of Vertebrate Paleontology, he named "Taxon C" as a new genus and species, Achelousaurus horneri. Although an abstract was published containing a sufficient description, it did not identify a holotype, a name-bearing specimen. In 1995, in a subsequent article, Sampson indicated specimen MOR 485 as the holotype specimen of Achelousaurus horneri. The generic name consists of the words Achelous, the name of a Greek mythological figure, and saurus, which is Latinized Greek for lizard. Achelous (Ἀχελῷος) is a Greek river deity and a shapeshifter who was able to transform himself into anything. During a fight with Hercules, the mythical hero, Achelous took the form of a bull, but lost the battle when one of his horns was removed. This allusion is a reference to the supposedly transitional traits of the dinosaur and the characteristic loss of horns through ontogenetic and phylogenetic development, and thus through individual change and evolution. Dodson, in 1996, praised the generic name for being original and intelligent. The specific name honors Jack Horner, for his research on the dinosaurs of the Two Medicine Formation in Montana. Sampson also named "Taxon B" as the genus Einiosaurus in the same article wherein Achelousaurus was described. He said paleontologists needed to be cautious when naming new ceratopsian genera because their intraspecific variation (i.e., variation within a species) might be mistaken for interspecific differences (between species). Until 1995, only one new genus of centrosaurine dinosaur had been named since Pachyrhinosaurus in 1950, namely Avaceratops in 1986. Achelousaurus thus holds particular importance for being one of the few ceratopsid genera named in the late twentieth century. The holotype specimen MOR 485 was collected by Hostetter and Ray Rogers from the Landslide Butte Field Area about northwest of Cut Bank. In 1995 Sampson described it as the partial skull of an adult animal including the nasal and supraorbital (region above the eye socket) bosses (roundish protuberances instead of horns), and the parietal bones. Additionally, MOR 485 preserves some bones of the skull rear and sides, which in 2009 were listed by Tracy L. Ford as a right squamosal bone, the left squamosal, both maxillae, both lacrimal bones, both quadrate bones, both palatine bones, the braincase and the basioccipital bone. In 2015, Leonardo Maiorino reported that as part of the same specimen a fragmentary lower jaw has been catalogued as MOR 485-7-12-87-4. A right squamosal bone from another adult individual was recovered from