Am I suggesting sauropods had a bird-like air-sac complex? You bet, and so
>have others. Of course the intensely pneumatic vertebrae confirm the presence
>of air-sacs. The ribcage, especially the rib-head/vertebral articulations, is
>remarkably bird-like. The long mobile abdominal ribs could ventilate the
>posterior air-sacs. This very efficient respiratory system probably evolved
>in order to overcome the dead space inherent to their very long trachea. 

Speculation aside, pneumatized and/or excavated vertebrae indicate
attachment of the lung to the dorsal body wall.  In modern birds and
numerous modern reptiles the lung is attached to the dorsal body wall.
Pneumatization of the vertebrae alone merely demonstrates that there were
diverticula from the lung proper.  Lung diverticula are common among modern
reptiles (e.g, in rattle snakes nonvascular lung diverticulae extend nearly
to the cloaca).  Furthermore, it is unclear as to the mobility of the
gastralia (I assume that Leon Claessens is still looking at this question).
Regardless, it is doubtful that movements of the gastralia would result in
significant changes in intraabominal pressure to allow filling and/or
emptying of abdominal air sacs.

>

>
>GSPaul
>
TDJ
:-{)>
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    Terry D. Jones                             Voice:  541/737-6120     
    Oregon State University              Fax:      541/737-0501          
    Dept. of Zoology                         JONEST@bcc.orst.edu
    3029 Cordley Hall
    Corvallis, OR  97331-2914
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