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RE: Diplodocid whip-tails



At 01:01 AM 11/14/97 +0000, you wrote:
>> 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
>
>
>
>Nathan, I am delighted to find that you are a subscriber to this list as I
have a question or two for you, although I will be certainly be looking
forward to your paper with Dr. Currie.
 Perhaps you are familiar with S.Czerkas's paper on spines occuring on the
tails of sauropod dinosaurs. His observations are based on specimens
obtained from diplodocids excavated by European commercial collectors who
are working the old Howe Quarries of Barnum Brown fame in Wyoming. Czerkas
illustrates these spines as occuring in the "whiplash" section of the caudal
vertebrae. Even more intriguing is the placement of these spines. They
eminate from above the articulation or joint of the caudal vertebrae. This
would seem to inicate a restriction of movement in this area. Any comments?
 I would like to add that others have excavated sauropods from very
fine-grained sediments in the Morisson Formation and have never encountered
these artifacts.
 Also, I would note that the Chinese sauropod, Shunosaurus, has a
well-developed tail club in its distal tail region. Perhaps this may have
been a trend in these animals. Whatever, I am most interested in your
comments. Thanks,
Dan Varner