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a question of balance

    At the risk of pulling down the ire of everyone who is sick of the aging
T-Rex-as-scavenger controversy, I have a question of a rather obvious
nature.  If T-Rex was too slow to catch the smaller, more agile dinosaurs,
could it not have specialized the other direction--in killing very large
prey (where the need for speed would not be so critical)?  I would think
that if you were going to go after a large herbivore, what you would need is
the ability to remove lots of meat, very quickly, fairly high up, and the
Tyrannosaurid form would seem a natural for this.  I would think talons
would not be very effective on the big herbivores 1) because the target zone
is too high, and 2) because of the limited depth a talon can cut, so the big
mouth would seem the better weapon for getting in deep to the vital bits
fast.  (And why would a scavenger need a mouth that big anyway?)  The
bipedal form has advantages for predation in that it confers some measure of
agility as well as raising the strike zone, but it carries a penalty in that
it requires balance.  Because of this, given the size of that head, T-Rex
either had to add tail mass (entailing more fuel consumption, more momentum,
more polar moment, and less agility) or sacrifice useless weight up front
somewhere (arms for example).
    The balance problem raises another question.  Is there anything to
indicate where the stomach of T-Rex was?  I'm guessing it was forward of the
legs.  Assuming the tail mass was not especially variable, I would think
this would tend to impose an upper limit as to how much a Rex could load up
during a single feeding since it would only be able to compensate for it's
forward-migrating center of gravity by changing it's stance (and shortening
it's stride).  Taking this further into the realm of pure speculation, the
size of T-Rex suggests it ate a lot, but the balance problem suggests the
size of any one meal was rather limited--suggesting it ate frequently.  This
raises an obvious problem for T-Rex as scavenger, as it would need an
amazingly constant supply of corpses.  The remarkable drop-dead rate this
would require would seem to me to be difficult to explain.  But the balance
limitation also raises a problem for T-Rex the hunter.  Either T-Rex went
for game small enough it could eat entirely without upsetting it's balance
(which doesn't seem likely as T-Rex does not seem well-suited for going
after small game) or it went after the huge game it seems almost tailor-made
for, and then couldn't eat most of it's kill.  Actually, I should have said
this is a problem for T-Rex the *solitary* hunter.  But what if it didn't
hunt alone?  The disadvantage of hunting in a pack would have been that it
would have had to share each kill--meaning it would give up meat it couldn't
carry off anyway.  The advantages of hunting in a pack would have included:
more frequent meals, the ability to go after more types of prey, the ability
to work a herd better, less energy expended in chase, less speed required
(if the hunting tactics are sophisticated enough), better ability to halt
the victim by mobbing it, and generally quicker, easier, and safer kills.  I
would also think pack hunting would have put less strain on prey populations
for wasting less meat per kill.  One big herbivore could have fed a lot of
Rexes to capacity.
    Given the complete lack of corroborating track evidence, this is, as I
said, in the realm of pure speculation.  But it seems to me that this line
of speculation is at least as plausible and legitimate as that which lead to
the T-Rex-as-scavenger proposal.  But then, my knowledge of dinosaurs is
pretty limited compared to most in this group.  Perhaps someone out there
knows of something fatal to the notion of T-Rex-as-pack-hunter.  I would, of
course, be interested to hear it.  Sorry about the length on this.

Nicholas Wren