N. cookanum placed within the genus Nautilus, together with extant species based on their shared shell characters. Fossils of the species from the Late Eocene Hoko River Formation are noted as one of the two oldest occurrences for the genus  (with the other, older occurrence being N. praepompilius of the Paleogene).
N. cookanum, a species within the genus Nautilus, is grouped with other extant species based on shared shell characteristics. The fossils of this species from the Late Eocene Hoko River Formation are recognized as one of the two oldest occurrences for the genus (with the other, older occurrence being N. praepompilius of the Paleogene).