The species Chasmosaurus kaiseni, known from a nearly complete (but partially restored) skull on display at the American Museum of Natural History, shares features in common with Mojoceratops perifania and may represent the same species. However, the parietal (back margin of the frill) is not preserved, and was restored in plaster based on other Chasmosaurus specimens, which caused confusion among scientists in previous decades. Because the parietal bone is critical for determining differences between species in ceratopsids like Chasmosaurus and Mojoceratops, C. kaiseni is regarded as a nomen dubium, rather than as the senior synonym of M. perifania.