RE: supersaurus tail thingy

[Nathan Myhrvold <nathanm@intven.com>]

Since I am the main proponent of tails-as-whips and poppers, here are my
comments.

The popper or cracker on a bullwhip is typically just a frayed piece of
string.   The stress involved in creating the sonic boom is damped
exponentially as you move down the tip, so almost all of the wear is in the
last few millimeters of the whip.   The frayed end also promotes the
creation of the sonic boom shock wave.  It is possible to make a whip crack
without a popper, but it is easier and the crack is louder if you have one.

Lizard tails which are thin and pointed at the end, such as those of iguana
or varanid (monitor) lizards, typically have frayed dead skin at the end,
which is replenished after wear from the friction of tail dragging.  They do
not crack their tails like whips, but they do have dead skin at the tip
which could make an adequate popper.

Diplodocid sauropods (and possibily dicraesaurs as well) have tails which
our computer modeling and other work show are ideally designed as supersonic
whips.  This has been rehashed on the list many times, and I won't go
through it again now.  But if they did, it is very likely that they had a
popper.

The simplest popper would be dead skin at the end of the tail.  It would
only have to extend 6 inches or so to be a very effective popper - since the
tails were up to 45 feet or so, this is a very small proportion of the
length.  Poppers can be longer, and by scaling varanid tails, you could
imagine a dead skin popper that was several .  Skin generally does not
fossilize so this is unlikely to be confirmed by fossil evidence.  Absence
of evidence isn't evidence of absence.

The Howe Quarry in Wyoming has an unusually well preserved "mummified"
diplodocus tail specimen that exhibit triangular spines running dorsallly on
the mid portion of the tail - analagous to the dorsal spines on an iquana.
Czerkas, Paul and others have depicted sauropods with those spines.  I'll
point out that the Cecil the Dinosaur cartoon I watched as a child showed
Cecil with such spines - albeit without supporting scientific evidence.  A
modified verson of one of these spines could make a very effective popper.
It would probably be very thin - not a sail like extension, but rather a
thin, string like tip on the tail.

Unfortuately, the Howe Quarry specimen does not extend out to the end.
Perhaps a future specimen will.

Meanwhile, Omeisaurus has a tail club, which is quite different from a
popper.  The tail club is a set of 5 fused vertebrae. The diameter of the
club is much larger than the caudal vertebrae leading up to it, and the
surface seems to be rugose - which would suggest that it had a hard,
horn-like keratin covering.  A club needs to have this feature so that when
it strikes its target, the part that is involved in the collision is the
hardened club, rather that the "moving parts" of the joints in the caudal
vertebrae.  Ankylosaur tail clubs have this feature, and Omeisaurus does
too.

A thick, hard, heavy tail club like this could not be a supersonic popper.
The physics of momentum transfer that creates supersonic motion in a whip
requires the mass to DECREASE as you move toward the end of the whip - the
Omeisaurus club is much heavier.  It seems to be adapted as a club or impact
weapon.

Nathan

-----Original Message-----
From: John Schneiderman
[mailto:jschneiderman@revelation.lib.unomaha.edu]
Sent: Friday, February 16, 2001 6:42 AM
To: dinosaur@usc.edu
Cc: dinosaur@usc.edu
Subject: Re: supersaurus tail thingy


On the same line, is it possible that the club-like tail feature found in
the Chinese Omeisaurus may also be a "popper"?  The club-like feature a
product of fossilization.