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Re: Belly Ribs
>Since they are only known in saurischians, this must mean that
>theropods and sauropods had different breathing mechanisms. Or, possibly
>gastralia were used to hold in the visceral mass, or had a purpose or
>that nobody has even guessed at.
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? I am much more partial to
the respiratory system argument. Could it be assumed (if direct evidence
doesn't exist) that the most basal Saurischians had gastralia and if so,
were these gastralia used as part of a more efficient cardiovascular
system that aided these creatures in their carnivorous predatory
lifestyle? Sauropods then would have retained them and birds could have
eventually lost them.