Ceratopsinae, based on the family name Ceratopsidae Marsh 1888, has priority over Chasmosaurinae Lambe 1915 both in terms of its eponymous genus (Ceratops montanus Marsh 1888) and as a taxon with a phylogenetic definition (Sereno 1998). The recent reintroduction of the subfamily Ceratopsinae in place of Chasmosurinae (Sereno 1998) was not adoped by recent summaries, such as Dodson et al. (2004), but this appears to have been because they remained uninformed of the taxonomic issues surrounding this decision. Running the following by several ceratopsian taxonomists has generally met with favor.

Although the nonminotypical genus and species, Ceratops montanus, is generally regarded as a nomen dubium (e.g. Dodson et al. 2004), it is based on two sizable horn cores and an occipital condyle from near the top of the Cretaceous section in Montana (USNM 2411, Marsh 1888, Hatcher et al. 1907:figs. 103-104). The horn cores, although probably not from a fully grown individual, are large enough to place securely within Ceratopsinae (Chasmosaurinae) rather than Centrosaurinae. Even if the genus and species are considered nomina dubia or junior synonyms of Triceratops horridus, the family-group names derived from the genus stand (ICZN Art. 40A). It is not reasonable to defend the use of Ceratopsidae and Ceratopsoidea and then decline use of Ceratopsinae, when they are based on the same nominotypical genus. Chasmosaurinae gained currency only relatively recently, as the diphyletic cladistic structure at the base of Ceratopsidae was clarified. There is no case to be made for its long-term use, and it is here considered a junior synonym of Ceratopsinae.

The active definition is a first-order revision of that in Sereno (1998) that substitutes the nominotypical genus and species of the Centrosaurinae (Centrosaurus apertus) as an external specifier rather than the slightly more nested Pachyrhinosaurus canadensis. There seems little point in including a nomen dubium, Ceratops montanus, in the definition.