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Re: Function Talks at Ostrom Symposium

In a message dated 2/20/99 1:42:24 PM EST, EctoDino@aol.com writes:

<< 2) What Ruben et al. meant is since birds are not diaphragm breathers a
 diaphragm breathing ancestor for birds would have to rupture its diaphragm to
 gradually eliminate it and breath without one. However, you try breathing
 a ruptured diaphragm! Such a debilitating condition would immediately
 compromise the entire pulmonary ventilatory apparatus and seems unlikely to
 have been of any selective advantage.

Birds therefore must have developed their present lung system >alongside<
their original diaphragmatic lung system, at first simply to increase
ventilatory efficiency as they became better fliers. Gradually the original
system was lost (or became modified into, say, part or all of their air sac
system--to figure out the details requires examination of extant-bird
entrails) as the newer system took over more of the respiratory function. This
didn't happen overnight, and I look forward to the discovery of possible
flightless, very birdlike theropods with well-preserved innards showing signs
of >both< kinds of respiratory systems--say in Brazil.