"Ceratosaurus" gives its name to the Ceratosauria, a clade of theropod dinosaurs that diverged early from the evolutionary lineage leading to modern birds. Within the Ceratosauria, some paleontologists proposed it to be most closely related to "Genyodectes" from Argentina, which shares the strongly elongated teeth. The geologically older genus "Proceratosaurus" from England, although originally described as a presumed antecedent of "Ceratosaurus", was later found to be unrelated. "Ceratosaurus" shared its habitat with other large theropod genera including "Torvosaurus" and "Allosaurus", and it has been suggested that these theropods occupied different ecological niches to reduce competition. "Ceratosaurus" may have preyed upon plant-eating dinosaurs, although some paleontologists suggested that it hunted aquatic prey such as fish. The nasal horn was probably not used as a weapon as was originally suggested by Marsh, but more likely was used solely for display.