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Re: pubic boots and hepatic piston lungs

John R. Hutchinson writes;

>        Birds, on the other hand, developed their air sacs (esp. the large
>posterior sac) late in their evolution, as evidenced by the uncinate
>processes, enlarged sternum, and loss of gastralia (in Ornithothoraces?
>sorry, no papers handy, but at least excluding Enantiornithes according to
>Ruben) that other theropods lack. Those features are apparently correlated
>with the flexibility of the ribcage / expansion of the air sacs.

As long as we are on the subject, what are the latest theories about how/why 
air sacks evolved?

This can of worms opened by...

Rob Meyerson
Orphan Vertebrate Paleontologist

The most exciting phrase to hear in science, the one that heralds new 
discoveries, is not "Eureka!" (I found it!) but "That's 
funny ..." 
-- Isaac Asimov