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herbivores' weapons

Nicholas pointed out:

>>In any case, herbivores' weapons tend to evolve for intraspecific combat, 
>>and only later are sometimes turned against predators.  This makes 
>>theoretical sense.  An incipient horn is no use against a predator:
>An excellent and interesting point.  However, would you apply similar
>reasoning to spiked ankylosaur armor, club tails, spike tails, etc. (that
>being that incipient armor, spikes, and clubs would have been of no use

I certainly didn't intend to imply that armour usually evolves for 
intraspecific contests.  That would include spiny armour, which can later be 
employed aggressively.  Some ankylosaurs may have done this.  African 
porcupines certainly do, sometimes rushing backwards at a potential 
predator.  So that's an exception to my rule.

>against a predator)?  I'm guessing you would not push this principle so far
>as to propose stegosaur tail-whacking contests. (Would you?) 

Those spikes look too dangerous to be used for serious intraspecific 
fighting.  I wouldn't rule out some kind of threat display where stegosaurs 
showed how powerful and spiky their tails were, but rarely came to blows.  
It depends on whether tail spikes evolved from relatively safe knobs on the 
tail, or are an extension of already-sharp dorsal spines.  I think contests 
are likely in ankylosaurs and sauropods, however.  

I would argue that tails are a special case, because they can be used while 
fleeing.  I'd imagine that even an ordinary tail could be swung at a 
pursuing predator, perhaps knocking it off balance or keeping it from 
closing for the kill.  Thagomisers could evolve from this starting point.  
That makes sense to me, but unfortunately I think the phylogeny and 
stratigraphy shows that heavy, encumbering armour precedes tail weapons in 
ankylosaurs and glyptodonts.

>I do think you are right...

And I have to admit you're right.

>how I determine which is which.  
>Um... yes.  That is a problem.

Yes.  And early proboscideans used their tusks for feeding, as do pigs.  
Clearly all generalisations are unreliable.

                                                        All the best,