Why does a dog have a tail?
That question belongs in the Tails, Beaks, and Claws forum. Evo will be along soon to move this thread.
Its what people used to hold a dog by before the invention of the lead.
(Mainly for balance, I think)
Aside from the balance, it constitutes part of canine communications. It also covers the dog's arse to hold in the stink to make for more rewarding butt-sniffing.
Separate names with a comma.