RE: Dinosaur tail dragging

["Stewart, Dwight" <Dwight.Stewart@VLSI.com>]

Okay, I'll "bite"! :-)  I'm a physicist, not an engineer, but this is mostly
physics anyway. :-)

Gravity is a big factor on any body, but luckily - the bigger a living
organism is (normally) the stronger it is.
Pound per pound, gravity pulls on everything the same.  We "overcome"
gravity every time we move or simply stand erect.  So, yes - indeed -
gravity tends to pull a tail down.  BUT - we all evolved to deal with
existing gravitational force.  Muscles & bones are one way to accomplish
this, but the over riding issue is structural or tensile strength.  Rigidity
is a more robust way of overcoming the pull of gravity than simple muscle
strength, in which (no matter how strong the muscle is) it tends to tire,
because gravity is relentless.  So, bone structure & ligament & tendon
attachment point AND tensile strength are more important than muscle
strength, which is more an issue in movement than RESISTING movement.
The drag coefficients on a big, heavy saurapod OR hadrosaur, or ANY heavy
tail are enormous.  And the friction between such a tail & the ground would
further compound the drag.  An alligator drags its tail, BUT - look at how
it's body is positioned: very low, in an almost straight pull line with the
tail AND with the legs sprawled out at the sides.  If you have ever seen a
power lifter do a lift from ground, you will get an idea of the forces that
must be overcome.  Now, if a heavy tail is stiffened due to skeletal
position and reinforced with tendons & ligaments, then much less effort must
be expended to resist gravity.  True, such a tail would not technically be
at rest, but it could be held in a state of equilibrium, in which the
natural downward pull of gravity is checked in a relatively relaxed manner.
Some muscle tension is always present in a body being held at a non-rest
(non ground) position, but the amount of energy expended can be reduced to a
negligible level with adequate suspension.  And, if the suspension is
supported well enough, only one point of attachment to a body that is at
ground position is required.  A joint would greatly complicate the issue.  A
joint with very limited range of motion (if any) would be best for this
purpose.
No joint would be the ideal situation.

Dwight
        -----Original Message-----
        From:   PTJN@aol.com [SMTP:PTJN@aol.com]
        Sent:   Saturday, September 05, 1998 11:56 AM
        To:     dinosaur@usc.edu
        Cc:     102354.2222@compuserve.com
        Subject:        Re: Dinosaur tail dragging

        In a message dated 9/4/98 10:55:25 AM Eastern Daylight Time,
        102354.2222@compuserve.com writes:

        <<  In a talk with Don Burge (College of Eastern Utah) a couple of
years ago,
        he informed me that several of the now-closed sections of coal mine
in the
        vicinity of Price, UT (where most of the famous coal mine prints
have been
        found) show lengthy sections of trackway of probably hadrosaur and
ceratopsian
        origin with long tail drags. >>

         A question for Jerry or for some engineers out there (Jim
Cunningham?): Would
        it be energetically less expensive for an animal like a large
sauropod to hold
        its tail off the ground or to drag it?  In the first instance, you
are
        fighting gravity and in second, friction (not to mention wear and
tail on the
        tail itself).  A lot of assumptions are necessary for this type of
        estimate--all of which others on this list are better able to
describe than am
        I. Among them-(in a "tails up" scenario) what is the contribution of
ligaments
        to holding the tail off the ground (thereby offsetting any muscular
energy).
        In a "tails down" scenario, what was the mass and the friction
coefficient of
        a dinosaur tail?  How much time did they spend moving, as opposed to
standing
        still?

        Personally, the (overwhelming) absence of tail drag traces among
dinosaur
        trackways leads me to believe they did not drag their tails.  But
I've never
        seen an analysis of this based on erergetics.

        Pat Norton