Monoclonius

Monoclonius is the doubtful name of a ceratopsid dinosaur. It was a herbivore (plant-eater) It lived in North America during the Upper Cretaceous, about 76 to 73 million years ago.
"Monoclonius" was named by Edward Drinker Cope in 1876, soon after the first fossil specimen had been found in Montana. The specimen was a near complete skeleton with only the feet missing. It included skull material and the base of the nasal horn. Its name means "single stem" and refers to its teeth, which have a single root.
"Monoclonius" is now regarded as a "nominem dubium". It seems to be a juvenile stage of "Centrosaurus".