Kiaeroceras heroyense Strand, 1934

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 14-15

Kiaeroceras heroyense Strand, 1934

Fig. 8 B-C

Kiaeroceras herØyense Strand, 1934: 99 , pl. 9, fig. 5.

Kiaeroceras heroyense – Flower in Flower & Teichert 1957: 60, text-fig. 17c.

Diagnosis

Kiaeroceras with strongly compressed conch cross section with width/height ratio of ca. 0.8. (Adopted from Strand 1934.)

Type locality and horizon

Herøya, near Porsgrunn, Norway; Herøya Formation (“Gastropod Limestone”), late Katian, Late Ordovician.

Material examined

PMU 26628 from Kallholn, Dalarna, Sweden; Boda Limestone, Upper Boda Member, Hirnantian, Late Ordovician.

Description

The specimen is a fragment of parts of the phragmocone and the body chamber of a mature individual ( Fig. 8B, C ). The conch is straight with a compressed cross section. At the base of the body chamber the maximum diameter is reached, with a height of 68 mm and a width of 55 mm (width/height ratio 0.81). At a position ca. 40 mm in apical direction, the conch height is 55 mm (angle of expansion, 18°). The preserved part of the body chamber is ca. 50 mm long. The conch surface is smooth with faint growth lines. The outer shell is relatively thick with ca. 1.5 mm at the base of the body chamber. The sutures form shallow lateral lobes, their distance is ca. 7 mm where the conch height is 60 mm (0.12 of corresponding conch height). The septa are shallowly convex with convexity of ca. 0.1 of corresponding conch height. The siphuncle is marginal with a diameter of ca. 0.15 of the corresponding conch cross section. The siphuncular segments are strongly expanded within the chambers.

Remarks

The specimen from the Boda Limestone is nearly identical in dimensions, septal convexity and chamber spacing to Kiaeroceras frognoyense Strand, 1934 . However, Strand (1934) distinguished the two species of Kiaeroceras based on the shape of the conch cross section. As the width/height ratio of the conch of specimen PMU 26628 is 0.81, it is more similar to K. heroyense than to K. frognoyense (with a width/ height ratio of 0.87), with a less compressed conch ( Strand 1934: 97).

Kiaeroceras frognoyense and K. heroyense probably represent a continuous spectrum of morphological variation or sexual dimorphs. Given the paucity of known material, such speculation cannot be tested and the original species diagnoses of Strand (1934) are accepted herein.

The specimen, described above, is the most complete specimen known from this genus with regard to the phragmocone. It displays a curved lateral outline of both the pro- and antisiphuncular conch margin, an oval conch cross section and details of the shell surface.

Stratigraphic and geographic range

Herøya Formation, Norway ( Strand 1934); Boda Limestone, Upper Boda Member, Hirnantian, Dalarna, Sweden; all late Katian-Hirnantian.

Figures

Fig. 8. Orthoconic brevicones of the Boda Limestone of Kallholn. A. Tyrioceras cf. kjaerulfi Strand, 1934, PMU 26897, view from antisiphuncular side. B-C. Kiaeroceras heroyense Strand, 1934, PMU 26628. B. Lateral view, with siphuncle on left side. C. View from antisiphuncular side. Scale bar = 10 mm for all figures.