Monoclonius

Monoclonius (meaning "single stem"; referring to the teeth, which have a single root) was a ceratopsian dinosaur from the Judith River Formation of Late Cretaceous Montana and Canada. It is often confused with Centrosaurus, a similar genus of ceratopsian (some think the two may even be identical, of a different age or gender). Monoclonius was described by Edward Drinker Cope in 1876.

Diet and ecology
Monoclonius, like all Ceratopsians, was a herbivore. During the Cretaceous, flowering plants were "geographically limited on the landscape", so it is likely that this dinosaur fed on the predominant plants of the era: ferns, cycads and conifers. It would have used its sharp Ceratopsian beak to bite off the leaves or needles.