Dalecarlioceras constrictum 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 : 86-88

Dalecarlioceras constrictum Frye, 1987

Figs 29D , 34A–B

Dalecarlioceras constrictum Frye, 1987: 92–93 , fig. 3g –h.

Dalecarlioceras constrictum – Kröger 2013: 24, fig. 7a, tab.2.

Diagnosis

Moderately expanding Dalecarlioceras with curved, relatively short conch and compressed conch cross section; mature body chamber gibbous with maximum conch height of ca 44 mm, not greatly inflated; mature aperture constricted apicad of peristome, aperture height is one-fourth of body chamber length; peristome with well-developed hyponomic sinus. (Adopted from Frye 1987.)

Material examined

ESTONIA • 2 specs; Vormsi Island, Hosholm shore (tower); Adila Formation, Pirgu Regional Stage; GIT 878-248, GIT 878-251.

Type locality and horizon

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

Description

Specimen GIT 878-248 is a fragment of a mature body chamber and three chambers of the phragmocone. The conch surface is poorly preserved. Near the peristome, it is almost smooth with fine, irregularly spaced growth lines. At the base of the body chamber, the conch height and widths are 41 mm and 35 mm, respectively (CHI = 1.1). The body chamber is gibbous, 35 mm long, and in lateral view has convex outlines with the greatest conch height of 44 mm 20 mm adoral of the base of the body chamber. The phragmocone increases in height from 40 mm to 34 mm at a length of 18 mm (angle of expansion = 19°). The sutures form shallow lateral lobes and are 6 mm apart where the conch height is 38 mm (RCL = 0.16). The siphuncle is nearly marginal, has fusiform segments and is without endosiphuncular deposits. The septal necks are suborthochoanitic to cyrtochoanitic ( Fig. 29D ).

In GIT 878-251, a nearly complete mature body chamber and seven chambers of the phragmocone are preserved ( Fig. 34A–B ). At its base the body chamber is 37 mm high, and 34 mm wide (CHI = 1.1), has a broad elliptical conch cross section, and a gibbous form in lateral view. The greatest height is reached ca 20 mm adorad from its base (ca 44 mm), its total length is 43 mm. The mature peristome has a ca 7 mm deep, wide hyponomic sinus developed on the prosiphuncular side. The height of the phragmocone increases from 27 mm to 37 mm at a length of 31 mm (angle of expansion 18°). The siphuncle is located near the conch margin, its segments are fusiform (siphuncular height = 3.2 mm, segment length = 5.5 mm).

Remarks

The species was described in detail by Frye (1987). The Estonian specimens are very similar to the Swedish types.

Figures

Fig. 29. Median sections of phragmocones of Graciloceratidae Flower, 1950 and Oncoceratidae Hyatt, 1884 of the Vormsi–Pirgu regional stages, Estonia. A. Hiiumoceras hiiuense gen et sp. nov., holotype TUG 1745-11, from Paope quarry, Hiiumaa Island, Vormsi Regional Stage. B. Rizosceras teres sp. nov., paratype TUG 80-508, from Saxby shore, Vormsi Island, Vormsi Regional Stage. C. Beloitoceras siljanense Frye, 1987, specimen TUG 939-56, from Haapsalu holm, Pirgu Regional Stage. D. Dalecarlioceras constrictum Frye, 1987, specimen GIT 878-248, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. Scale bars = 5 mm.

Fig. 34. Dalecarlioceras Frye, 1987 of the Vormsi–Pirgu regional stages, Estonia. A–B. Dalecarlioceras constrictum Frye, 1987, specimen GIT 878-251, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. A. View of the prosiphuncular side. B. Lateral view. C. Dalecarlioceras sp., specimen GIT 878-250, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage, lateral view. D–F. Dalecarlioceras bodense Frye, 1987, specimen TUG 1745-213, from Saaremõisa (Lyckholm), Vormsi Regional Stage. D. Adapical view. E. Lateral view. F. View of the antisiphuncular side. Scale bar = 20 mm in all figures, same scale in A–C, and in D–F.