Kallholnoceras sp.

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 : 77-78

Kallholnoceras sp.

Fig. 27G–H

Material examined

ESTONIA • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; TUG 1745-4 • 1 spec.; Vormsi Island , Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 878-323 • 1 spec.; Vohilaid Island , Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-233 .

Description

Specimen GIT 878-233 (Fig. 27H) is a fragment of a mature body chamber with a height and width of 33 mm and 20 mm, respectively (CHI = 1.65). The preserved length of the body chamber is 28 mm. The body chamber is slightly exogastrically curved and slightly gibbous. An inconspicuous constriction occurs near the adoral margin of the preserved part where the conch height is ca 30 mm.

The second specimen (GIT 878-323) preserves parts of a mature body chamber and three chambers of the phragmocone (Fig. 27G). The conch height at the base of the body chamber was estimated ca 33 mm. The body chamber is similar in shape and preserved height to that of specimen GIT 878-233. The preserved part of the phragmocone indicates a relatively strong exogastric conch curvature. The third specimen (TUG 1745-4) is a strongly curved fragment of a phragmocone of seven chambers with a maximum conch height of 26 mm.

Remarks

The two specimens belong to a strongly curved, compressed oncocerid species with a gibbous body chamber. Their general conch shape is similar to that of Kallholnoceras . All three specimens are larger than the type species of this monotypic genus, which has a mature conch of 20 mm. Because of the fragmentary character of the material, a species level determination, and the erection of a new species is not currently possible.

Family Oncoceratidae Hyatt, 1884