In his original description of the "Ceratosaurus nasicornis" holotype and subsequent publications, Marsh noted a number of characteristics that were unknown in all other theropods known at the time. Two of these features, the fused pelvis and fused metatarsus, were known from modern-day birds, and according to Marsh, clearly demonstrate the close relationship between the latter and dinosaurs. To set the genus apart from "Allosaurus", "Megalosaurus", and coelurosaurs, Marsh made "Ceratosaurus" the only member of both a new family, the Ceratosauridae, and a new infraorder, the Ceratosauria. This was questioned in 1892 by Edward Drinker Cope, Marsh's rival in the Bone Wars, who argued that distinctive features such as the nasal horn merely showed that "C. nasicornis" was a distinct species, but were insufficient to justify a distinct genus. Consequently, he assigned "C. nasicornis" to the genus "Megalosaurus", creating the new combination "Megalosaurus nasicornis".