Re: Belly Ribs and Breathing

[Waylon Rowley <whte_rbt_obj@yahoo.com>]

> >I'm wondering if "holding in the visceral mass" is
> a good argument.  If
> >that was their primary function and Ornithischians
> did not possess them,
> >how did Ornithischians hold their innards in?


Ok, time for rampant hypothesizing. What if gastralia
are not preserved in (most) ornithischia because they
lack an avian respiratory system driven by the
contraction/expansion of the air sacs? So, in
non-avian theropods the abdominal air sacs are sprung
open using the outward tension stored in the gastralia
after exhalation. In birds, the need for this is
reduced, because they have ucinate processes on the
ribs that make the contraction/expansion of the
ribcage more uniform. Perhaps the need for more rapid
breathing forced birds to adapt this new respiratory
regime? What do you think?


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