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RE: whip tails

One of the arguments we use in the paper in that the fused caudal vertebrae,
found about half of the diplodocid specimens, are indeed such evidence. 

The fusion occurs in a region of the tail (caudal vertebrae 16 to 25) where
you would expect the maximum stresses to form. It happens to the place that
bullwhips tend to wear the most.  

Research by Rothschild & Berman (JVP, 1991, don't have full reference with
me) shows that the fusion of the caudal vertebrae in the diplodocids is due
to a process called DISH - diffuse ideopathic skeletal hyperostosis - which
occurs in many animal, including humans.  DISH occurs to relieve stress.

Also, in the same region, the caudal vertebrae are elongated - up to twice
as long at the maximum in the range 16-25 as they are in the early part of
the caudal series (caudal vertebrae 1-10).   This lengthening is not found
in non-diplodocid sauropods (such as Camarasaurus).  

Furthermore, the ratio of lengthing is more extreme in lightly built
diplodocids than in the heavier ones - it is 2.1 in Diplodocus, 1.8 in
Barosaurus and 1.28 in the much more robust Apatosaurus.

We argue in the paper that the lengthing of the vetertebrae was an
evolutionary adaptation to the stresses of tail whipping.   In some
individuals, this lengthening was supplimented with DISH.

Since the DISH tail fusion occurs in about half of the specimens
(admittedly, not very large numbers of specimens), it suggests that it was
sexually dimorphic.

Which in turn suggests that tail whipping (and thus supersonic tail
cracking) was done more by one gender than another.   This leaves the
intriguing suggestion that it was a form of sexual display.   Usually it is
males that get such features, so we could imagine that males cracked their
tails to attract females over long distances, or engaged in display contests
with other males.