Monoclonius (meaning "single sprout") is a dubious genus of ceratopsian dinosaurs found in the Late Cretaceous layers of the Judith River Formation located in Montana and Alberta. It has often been confused with Centrosaurus, a similar genus of ceratopsian. Monoclonius was described by Edward Drinker Cope in 1876. All Monoclonius specimens are now believed to be juveniles or subadults, in many cases of other genera such as Centrosaurus. Those specimens that remain under the name Monoclonius are too incomplete or immature to be confidently matched with adult specimens from the same time and place. Therefore, Monoclonius is usually considered a nomen dubium, pending further study.