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Re: mass, momentum, & misc.



Nicholas:

   1)  My impression of the structure of _T. rex_ is that its pubis is so
massive that _T. rex_ had a great, low center of gravity.  Its neck could
certainly flex into a short "S" shape, and its tail was massive.  This
probably would be enough to offset a 1000-2000 pound meal in a 8000 to 12000
pound animal.  It probably moved much slower after consuming a large meal,
much the same as we do when we overdo it!!

    2) Concerning pachycephalosaurs butting head like bighorn sheep - many
people have observed that animal that do butt heads or lock horns have an
even number of major protrusions.  eg. Triceratops - its nasal horn barely
got in the way - the other two horns could lock with another
triceratopsian's.  The skull of Stegoceras, etc. has the central dome of
skull and has some bony protrusions surrounding the dome.  I think that it
was more likely to use its head for real attacks, not ritualistic sexual
display attacks.  (ie. fighting off real enemies).  It is also possible that
they could have used their large domes for sexual contests, but pushing
contests, not bumping contests.

    3) The muskox scenario is as pure a speculation as one generally can
get.  There is absolutely no reason (ie. no fossil evidence) to support the
muskox idea.  (In fact, the muskox and wagon train movies are the places
that such actions are found).

    Allan Edels

-----Original Message-----
From: ngear@gvtc.com <ngear@gvtc.com>
To: dinosaur@usc.edu <dinosaur@usc.edu>
Date: Thursday, February 12, 1998 1:15 AM
Subject: mass, momentum, & misc.


>  I've been crawling around the Tyrrell Museum website (nice site, by the
>way) and find myself once again vexed with questions about dinosaur
physics.
>Does the T. rex reconstruction there represent contemporary thinking about
>how the rex most likely was built?
>( http://tyrrell.magtech.ab.ca/tour/trex.html )
>  I notice the forward view indicates the legs were placed very close to
one
>another.  This brought back to mind that question that has been pestering
me
>of where a rex would store a large meal (two tons, by at least one famous
>estimate).  If the legs were indeed spaced this closely together, I would
>think that would mean the bulk of a meal would have to be stored forward of
>the legs--and far enough forward at that so as not to seriously impede the
>motion of the legs.  Looking at the rex in profile, I find it hard to
>imagine where you could hang a two-ton meal mass on that skeleton forward
of
>the legs without seriously front-weighting the rex.  I fail to understand
>how it could have compensated.  (T.A., I thought your suggestion that maybe
>the rex could have used its flexible neck to pull its head back some had
>merit, but looking at that spine, my feeling is that this strategy would
not
>have gained much.  But perhaps someone out there has some actual figures as
>to how much the rex could have retracted it's head by flexing it's neck.)
>  I'm not just picking on the rex here, by the way.  Take a look at the
>Albertosaurus reconstruction.
>( http://tyrrell.magtech.ab.ca/tour/alberto.html )
>  What is going on here?  Does that look like an animal built to carry a
>heavy meal load up front?  From what I can tell, therapod experts don't
seem
>to think huge meals would have posed a balance problem for these guys.
What
>do they (or you) know that I don't?
>
>  While I'm going on about dinosaur physics, the Tyrrell had some displays
>on pachycephalosaurs which I found curious.
>At  http://tyrrell.magtech.ab.ca/tour/stegocer.html we see a scene
described
>as "A male stegoceras prepares to butt a rival in the ribs."  I have often
>heard pachycephalosaurs described as head-butters, much like bighorn sheep.
>Does this strike anyone else as peculiar?  Look at that flexible curved
>spine.  If the impact force decelerating that head is great enough to
>require such a thick skull (far thicker in proportion than the bighorns
seem
>to need) wouldn't the momentum of the body following the head fold up that
>spine like a wet soda straw?  I don't know.  If someone handed me a club
>that was round and blunt on the end, but with knobs and spikes surrounding
>the end, I think I would be more inclined to swing that club than thrust
>it--particularly if the handle was flexible.  (But then, I like to do
things
>the easy way.)
>
>  The Tyrrell brought up similar contests with regard to ceratopsians,
>saying: "Ceratopsians had a variety of horns, with which they probably
>battled members of their own species, just as deer and bighorn sheep do
>today.  They also had large bony frills surrounding their necks. The frills
>served as a means of display."
>  What the hey??  I was under the impression that the horns and frills were
>so that the ceratopsians could mass together, in the fashion of musk-ox, to
>present a horny, armored barricade against any would-be predators.  Was I
>just completely out in left field on that one?  And did female ceratopsians
>differ significantly from the males in armor and weaponry?  (My thinking
>being that sexual dimorphism would lend support to the notion that
>ceratopsians battled one another in contests much like deer and bighorn
do.)
>
>Confused,
>
>Nicholas (Wren)
>
>