Tyrioceras cf. kjaerulfi Strand, 1934

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 68

Tyrioceras cf. kjaerulfi Strand, 1934

Figs 8A , 10B , 29A, C , 30

Tyrioceras kjaerulfi Strand, 1934: 50 , pl. 6.

Tyrioceras kjerulfi – Dzik 1984: 133, 138, text-fig. 55.5.

Diagnosis

Tyrioceras with angle of expansion of 11°; compressed conch cross section; ornamented with marked sinuous transverse growth lines that form ventral, lateral, and dorsal sinuses, and relatively deep ventrolateral and dorsolateral salients. (Adopted from Strand 1934.)

Type locality and horizon

Furuholmen, Asker District, Norway, Grimsøy Formation (questionable), late Katian, Late Ordovician.

Material

One specimen from Kallholn, PMU 26897, Siljan district, Dalarna, Sweden; Boda Limestone, Boda Core Member, late Katian, Ordovician.

Description

Specimen PMU 26897 is a portion of a phragmocone 56 mm long with conch height and width increasing from 27 to 41 mm and 25 to 34 mm, respectively. The angles of expansion are 14° and ca. 9°, respectively, whereas the width/height ratio decreases from 0.93 apically to 0.83 adorally ( Figs 8A , 10B ). The relative chamber height is 0.4, and the septal convexity is 0.25 of the corresponding conch height. The siphuncle is subcentrally positioned with a diameter of ca. 0.13 of the conch cross section. The connecting ring is not preserved, but the septal necks are orthochoanitic and relatively long with ca. 0.45 of the chamber height ( Fig. 29A, C ). Heavy epi-, hyposeptal and mural deposits are developed. Adapically, the deposits cover the apical septal necks, forming epichoanitic deposits ( Fig. 30 ).

The conch surface is ornamented with transverse lirae, ca. 4–5 in a distance of 1 mm. The spacing of the lirae varies periodically, forming bands with widths of ca. 4 mm. The lirae form a shallow sinus on the prosiphuncular, and a more pronounced sinus on the antisiphuncular side of the conch.

Remarks

This species is based on a single, probably mature body chamber fragment only. Nothing is known about the ontogenetic and intraspecific variability of characters such as angle of expansion, conch cross section or ornamentation. The specimen PMU 26897, described above, is similar to Tyrioceras kjaerulfi with respect to the compressed conch cross section and the irregularly spaced transverse ornamentation. However, the type of the species differs in having a comparatively low angle of expansion (11°) and a lower width/height ratio (0.79). The specimens are provisionally interpreted as conspecific.

Stratigraphic and geographic range

Grimsøy Formation (questionable), Asker District, Norway; Boda Limestone, Dalarna, Sweden, all late Katian, Late Ordovician.

Figures

Fig. 8. Orthoconic brevicones of the Boda Limestone of Kallholn. A. Tyrioceras cf. kjaerulfi Strand, 1934, PMU 26897, view from antisiphuncular side. B-C. Kiaeroceras heroyense Strand, 1934, PMU 26628. B. Lateral view, with siphuncle on left side. C. View from antisiphuncular side. Scale bar = 10 mm for all figures.

Fig. 10. Camera lucida drawings of cross sections of selected Boda Limestone cephalopods. A. Cyrtorizoceras thorslundi sp. nov., PMU 26657, Osmundsberget, mature body chamber. B. Tyrioceras cf. kjaerulfi Strand, 1934, PMU 26897, Kallholn. C. Nathorstoceras adnatum sp. nov., PMU 26733, holotype, Kallholn. D. Nathorstoceras kallholnense sp. nov., PMU 26729, holotype. E. Redpathoceras depressum sp. nov., PMU 26927, holotype, Kallholn, cross section of base of mature truncated conch. F. Schuchertoceras fryi sp. nov., PMU 24744, holotype, Kalllholn, cross section of mature aperture (dark grey) and body chamber (medium grey). G. Redpathoceras bullatum sp. nov., PMU 26923, holotype, Kallholn, cross section of base of mature truncated conch. Prosiphuncular side directed downward in all figures. Siphuncles shown as white circles. Scale bar = 10 mm for all figures.

Fig. 29. Polished median sections of Tyrioceras Strand, 1934, Boda Limestone. A. Tyrioceras cf. kjaerulfi Strand, 1934, PMU 26897, Kallholn, detail of septal neck with massive endocameral and epichoanitic deposits and long orthochoanitic septal necks. B. Tyrioceras warburgae Frye, 1982, PMU 26900, Kallholn, detail of septal neck with epichoanitic deposits. C. Same specimen as in A, total fragment. Scale bars: A-B = 5 mm; C = 10 mm.

Fig. 30. Reconstruction of median section of Tyrioceras cf. kjaerulfi Strand, 1934, PMU 26897, Boda Limestone, Kallholn. Black = outer shell and septa; grey = cameral deposits.