Dowlingoceras kallholnense Frye, 1987

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 70-71

Dowlingoceras kallholnense Frye, 1987

Figs 16E, 27A

Dowlingoceras kallholnense Frye, 1987: 95–96 , figs 6a–b, 7.

Dowlingoceras kallholnense – Kröger 2013: tab.2.

Diagnosis

Dowlingoceras with a slightly compressed cross section (CHI = 1.1); oval cross section, venter narrower than dorsum; mature body chamber is more gibbous than those of the other species of the genus, ca 40 mm high at its base, and with marked constriction near the peristome. (Compiled from Frye 1987.)

Material examined

ESTONIA • Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 878-247.

Type locality and horizon

Kallholn, Dalarna, Sweden; Boda Formation, latest Katian.

Description

Specimen GIT 878-247 preserves parts of the mature body chamber and the phragmocone with a conch height and width of 39 mm and 32 mm, respectively (CHI = 1.2) The conch cross section is oval with a narrower curvature on the ventral compared to the dorsal side. The conch height increases from 36– 37 mm at a length of 17 mm (angle of expansion 8°). The body chamber is only partly preserved, had a length of more than 38 mm and decreases in conch height from its base with a convex outline in lateral view toward ca 35 mm in height. The sutures form a wide lateral lobe and are ca 6 mm apart where the conch height is 39 mm (RCL = 0.15). The siphuncular segments are elongated (7 mm long, 4 mm high, SCR = 0.57) fusiform, wider adorally and adnate to the adoral septal surfaces. The septal necks are poorly preserved, apparently cyrtochoanitic.

Remarks

The Swedish types of D. kallholnense have conch dimensions (maximum height of mature body chamber = 40 mm; CHI = 1.1, and a low angle of expansion in the adoral parts of the phragmocone) ( Frye 1987) which are nearly identical to the specimen described herein. The differences in the connecting ring shape (presence of an adnate area in specimen GIT 878-247 are interpreted as taphonomic or the effects of orientation of the cut. (See also Turek & Aubrechtová 2024, and Pohle et al. 2024, on this topic.) The view is oblique to the dorso-ventral body axis, in Frye (1987: fig. 7), it is apparently perpendicular to that axis in specimen GIT 878-247 (Fig. 16E).