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RE: Function Talks at Ostrom Symposium

On Saturday, February 20, 1999 12:33 AM, Stewart, Dwight 
[SMTP:Dwight.Stewart@VLSI.com] wrote:


>          How certain is it that dinosaurs WERE diaphragm breathers?  And
> why would the transition
>       forms (IF dinosaurs were diaphragm breathers) be selected for a
> diaphragmatic hernia?
>       Dwight

1) Not too certain yet.   Unfortunately, soft tissue remains are all we really 
have for diagnosis, and this type of fossil is of course very rare.  Ruben's 
recent reanalysis of Scipionyx is a good study, IMHO, but not conclusive by any 
means.  You have to buy some plausible, but not 100% certain, assumptions.

2) Avian respiration requires air sacs connected to the lung, but posterior to 
the diaphragm.  Ruben's point is that you have to make holes in the diaphragm 
to do this.  Since croc-style respiration depends on creating pressure 
differences between the anterior and posterior compartments (i.e. across the 
diaphragm), placing any part of the respiratory system posterior to the 
diaphragm would cause the whole system to collapse.

  --Toby White