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RE: Tyrannosaur stance Question



   Thanks to Dann and Allen for the detailed reply! :-)  That certainly
answers my 
Question.  The Bataat model is perhaps a few degrees below horizontal & that
is probably the issue.  From your description, the hip girdle would provide
a lower center 
of gravity, thus making a more horizontal stance much more likely.  Also, it
seems I fundementally underestimated the robustness (& perhaps length) of
the Tyrannosaurus rex tail.  Recent information regarding older T. rex
mounts ACTUALLY be fitted with an Allosaurus type tail rather confused me.
:-).  Also, I wasn't taking the lungs into account.  I know MY center of
gravity was moved up about 6 inches in 1989, when I had my shoulders
replaced with titanium-steel alloy (arthritis).  Swimming was a big part of
my therapy & I quickly discovered that I could not longer float on my back
very easily.  When I mentioned my, er... "sinking" feeling, the surgeon
quipped; "Oh, yes,
with your size, these prosthetics moved your center of gravity up, perhaps 5
or 6 inches."  
   So, with a very sturdy hip structure, a Tyrannosaurus rex was constructed
something like a tetter totter, with the hips as the fulcrum?  Anyway,
that's how I'm visualizing it.  As far as the sacs or spaces in the
Tyrannosaurus rex skull; it seems that I recall something about Dr. Bakker
running a wire hanger (??) inside these areas inside the skull.  Or was that
Dr. Currie?  That would certainly lighten the huge skull, but I wonder if
that was the only function for those air sacs?  Once again - speculation.
It also seems that the tail could serve as a sort of rudder for better
turning while walking quickly or running.  But - I too am weary of
revisiting the "how fast could T. rex run" thread. :-) 
   As far as weighing a model in water, in my graduate school days I
sometimes worked at the hydrostatic unit at my university.  Primarily, we
weighed people to determine body fat percentages.  Basically, you weigh the
subject dry, then submerge them in a tank, sitting or standing on a weighing
platform. The person (or whatever) will weigh less when submerged, because
fat & air are less dense than water, while everything else is more dense.
You then crunch the numbers in a hydrostatic equation & you get the
percentage of lean body weight VS. fat (and air).  Only, if the subject
didn't expell most of the air from their lungs when submerging, they would
calculate out as having LESS lean body weight than they really did.  So, the
procedure was not perfect.  But,
the theory is sound physics.  In a way, measuring an inanimate object like a
model could be viewed as more accurate if the relative density is correct.
Another point to consider here is that a given volume of muscle tissue
weighs much more than the same volume of fat tissue.  With a human it is ~
2.5X heavier.  The new information regarding Tyrannosaurus rex indicates a
leaner, more muscular specimen than the old paradigm suggested.  BUT, that
might not mean that Tyrannosaurus rex actually weighed
a great deal less than the old model.

Anyway;
Thanks, Guys

Dwight 
 
        -----Original Message-----
        From:   Allan Edels [SMTP:edels@email.msn.com]
        Sent:   Sunday, September 20, 1998 12:23 AM
        To:     dinosaur@usc.edu
        Subject:        Re: Tyrannosaur stance Question

        My response to Dwight's question, and to Dann's answer:

        1)    Most modern mounts of _T. rex_ try to show the animal in an
active
        pose, probably running.  This means that the tail will be straight
back,
        parallel to the ground, with the head leaning closer to the ground
than it
        likely was at rest.
        2)    The mounts are supported by steel posts, and sometimes by guy
wires
        from the ceiling.
        3)    Many of the latest models are based on the modern mounts, i.e.
        running.
        4)    Look carefully at the pubic boot.  It is nearly 60% the length
of the
        skull, and it is a bit more solid than the skull. It is a large,
heavy
        construct.  It gave _T. rex_ a low center-of-gravity, and as Dann
mentions,
        the tail was heavy, and fairly solid, whereas the front of the
animal would
        have lungs and other air sacs, etc.
        5)    The tail, like many other dinosaurs, probably had a set of
strong
        tendons that ran most the length of the tail, stiffening it.  (Some
dinos
        had ossified tendons there, but it may be that we don't have an old
enough
        _T. rex_ to show them - and those _T. rex_s that were old enough,
the
        tendons were not collected).
        6)    The likely true standing pose of _T. rex_ would be with the
tail
        drooping 5-10 degrees towards the ground (below parallel), and with
the ribs
        and shoulders lifted around 12 degrees above the parallel to the
ground.
        The head would most likely be a bit above that angle.  Standing like
that,
        a properly built _T. rex_ model wouldn't fall over.
        7)    WAY BACK (but not quite Mesozoic) when I was a child, I used
to prop
        my toy _T. rex_ leaning over the back of _Triceratops_, too.
However, I
        just thought that it would look better that way - who knew that they
would
        change the stance to match my preferred pose?

