Palaeodawsonocerina senckenbergi ( Teichert, 1930 )

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 34-36

Palaeodawsonocerina senckenbergi ( Teichert, 1930)

Figs 12A , 18C

Spyroceras senckenbergi Teichert, 1930: 280 , pl. 5, figs 3, 4.

Palaeodawsonocerina senckenbergi – Kröger & Isakar 2006: 154, figs 8a, 10i, 12d-e, 12h (with synonymy).

non Spyroceras senckenbergi – Dzik 1984: 122, 125, pl. 35, fig. 5, text-figs 48a, 49.20.

Diagnosis

Straight, slightly compressed conch with very low apical angle of approximately 1°–2°; adult dorsoventral diameter approximately 25 mm; with five to six annulations at a distance that equates to the corresponding shell diameter in adult specimens; annulations straight or very slightly oblique toward the growth direction and regularly spaced; very fine growth lines, about 50 in a cycle of annulation; very fine longitudinal striae or raised lines, about five to seven per millimetre; suture line follows the ridges of the annulations; siphuncle central, slightly expanded within the chambers; septal perforation about 0.07 of the shell diameter. (From Kröger & Isakar 2006.)

Type locality and horizon

Lyckholm, Estonia, “Lyckholm stage” of Teichert (1930), Vormsi/Pirgu Regional Stage, late Katian, Late Ordovician.

Material examined

Seven specimens ( PMU 26718–26724), Kallholn; two specimens ( PMU 26725–26726), Osmundsberget, Siljan District, Sweden; all Boda Limestone, Boda Core Member, late Katian, Late Ordovician.

Remarks

This species was described in detail by Kröger & Isakar (2006). The material from the Boda Limestone reveals information regarding the ornamentation. PMU 26718 reveals that the annuli are sharply crested and symmetrical in longitudinal cross section ( Figs 12A , 18C ). The longitudinal ornamentation consists of fine raised lirae, ca. 0.5 mm apart where the conch diameter is 16 mm. Additional, faint, directly transverse growth lines occur that are more pronounced in mature growth stages. The largest specimen from the Boda Limestone is 25 mm in diameter (PMU 26724) and supports an earlier assessment ( Kröger & Isakar 2006) that the diameter at maturity of individuals of this species is ca. 25 mm.

Stratigraphic and geographic range

Keila/Vormsi Regional Stages, Estonia ( Kröger & Isakar 2006); Boda Limestone, Siljan District, Sweden; Katian, Ordovician.

Figures

Fig. 12. Annelate Orthocerida of the Boda Limestone. A. Palaeodawsonocerina senckenbergi (Teichert, 1930), PMU 26718, Kallholn. B-C. Striatocycloceras isbergi sp. nov., Osmundsberget. B. PMU 26660, holotype, Osmundberget. C. PMU 26664. D-E. Palaeodawsonocerina? nicolletoides sp. nov., PMU 26728, Kallholn. D. Adapical view. E. Lateral view. Scale A-C = 10 mm; D-E = 10 mm.

Fig. 18. Shell ornamentation of selected Cephalopoda of the Boda Formation. A. Order, gen. et sp. indet., PMU 26950, Kallholn, lateral view. B. Palaeodawsonocerina? nicolletoides sp. nov., PMU 26727, holotype, Kallholn. C. Palaeodawsonocerina senckenbergi (Teichert, 1930), PMU 26718, Kallholn. D. Geisonoceras wegelini (Angelin in Angelin & Lindström, 1880) comb. nov., PMU 26745, Unskarsheden. E. Pleurorthoceras osmundsbergense sp. nov., NRM-PZ Mo 150126, holotype, Osmundsberget. F. Warburgoceras longitudinale (Angelin in Angelin & Lindström, 1880) comb. nov., NRM-PZ Mo 154065, Unskarsheden. G. Redpathoceras depressum sp. nov., PMU 26931, Kallholn. Scale bar = 5 mm for all figures.