Dowlingoceras tornense, Kröger, 2025

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 : 71-72

Dowlingoceras tornense sp. nov.

urn:lsid:zoobank.org:act:9E94767A-9B7E-440B-84D7-12F695042F30

Figs 25A–B , 27I

Diagnosis

Dowlingoceras with compressed elliptical conch-cross section (CHI = 1.3); mature body chamber with maximum conch height of ca 45 mm near its base and height to length ratio of ca 1, with a nearly straight, simple peristome and apparently lacking or only with a very shallow hyponomic sinus; angle of expansion of the phragmocone ca 12°.

Etymology

The Estonian “ torni ”, ‘towerʼ, refers to the type locality.

Type material

Holotype

ESTONIA • Vormsi Island , Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 840-254 .

Paratype

ESTONIA • same data as for holotype; GIT 840-273 .

Description

The holotype preserves parts the phragmocone and the mature body chamber. Where preserved (near the peristome), the conch surface is apparently smooth. The conch height and width at the base of the mature body chamber are 45 mm and 34 mm, respectively (CHI = 1.3). There, the shape of conch cross section is apparently elliptically to oval compressed. The ventral side is slightly more narrowly curved. In lateral view, the conch is straight. The body chamber is 46 mm long with a nearly straight, simple peristome and apparently without a hyponomic sinus. The lateral outline of the body chamber is slightly convex, reaching the greatest conch height 47 mm at ca mid-length location of the body chamber.

The phragmocone increases in height from 38 mm to 45 mm at a length of 32 mm (angle of expansion = 12°). The sutures form a shallow lobe at the lateral sides of the phragmocone, a sharp saddle on the ventral side and a rounded saddle on the dorsal side; they are 8 mm apart where the conch height is 42 mm (RCL = 0.19). The septal foramen is nearly marginal with a diameter of 5 mm where the conch height is 43 mm (RSH = 0.12). A natural cut of the siphuncle shows a fusiform, elongated, Dowlingoceras -like siphuncular segments (length 6 mm, height 3.8 mm, SCR = 0.63).

Comparison

The conch shape, including the shape of the mature body chamber is similar to that of D. kallholnense Frye, 1987 . However, the mature body chamber of D. tornense sp. nov. is greater in height, width, and length than that of D. kallholnense (40 mm, 36 mm, 40 mm, respectively, in D. kallholnense ) and the conch cross section is more compressed (CHI = 1.1 in D. kallholnense ).

Figures

Fig. 25. Diestoceratids from the Pirgu Regional Stage, Estonia. A–B. Dowlingoceras tornense sp. nov., paratype GIT 840-273, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. A. Lateral view, prosiphuncular side left. B. View of the prosiphuncular side. C. Danoceras piersalense (Teichert, 1930) comb. nov., specimen GIT 878-263, from Hosholm shore (tower), Vormsi Island. Scale bar = 10 mm, same scale in all figures.