            (As an aside to point 4 above:  R. MacNeil Alexander, in his
great
        (short) book about dinosaur and other extinct animal mechanics, used
plastic
        models [from the British Museum, I believe] to determine the correct
center
        of gravity, the specific gravity, and the displacement of each
animal.  To
        .be sure about the center of gravity, he drilled out an area
equivalent to
        location and size of the lungs.  He used different models to measure
the
        displacement.  Greg Paul told us (DML) that he [GSP, that is] would
take the
        best reconstructed model, modify it as he thought it should be, then
grind
        up the plastic to determine displacement, and thereby, how much the
animal
        weighed).

            Allan Edels


        -----Original Message-----
        From: Dann Pigdon <dannj@alphalink.com.au>
        To: dinosaur@usc.edu <dinosaur@usc.edu>
        Date: Saturday, September 19, 1998 7:50 PM
        Subject: Re: Tyrannosaur stance Question


        >Stewart, Dwight wrote:
        >>
        >> I have a question that I have been attempting to get a clear
answer on
        for
        >> some time.
        >>    So, here's my question: what features have led to the
conclusion that
        >> Tyrannosaurus rex walked, ran, and (perhaps) primarily stood with
its
        body
        >> almost horizontal?  Do you agree with this paradigm?  And, if
        Tyrannosaurus
        >> rex did move & stand in this posture, COULD he (or she) have
stood more
        >> erect.
        >> I understand (I think :-)) that the paradigm that birds tend to
hold
        their
        >> bodies at that angle (some birds, anyway) could open the question
up, but
        >> the physics of the very horizontal stance look awkward to my
eyes.  By
        that,
        >> I mean that if one takes the hip structure as the fulcrum, then
the front
        >> end of the Tyrannosaurus rex appears to be over-balanced with
respect to
        the
        >> tail.
        >> I know the T. rex head had many air pockets and that the small
arms would
        >> also tend to damper this effect.  Nevertheless, the tail doesn't
seem
        quite
        >> long or robust enough to balance out the structures anterior of
the hips.
        >> Am I missing something here?
        >
        >Okay, I'll try to say something remotely scientific here (gasps of
        >horror). The tail would have been solid bone, muscle, sinew, etc,
        >whereas the body had lungs and connected air sacks, and various
        >weight saving features. A model tends to be solid all the way
through
        >(or hollow all the way through, depending on the size I expect).
        >That said, I too tend to reconstuct a standing Tyrannosaur with a
        >VERY SLIGHT upward tilt of the body towards the front. Not as
extreme
        >as in birds (which lack counter balancing tails), nor as extreme
        >as the near-bipedal tail-dragging reconstructions that once
abounded.
        >However when moving, at a brisk walk or at a run (if that was
        >possible - no that isn't a topic for a new thread, just let it go),
        >I suspect the body would have levelled out (even blackbirds do
        >this when they run across a lawn).
        >
        >> What made me ponder this is that I collect
        >> 1/40th scale museum quality dinosaur models and the Bataat model
was
        touted
        >> to me as the most accurate representation of what the T. rex
looked and
        >> stood like.  SO, I bought one and it has this rather nasty habit
of doing
        a
        >> nose dive when it stands alone.  I asked my friend at the
Dinosaur World
        >> Store about this and he stated; "Gee, they ALL do that."  :-)  My
        solution
        >> was to pose my Tyrannosaurus lurking over (propped up) on the
back of my
        >> Triceratops.
        >>
        >> Dwight
        >
        >Have you ever tried to balance a Barbie doll on its feet (or any
        >doll for that matter)? Yet we know that humans can stand in a
bipedal
        >fashion. A dead, static model does not have the complex
        >inner ear arrangement of a living creature (surprise surprise). I
        >wonder how much luck you would have trying to get a model of a
        >sleeping flamingo to stand upright on one foot?
        >
        >--
        >____________________________________________________
        > Dann Pigdon
        > GIS Archaeologist
        > Melbourne, Australia
        >
        > Australian Dinosaurs:
        > http://www.geocities.com/capecanaveral/4459/
        > http://www.alphalink.com.au/~dannj
        >____________________________________________________
        >