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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