"Makoto Taniguchi"  wrote...
> I was wondering, what kind of purpose does tails serve on dogs, cats, and
so on?

Tails serve a wide variety of purposes, largely dependent on the owners'
species.  I'm not an expert, but here are a few that seem obvious to me...

Cats:  Balance;  Have you ever seen a cheetah (admittedly not a true cat,
but close enough) chase a Thompson's Gaxelle (in film or real life)?  The
gazelle uses both speed and quick course alterations attempting to evade,
and the cheetah's tail is used as a counter-balance during those turns to
stay on the gazelle's track.  Quite beautiful to see, with the tail swishing
out to almost 90 degrees (it seems) on the shaper turns.

Horses:  Insect protection;  Here's one you've likely seen, with the horses'
tails almost automatically chasing away large biting flies, etc.

Monkey:  Climbing;  Some monkeys, as well as othe animals such as the tree
sloth, use the tail as a fifth grasping appendage, which appears easily as
handy as any hand or foot for this use.

Birds:  Fligtht;   Rather analogous to the cheetah's tail, this is in almost
constant movement to maintain the correct angle of attack, etc.  Works much
like an airplane's tail.  Wonderful to see a close-up, slow motion movie of
a hawk or an eagle gliding, circling and hunting - the tail is constantly
making minor corrections in every which way, as the wings stay relativcely
motionless.

Fish/Cetacean:  Movement;  (You may not have wanted this in your "and so
on", but it applies.)  This shouldn't need explanation.

Warthog:  Anyone know?  When running, a warthog's tail goes up like a
flagpole, but I have no idea why(?)

Lots of others, but this might answer you sufficiently.  Regards, Brett.
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