Cymatoceras reussi

Frank, Jiří, Sklenář, Jan & Ekrt, Boris, 2014, Late Cretaceous Nautilid Juveniles Of Cymatoceras Reussi And Eutrephoceras Aff. Sublaevigatum - Scarce Fossils Under Risk Of Pyrite Degradation, Acta Musei Nationalis Pragae Series B 70 (3 - 4), pp. 143-152 : 145

Cymatoceras reussi

(FRITSCH IN FRITSCH ET SCHLÖNBACH, 1872)

Pl. 1, fig. 1

non 1845 Nautilus inaequalis SOWERBY ; Reuss, p. 21, pl. 7,

fig. 12. p. 1872 Nautilus reussi FR. IN FRITSCH ET SCHLÖNBACH ,

p. 25, pl. 12, figs. 4.a,b.

1897 Nautilus reussi FR. ; Frič, p. 36.

1898 Nautilus reussi FR. ; Frič, p. 35. p. 1934 Nautilus reussi FRIČ ; Andert, p. 392. p. 1956 Nautilus reussi FRITSCH ET SCHLÖNBACH ;

Kummel, p. 344.

L e c t o t y p e: NM-O3166. The specimen is in the collections of the National Museum in Prague. This specimen is the only one preserved and figured specimen of C. reussi which according to the emended diagnoses can be determined as the lectotype. The rest of the syntype collections after this revision belong to Eutrephoceras aff. sublaevigatus .

T y p e l o c a l i t y: Vinařice near Dobrovice.

T y p e h o r i z o n: Upper Coniacian, Březno Formation,

Frič’s layer No.6 (?).

E m e n d e d d i a g n o s i s. Nautiliconic, involute shell, slightly compressed whorl in cross section, broadly rounded ventral side, numerous phragmocone chambers, sinuous suture line with umbilical saddle, prominent lobe on the inner lateral side, saddle on the lateral side, lobe on the outer lateral side and saddle on the ventral side. Siphuncle barely noticeable in central/ventro-central position. Reticular sculpture on the surface of early juvenile shell (This diagnoses is based on the single juvenile specimen NM-O3166).

D i s c u s s i o n. A. Frič described (in Fritsch and Schlönbach, 1872) several specimens from Chlomek, Březno and Lenešice locality and identified them as a new species “ Nautilus reussi ”. Nevertheless the group of specimens described by Frič contains two different species. One of the specimens, NM-O3166 (Pl. 1, fig.1), can be correctly considered as a new species, Cymatoceras reussi , due to its specific suture line and numerous phragmocone chambers. As Frič mentioned himself, this specimen is unique in its morphology among the Bohemian Cretaceous Basin cephalopod fauna and it was for this reason that he described it as a new species. The specimen represents initial juvenile whorls of a larger specimen as indicated by the umbilical columns. The reticular pattern on the surface represents the typical surface morphology of nautilid juveniles in the pre-hatching state (e.g. Chirat 2001; Arnold et al. 2009). The other specimens from the group are described in this study as Eutrephoceras aff. sublaevigatum .

Frič considered C. reussi as a potential juvenile specimen of Cymatoceras deslonghampsianum (D’ ORBIGNY, 1840) from the Cenomanian. This species has numerous chambers and a similar sinuous suture line but less prominent ventral saddle. Specific for C. deslonghampsianum are the prominent radial ribs with fine cross lines emerging during ontogeny after hatching which Frič also considered in his comparison. In the pre-hatching state there are the same reticular patterns as in all other post Triassic nautilids. Another specific feature is the prominent sharp edge on the umbilical inner lateral side. This feature cannot be confirmed on the C. reussi juvenile specimen due to its state of preservation. The siphuncle position in C. deslongchampsianum is centro-dorsal, but on C. reussi it seems to be central or slightly ventro-central.

Other Cenomanian species resembling C. reussi in its multiple chambered phragmocone and suture line are Cymatoceras subradiatus (D’ ORBIGNY, 1850) and Cymatoceras cenomanense ( SCHLÜTER, 1876) (actually a synonym of the former, Frank et al. in prep). These species have a similar suture line with shallow ventral saddle, but the position of the siphuncle is central – dorso-central.

C. reussi may also be considered a juvenile specimen of Cymatoceras patens ( KNER, 1848) reported from the Maastrichtian due to its similar suture line with shallow ventral lobe and similar siphuncle position which is slightly above the centre in early ontogeny and centro-ventral in late ontogeny. This species features specific ribbing consisting of flattened lamellae with sharp edges in later ontogenic stages and a compressed shell with trapezoidal whorl cross section. Unfortunately, there are no preserved early juvenile specimens of C. patens to compare with C. reussi . However, the occurrences of the species are considerably distant in their stratigraphical position.

Until later ontogenetic stages, essential for comparison with other Late Cretaceous nautilids, are found, C. reussi should be kept as a valid taxon.

O c c u r r e n c e: Vinařice, Lower Coniacian, the Czech

Republic.