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The use of offensive weapons (was Re: ANKYLOSAUR CLUBS *)

In defending the claim:

>> When a part of an animal evolves some kind of offensive purpose, it
>> usually is for intraspecies combat first.

Rob Meyerson asks us to:

> Consider horns in pronghorn.

There are at least three difficulties with Rob's argument.  First and
foremost is the assumption that structures evolve for a purpose.  Most
any modern biologist will tell you that the evidence indicates
otherwise.  Perhaps Rob is only using some shorthand here, but even if
so, I would advise him to use more caution than he's thus far
demonstrated.  Second is his implicit assumption that the use to which
pronghorns currently put their weaponry is the same as that to which
their protohorned ancestors put theirs.  This assumption wasn't even
stated let alone demonstrated.  Finally, Rob, you've been making very
strong statements about the use to which ankylosaurs put their tail
clubs.  You can't exactly expect us to accept that your statement is
true just because you've given us one example with no indication as to
why that example should be generalizable to ankylosaurs (or any other
animals, for that matter), can you?

To flip this around, Rob, how willing would you be to accept the
statement that ankylosaurs probably used their tail clubs to beat off
predators, if for justification all I said was "look at how catfish
use the spines on their fins"?

Mickey Rowe     (rowe@lepomis.psych.upenn.edu)