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On Sat, 17 Feb 1996, Ronald Orenstein wrote:

> A question; would the degree of horizontal vs vertical movement suggest that
> an ankylosaur would have been aiming mainly at an attacker's legs (with, I
> suppose, the aim of throwing it off balance) rather than generally flailing
> away at it (in which case rotation in three dimensions would be more useful)?

        By "attacker" do you mean a predator? The thing would have been 
the most useful piece of offensive weaponry an ankylosaur had against a 
predator, but it seems a good question as to whether it couldn't be used 
against other ankylosaurs. (I don't buy the stuff about the tail being 
too stiff. Why have those massive caudal ribs to attach muscles to if 
you're not going to be able to use those muscles?)
        I think we pretty much agreed recently that rhinos use their 
horns mainly against predators, not each other. It seems you could make a 
similar case for a Centrosaurus. Other animals have horns primarily for 
intraspecific combat- bighorns and giraffes(ossicones). Then there seems 
to be everything in between- male elephants are dependent on their tusks 
for securing females, but don't they also use them against predators?
Triceratops probably used those horns for defense, but scars also show 
up on frills from other Triceratops.
        The blunt weapons, though, would seem to imply that intraspecific 
combat is the main driving force behind their evolutiuon, and perhaps 
some are also of use against predators. If they were primarily 
anti-predatory devices, selection should cause them to become sharp and 
pointed like a rhinos horns. Cases like these among the dinosaurs seem to 
be Pachyrhinosaurus, Pachycephalosaurus, and the Ankylosaurs. (in the 
case of Ankylos and Pachyrhinosaurus, selection has favored the 
development of nonlethal weapons like clubs and blunt horns over lethal 
ones like shoulder spikes and sharp horns). Pachycephalosaurus had 
something that was basically a solid bone helmet- a high-impact 
head-butting device. Now, I believe that last time the issue came up, it 
was mentioned that Ankylosaur clubs were filled with spongy tissue. 
Somebody mentioned a similar, "foamy" texture for the Pachyrhinosaurus 
nasal boss, and suggested low-impact nose-butting. 
        I'd guess that they were both primarily used for low-impact 
combat, and perhaps throw in Shunosaurus and the Diplodocids as usingtheir 
for intraspecific combat. Imagine giraffes: the males swing their heads 
and thump each other in the sides with their ossicones. Then imagine 
something similar, but with the tails of Ankylosaurus, Shunosaurus, and
Diplodocus. (Don't try imagining this style of butting with 
Pachycephalosaurs, though, or your imaginary pachies might all break their 
imaginary ribs.
Those are high-impact structures, made of pretty solid bone, and probably
meant for head-to-head collision) The sexual dimorphism is a bit tricky.
Only male giraffes have ossicones 
(I think...). Pachyrhinosaurus has the structure in all individuals, but it 
appears much larger among some (presumably males). Some animals have horns 
in both, of course. But  for most dinosaurs, we don't have enough 
individuals to get a good look at sexual dimorphism and see how that 
prediction bears out.  
        anyways, those are my thoughts, hope its not too long-
        nick L.