Ruthenoceras elongatum Korde, 1949

Dzik, Jerzy, 2020, Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia, Acta Palaeontologica Polonica 65 (1), pp. 149-165 : 163

Ruthenoceras elongatum Korde, 1949

Fig. 13 .

Holotype: The only specimen available to Korde (1949) was a phragmocone in a petrographic thin section ( Korde 1949: fig. 1); its repository was not specified but it is likely the Paleontological Institute of the Russian Academy of Sciences, Moscow.

Type locality: Angara River shore 4 km from the former village Boguchany near the Kodinsk dam on the Angara River.

Type horizon: Stromatolitic limestone of the Ust-kut Formation, probably latest Furongian.

Material.— 146 specimens collected from a loose block of stromatolitic limestone at the shore of Angara River at the former village Pashino near Kodinsk .

Diagnosis.—As for the genus.

Remarks. — Balashov (1962) based his Clarkoceras angarense on seven specimens collected by V.P. Maslov in 1952 at his exposure 236 and by K.G. Ginsburg 1955 in 1955 at his exposure 55, probably from the upper Ust-Kut Formation on the left bank of Angara, 1.2 km downstream of Pashennaya Kochegda and from the right bank of Angara downstream of the Bryansk constriction. Some of the three specimens from the Chunya river collected by G.F. Lungershausen in 1949 were also illustrated. The holotype consists of an incomplete living chamber bent near the base and the proximal portion of its gently curved phragmocone showing a change from only slightly to strongly oblique septa. The three paratypes exhibit even more oblique septa. All those specimens are laterally compressed and they are virtually straight. Another paratype shows a conch with a curvature increase near the apex and towards the living chamber base ( Balashov 1962: pl. 5: 10). Balashov’s (1962) material fits the modal morphology of the ellesmeroceratid from Pashino and little doubt remains that they are conspecific. No other species shows a similar disposition of septa and shape of the conch.

Figures

Fig. 13. Restoration of the conch of Ruthenoceras elongatum Korde, 1949 from the Ust-kut Formation of Siberia, with hypothetical subspherical apex based mostly on ZPAL N. IV/4 (Fig. 5A). A. Septum in proximal view. B. Conch in lateral view with the body and proximal part of sipho exposed. C. The body and a portion of sipho in dorsal view.