Doedicurus

Double strike
Its tail club was probably used in intraspecific conflict rather than defense against predators like Smilodon, in contrast to the superficially similar club of the ankylosaurs, which are thought to have been used to defend against predatory dinosaurs. For one thing, the latter use would have been difficult since the animal's field of vision was so limited that it would essentially have had to blindly thrash the tail club.