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RE: Diplodocid whip-tails



> Dann Pigdon wrote:
> > 
> > I read an article in a newpaper recently about a computer
> > scientist (Dr Nathan Myhrvoid) who suggested that diplodicid
> > tails were actually used as giant bull whips to make loud
> > cracking sounds. Does anyone else find this unlikely? The end
> > of a whip usually has to be replaced occationally because of
> > the damage caused by it breaking the sound barrier. Unless
> > sauropods had a very high pain threshold and could regrow the
> > ends of their tails, I imagine attempting to crack their tails
> > like a whip would be a painful and damaging exercise.
>  
[Nathan Myhrvold]  

I am a poor choice as somebody to find it unlikely, but here is an answer
anyway.

First, the paper on this work will be in the next (Winter 1997) issue of
Paleobiology, so you can see the full argument there.  Discover Magazine did
an article on it that covers some of the issues, but go to the real paper
for serious details.

Second, I want to make it clear that Phil Currie (who co-authored the paper
with me) do not claim to have *proven* that the diplodocid sauropods had
supersonic tails.   It is very difficult to prove a behavioral
characteristic given only fossil remains.

However, we have tried to show that it was physically plausible.   One of
the first objections that most people have to supersonic sauropod tails is
that supersonic motion will damage the tail.  Partly this is because people
associate supersonic motion with exotic materials in fighter jets or the
Concorde.  But bullwhips made of cow hide and similar organic materials last
a very long time.  

The very end of the whip, called a popper or cracker does wear away, and
eventually needs to be replaced.  In a tail, the corresponding area
subjected to shock would be very small, possibly only the last centimeter,
or at any rate a few centimeters.  This area would have to be toughened, but
no more so than other areas where skin becomes calloused.   The tissue on
the base of the feet and other areas are arguably more prone to damage.


If the diplodocids evolved their amazingly long tails for this purpose,
which is a highly derived feature, it does not seem unreasonable that they
would also have developed a bit of dead skin, or keratin, or other wear
resistant material at the tip to absorb or cope with the shock.  Like
fingernails, this could be constantly growing so it could be replenished
through wear.

Nathan