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RE: T rex brooding




        -----Original Message-----
        From:   Jaime A. Headden [SMTP:qilongia@yahoo.com]
        Sent:   Wednesday, August 19, 1998 12:15 AM
        To:     dinosaur@usc.edu
        Cc:     Dwight.Stewart@VLSI.com
        Subject:        RE: T rex brooding

        Dwight Stewart wrote:

        <If its arms were entirely useless, then why didn`t evolution
        eliminate them altogether?>

          Probably because they weren't entirely useless. Instead of
rendering
        the digits totally vestigial, the adaptive process of evolution
        enabled tyrannosaurs to reduce to two, and those two fingers became
        highly mobile, with joints at the metacarpals that gave it a
        spreading-when-extended and narrowing-when-flexed range of motion.
It
        was a specialized hand.

        <Even with limited flexion at the "shoulder joint" (or perhaps,
nearly
        none!) that's enormously strong for a 'human sized' limb.>

        [snip ...]

        <IF the tyrannosaur forelimbs were as strong as some infer, that
would
        seem to work in favor of 'breasting'.>

          The humerus was limited to about 30 degrees of fore-aft movement,
        most of it centered on the veritcal.
          The elbow was limited to a 20 degrees or so off the vertical to
        strait forward and perhaps 10 degrees above the horizontal.
          The wrist could twist a little (I think) and could still bend up
and
        down rather well, plus the fingers were mobile [above].

          It could lift, but could not "brood" with the arms simply becuase
        they were not long enough to cover anything unless the chest were
        firmly down on the ground, and then _that_ would be a rather awkward
        situation, wouldn't you say?

          The rather surprising conclusion (from a few members on the list
        whose names, but for the esteemable Dr. Holtz' and perhap Ralph
Miller
        III, I can't seem to remember) that I see is that these were like
        little chain hooks, to latch onto brush and debris and drag it to
the
        nest, or prep the mound, build it up, perfect it and hang the
        curtains, a task that probably took days, would actually be
        accomplished well.

          The animal wouldn't even need to lay its chest down to do any of
        this, just tilt the forequarters down and twist the head sideways so
        it can see below it (a little, I'm sure) or do it by feel, if at
all.

        ==
        Jaime A. Headden

        Okay.  Thank you,  With this information, I'd be inclined to agree
with the mound building
        Nesting hypothesis.  AND using the forelimbs as "chain hooks" would
seem to be a good,
        Functional explaination for tyrannosaur arms.
        This is a TAD off subject, but on a tangent to it: (I may have asked
this earlier), but do we have
        A working biomechanical model of how an adult tyrannosaur would rise
from a prone posture?
        What I had in mind (as an example) is the potential situation of a
prey animal knocking a
        Tyrannosaur off its feet.  How would the tyrannosaur regain a
standing posture AND could it 
        Accomplish this with speed?  

        Dwight