 Traditionally, "C. medius" had been considered the type species of "Cetiosaurus".In 1888 Richard Lydekker had formally assigned "C. oxoniensis" as the type species but by the modern rules of the ICZN one of the species named by the original author, in this case Owen, must be selected.In 2003, Paul Upchurch and John Martin determined that "C." "hypoolithicus" and "C." "epioolithicus" could not be used because they were "nomina nuda".