Evolution theory posits that something like the Stegotharus’ tail developed for a reason.
Decorative displays are usually for sexual attraction of the opposite sex. And such displays are usually on only one sex of a species. For example, the male peacock has all the colorful feathers.
It’s hard to imagine a appendage shaped like a war club would be sexually attractive to both sexes of these animals unless they were both into S&M.
Hey, if humans are, why not stegos?