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Re: 10/26 Science News Dino Articles: Urination, Pterosaurs, Mosasaurs,Stegos

Nick Gardner wrote:
> Sean Carroll wrote:

> >LOL ... nice to know that in an age of bitter controversy, dinosaur
> >science can still take a breather and prove some pretty obvious facts.

> I cannot say it was absolutely obvious to everyone that stegosaur tails were
> used as defensive weapons.  Didn't someone suggest their use as display
> structures?  One would think however that both were probably true in the
> end. (npi)

Not very likely, I think. Something like the sail of _Spinosaurus_, or
the crests of _Dilophosaurus_, or even _Stegosaurus_'s own back plates,
maybe (though personally I subscribe to the idea that the back plates
were primarily defensive and were able to move up and down). And perhaps
in a very loose sense, stegosaurs with bigger spikes might have been
more attractive to the opposite sex.

But can anyone think of a single instance when it is known that a long,
dangerous, sharp set of spikes is/was used primarily for display and not
defence? If you're going to grow something for sexual display, it makes
a lot more sense to make it something that won't disembowel your mates
should they accidentally fall on it, like antlers or crests or
feather/scale displays ... or pretty much *anything* else besides a set
of obviously deadly spikes. At best, I think they might have been sexual
attractants as an afterthought, in kind of the same way that some people
find a member of the opposite sex holding a huge gun (clearly something
invented for killing, not display) to be sexually arousing. And of
course they might have been used to intimidate rivals, as any sort of
weapon might be, but they seem (like the horns of advanced ceratopsians)
far too deadly to use for that frequently.

Also, weren't stegosaurs the only (or one of the only 2 or 3) groups of
ornithischians to totally lack a basketwork of bony caudal tendons for
stiffening the tail? (I seem to remember reading that in Bakker, but
feel free to set me straight, as I am really a theropod person.) What
possible sense would it make for stegosaurs to evolve one of the least
stiffened tails in the Dinosauria if they were not swinging those spikes
around as defensive weapons, but merely displaying them to mates and

If either of these stories is 'not immediately obvious', it's the
urination one, since (as someone posted after me and I did not stop to
think about -- d'oh!) most living dinos eliminate all their nitrogenous
wastes together in semi-solid pellets instead of urinating. But that
stegosaur tails could possibly have *not* been defensive weapons seems
totally illogical to me, though I am open to hearing why I could be