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Monoclonius
''Monoclonius'' (meaning "single sprout") is a dubious genus of herbivorous ceratopsian dinosaurs found in the Late Cretaceous layers of the Judith River Formation in Montana, northern US, and the uppermost rock layers of the Dinosaur Park Formation in Alberta, Canada〔 dated to between 75 and 74.6 million years ago.
''Monoclonius'' was named by Edward Drinker Cope in 1876. Later, much taxonomic confusion was caused by the discovery of ''Centrosaurus'', a very similar genus of ceratopsian, that is known from much better remains. Today, typical ''Monoclonius'' specimens are usually believed to be juveniles or subadults, in many cases of other genera such as ''Centrosaurus''. Those specimens that remain under the name ''Monoclonius'' are mostly too incomplete or immature to be confidently matched with adult specimens from the same time and place. This is especially true of the type species, ''Monoclonius crassus''. Therefore, ''Monoclonius'' is now usually considered a ''nomen dubium'', pending further study.〔Ryan, M.J. (2006). "(The status of the problematic taxon ''Monoclonius'' (Ornithischia: Ceratopsidae) and the recognition of adult-sized dinosaur taxa. )" ''Geological Society of America Abstracts with Programs'', 38(4): 62.〕
==Etymology==
Contrary to what was stated in most popular or technical science publications prior to 1992, the name ''Monoclonius'' does not mean "single horn" or refer to its distinctive single nasal horn. In fact, the genus was named before it was known to have been a horned dinosaur, and had previously been considered a "hadrosaur". The name in fact means "single sprout", from Greek μόνος, ''monos'', "single", and κλωνίον, ''klonion'', "sprout", in reference to the way its teeth grew compared to its relative ''Diclonius'' ("double sprout"), which was named by Edward Drinker Cope in the same paper as ''Monoclonius''. In ''Diclonius'', Cope interpreted the fossils to show two series of teeth in use at one time (one mature set and one sprouting replacement set), while in ''Monoclonius'', there appeared to be only one set of teeth in use as a chewing surface at any one time, with replacement teeth growing in only after mature teeth had fallen out. This salient feature of the tooth, which specimen is now lost, almost certainly precludes it from being centrosaurine: it probably indeed is hadrosaurian and was by mistake associated with the rest of the type material.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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