Piersaloceras (?) sp., Teichert, 1930

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 : 76-77

Piersaloceras (?) sp.

Figs 30C , 31A

Material examined

ESTONIA • Sutlema old quarry; Kõrgessaare Formation , Vormsi Regional Stage; TUG 1827-163 .

Description

The specimen is a fragment of a curved body chamber, preserved in its total length but lateral parts of the body chamber are missing ( Fig. 30C ). The outer shell is well-preserved, it is ornamented with narrowly spaced (ca 15–20 per 10 mm) imbricated frills ( Fig. 31A ), which are directly transverse, and parallel to the peristome. No hyponomic sinus occurs. In lateral view, both margins are curved. The curvature of the concave margin is wider than that of the convex margin, which results in a gibbous outline of the body chamber. The greatest conch height of 50 mm is located at ca mid-length of the body chamber. At its base, the height is 48 mm and at the aperture 43 mm. The suture, reconstructed from the base of the body chamber, forms a narrow lateral lobe. No traces of the siphuncle and of the septal foramen are preserved.

Remarks

The characteristically frilled ornamentation of this fragment is most similar to that of P. gageli Teichert, 1930 , which, in turn, is known only from a single, immature specimen. It differs from the type specimen (and, to date, only known specimen of this genus) in lacking the longitudinal furrows on the impression of the mold, which could be an effect of the typical oncoceratid longitudinal ridges, and which is present in more apical conch parts of many oncocerids (see discussion in Frye 1987: 92). Because details of the siphuncle and parts of the phragmocone are unknown from the specimen described above, a definite determination is not possible. The general shape of the body chamber is similar to that of Redpathoceras saxbyense sp. nov., and to Uranoceratidae , such as Deckeroceras Foerste, 1935b . The mature body chamber of the former is however longer (68 mm) and at its base less high (45 mm). More complete, better-preserved material is needed to evaluate the relationship of this specimen to Redpathoceras , or whether Piersaloceras might belong to the Uranoceratidae or Probillingsitidae Flower, 1941 .

Notably, some oncoceratids, such as Beloitoceras or Neumatoceras also have similarly shaped body chambers, but are more strongly compressed and have a hyponomic sinus. This could link oncoceratids and uranoceratids, as suggested by the phylogeny in Pohle et al. (2022).

Figures

Fig. 30. Graciloceratidae Flower, 1950 and Oncoceratidae Hyatt, 1884 of the Vormsi–Pirgu regional stages, Estonia. A. Beloitoceras siljanense Frye, 1987, specimen TUG 939-56 from Haapsalu holm, Pirgu Regional Stage, lateral view. B. Rizosceras teres sp. nov., paratype GIT 426-550, from Kõrgessaare quarry, Vormsi Regional Stage, lateral view. C. Piersaloceras (?) sp., specimen TUG 1827-163, from Sutlema old quarry, Vormsi Regional Stage, lateral view. Scale bar = 20 mm, same scale in all figures.

Fig. 31. Details of shell ornamentation of cephalopods of the Vormsi–Pirgu regional stages, Estonia. A. Piersaloceras (?) sp., specimen TUG 1827-163, from Sutlema old quarry, Vormsi Regional Stage. B. Kiaeroceras urgense sp. nov. holotype TUG 103-75, from Urge quarry, Vormsi Regional Stage. C–D. Strandoceras sphynx (Schmidt, 1858). C. Specimen TAM G432:68, from Niibi hillock, Pirgu Regional Stage. D. Specimen TUG 1672-29, from Saxby village, Pirgu Regional Stage. E. Strandoceras sulevipoegi sp. nov., paratype TUG 899-55, from Saxby shore, Vormsi Regional Stage. Scale bar = 5 mm in all figures, same scale in A–B, and in C–E.