Size and Weight:
It was probably too dumb to notice the difference, but Centrosaurus was definitely lacking when it came to defensive armament: this ceratopsian had only a single long horn, compared to three for Triceratops and five for Pentaceratops. Like others of its breed, Centrosaurus' horn and large frill probably served dual purposes: the frill as a sexual display and (possibly) a way to dissipate heat, and the horn to head-butt other Centrosaurus adults and intimidate hungry raptors and tyrannosaurs.
Recently, paleontologists announced a pair of new North American ceratopsians that seem to have been closely related to Centrosaurus, Diabloceratops and Medusaceratops--both of which sported their own unique horn/frill combinations reminiscent of their more famous cousin (hence their classification as "centrosaurine" dinosaurs, albeit ones with very Triceratops-like characteristics as well). Given the profusion of ceratopsians discovered over the last few years, it may well be the case that the evolutionary relationships of Centrosaurus have yet to be fully sorted out.