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cervical ribs

Just to give us a break from all of this talk of "reply-to", I thought
I might try to bring us back to dinosaurs by asking something I've
been wondering about for a while now.

I've noticed that a lot of theropod dinosaurs have ribs emanating from
their neck bones and I was wondering if anyone's given any thought as
to their possible adaptive significance.  Or actually, since it seems
like a great idea to have bones protecting the tubes running through
your neck, perhaps someone could suggest a rationale as to why these
bones have become greatly reduced or absent in the crown (living)
groups of terrestrial vertebrates.  On the one hand I might think that
these ribs would be lost in order to increase the mobility of the
neck, but given that the cervical ribs are relatively prominent in _T.
rex_ that would seem not to be the whole story.  _T. rex_ is thought
by some (e.g. Gregory Paul) to have killed by darting its head forward
to rip out a chunk of flesh and leaving a terminal injury in its
intended prey.  The described behavior couldn't occur without suitable
cervical felxibility.

Is it possible that instead of just protecting the plumbing in the
neck, the cervical ribs supported some structure that was lost or
never appeared in other lineages?

Anybody have any ideas?

Mickey Rowe     (rowe@lepomis.psych.upenn.edu)