Dodson believed one species of "Monoclonius", "M. nasicornus", may actually have been a female "Styracosaurus". His assessments have been partially followed, with other researchers not accepting "Monoclonius nasicornus" as a female "Styracosaurus", or "Monoclonius" as a valid genus. While sexual dimorphism has been proposed for a more basal ceratopsian, "Protoceratops", there is no firm evidence for sexual dimorphism in any ceratopsid. Others have synonymized "C. nasicornus" with "C. apertus", or considered it a separate "Centrosaurus" species: "Centrosaurus nasicornus". It has also been suggested as the direct ancestor of "Styracosaurus albertensis". A 2014 study of changes during growth in "Centrosaurus" concluded that "C. nasicornus" is a junior synonym of "C. apertus", representing a middle growth stage.