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On Fri, 18 Apr 1997, Rob Meyerson wrote:
> 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...
Does Eoraptor or Herrerasaurus display pneumatic dorsal and/or
cervical vertebrae? We were bandying about just when and why
pneumaticity arose here in the lab, and since Cathy Forster is not around
to shed light on the subject this week and since Rob posed the
No ornithischians display pneumaticity (Britt, 1993). As for my
beloved sauropods, the dorsal vertebrae of Barapasaurus and Kotasaurus
disply a depression at best, but don't appear to be pneumatized (though
personal observation this summer should remove any/all doubts...), but
fast forward a few million years and, wah lah! Also, some beasties like
Dicraeosaurus don't have 'em, or at least not the "classic" kind, and
then dip into the titanosaurids and one finds *camellate* centra! Weird
stuff indeed. I confess my ignorance in theropod pneumaticity
(having last read all of Britt, 1993 in 1994...) but am curious as to
when it first appears. How about segnosaurs? Any signs of it there?
And what is it for? The two arguments I always hear, "lighten the load"
and "physiologic necessities" aren't *that* convincing, as the former
doesn't seem to make *that* much of difference.
Besides, air sacs appear first in small beasties, so lightening doesn't
make sense (but then again, we all know how evolution makes common
sense). Physiology might work, but some of those small active croc-forms
looked pretty active. This is a contentious topic that has probably come
up before, so I will have to go forth and cruise the old posts this
weekend. I look forward to any/all response, on list preferably because
I know many of the lurkers have curiousities regarding this issue!