Cenoceras Hyatt, 1883

Weis, Robert, Schweigert, GÜnter & Wittische, Julian, 2023, A new giant nautilid species from the Middle Jurassic of Luxembourg and Southwest Germany, Swiss Journal of Palaeontology (24) 142 (1), pp. 1-11 : 4

Genus Cenoceras Hyatt, 1883

Type species. Nautilus orbignyi Prinz, 1906 (= Nautilus intermedius J. Sowerby, 1816 in Orbigny 1843, pl. 27), by original designation.

Remarks. There is great confusion about the nature, type horizon and stratigraphical range of Nautilus intermedius J. Sowerby, 1816 , which has been controversially interpreted by numerous authors (for a recent overview see Țibuleac et al., 2020). Tintant (1984), who tried to trace the illustrated specimen in the Orbigny collection, reviewed the Early Jurassic representatives of the genus Cenoceras . He assigned a specimen of this collection originally labelled as Nautilus striatus to Sowerby ʼ s species Nautilus intermedius ; however, this specimen has a much wider umbilicus than the specimen illustrated on Orbigny ʼ s plate 27, to which Hyatt (1883) explicitly referred when erecting his new genus Cenoceras . Tintant (in Enay et al., 1994) suspected that specimens were mixed up and that the illustration of plate 27 shows a chimaera by artificial combination of characters from various specimens of species of different ages and localities. Finally, he agreed that Nautilus intermedius sensu Orbigny was conspecific with Nautilus intermedius J. Sowerby, 1816 . However, interpreting the specimen illustrated on Orbigny ʼ s plate 27 as a non-existent taxon would make Hyatt ʼ s genus Cenoceras invalid, since Tintant did not formally designate a type for Nautilus orbignyi amongst Orbigny ʼ s Nautilus intermedius specimens. Treating N. orbignyi Prinz as a “ nomen nudum ” as suggested by Tintant (1984) is impossible, because its holotype is by definition the illustrated specimen of Orbigny ʼ s plate 27.

Of course, it is well-known that the illustrations of Orbigny ʼ s plates are highly idealized and standardized (the apertures always pointing to the left), but he provided measurements of a concrete specimen, most likely of the illustrated one. Amongst the 15 surviving specimens in the Orbigny collection labelled as Nautilus intermedius , the closest morphological resemblance is with a specimen (MNHN-F-A02204) from the Toarcian of Avallon ( Fig. 4 ) (Tintant in Enay et al., 1994). Tintant determined this specimen as Cenoceras astacoides (Young & Bird, 1822) , a species originally described from the Toarcian of Yorkshire, United Kingdom ( Howarth, 1962). MNHN-F-A02204 is the sole specimen of the surviving Nautilus intermedius material in Orbigny ʼ s collection that originates from the vicinity of a locality cited by d ʼ Orbigny (Tintant in Enay et al., 1994). Hence, we conclude that MNHN-F-A02204 was indeed the specimen on which Orbigny ʼ s plate 27 is based and which was subsequently assigned to a new species by Prinz, (1906), Nautilus orbignyi . Nautilus orbignyi Prinz, 1906 is here considered a subjective junior synonym of Nautilus astacoides Young & Bird, 1822 and, more importantly, the widely used genus Cenoceras can still be used in the strict sense of Tintant. We concur with Tintant (1984) that Nautilus intermedius Sowerby, 1816 is a species from the Sinemurian. The illustration of the holotype, however, is a very schematic drawing. Obviously this holotype is untraceable, because Foord (1891, p. 192) referred to several specimens stored in the collection of the British Museum but explicitly not to Sowerby’s illustrated specimen. Even the type locality of Sowerby ʼ s Nautilus intermedius, Keynsham in Somersetshire, was only cited with a question mark as a doubtful occurrence of this species. Tintant (in Enay et al., 1994) illustrated two nautilids of Orbigny ʼ s collection (MNHN-F-R09436 and MNHN-F-B48672) that he identified as Cenoceras intermedium (Sowerby, 1816) , however, these specimens were originally labelled as Nautilus striatus Sowerby and did not belong to the series of N. intermedius in Orbigny ʼ s collection. Thus, replacing the type species of Cenoceras Hyatt, 1883 by Nautilus intermedius Sowerby, 1816 without legitimation by the International Commission of Zoological Nomenclature was a clear violation of the principles of zoological nomenclature ( ICZN, 1999) and cannot be accepted.

Figures

Fig. 4 ‘Nautilus intermedius Sowerby’,from the d’Orbigny collection (specimen MNHN-F-A02204);Toarcian of Avallon (photo: courtesy of Muséum national d’histoire naturelle, Paris)