Dalecarlioceras dalecarlicum ( Frye, 1987 ), 2013

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 24

Dalecarlioceras dalecarlicum ( Frye, 1987) comb. nov.

Fig. 7B

Cyrtorizoceras dalecarlicum Frye, 1987: 88 , 89, fig. 6d-f.

Emended diagnosis

Dalecarlioceras with slightly curved adult body chamber, with maximum adult height/width of ca. 40/ 38 mm, and adult peristome height/width 37/33.

Holotype

PMU 24774 .

Type locality and horizon

Kallholn, Siljan District, Sweden, Boda Limestone, Boda Core Member, late Katian, Ordovician.

Other material examined

One specimen ( PMU 24775 ) from Kallholn, Dalarna; one specimen from Rättvik, Dalarna, NRM Mo 150043, Boda Limestone, Boda Core Member, late Katian.

Description

See Frye (1987: 88-89) for a detailed description.

Remarks

Dalecarlioceras is endemic to the Boda Limestone. Originally, two species were assigned to this genus: the large D. bodense , characterized by a high angle of expansion, and the somewhat smaller, more slender D. constrictum Frye, 1987 ( Fig. 7A ). Herein, the medium sized Cyrtorizoceras dalecarlicum Frye, 1987 is considered an additional species of Dalecarlioceras . Dalecarlioceras dalecarlicum ( Frye, 1987) comb. nov. has an only slightly curved adult body chamber, combined with a slightly irregularly spaced ornamentation with transverse growth lines similar to those of D. bodense . The mature body chamber of D. dalecarlicum comb. nov. differs from that of Cyrtorizoceras in having a nearly straight, or slightly concave outline in lateral view ( Fig. 7 B-C); it is clearly compressed at the aperture in frontal view. Consequently, the body chamber of D. dalecarlicum comb. nov. is widest approximately at mid-length, like in D. bodense . D. dalecarlicum comb. nov. is considered to represent a transitional form between D. constrictum and Cyrtorizoceras thorslundi sp. nov. Together these forms represent a transition from the relatively small and slender C. thorslundi sp. nov., with a weakly gibbous body chamber, toward the massive, and strongly gibbous D. bodense . This suggests an ancestry or close relationship of Dalecarlioceras to Cyrtorizoceras .

Stratigraphic and geographic range

Boda Limestone, Dalarna, Sweden; late Katian.

Figures

Fig. 7. Breviconic cephalopods of the Boda Limestone and details of an endocerid. A. Dalecarlioceras constrictum Frye, 1987, PMU 24777, holotype, Kallholn. B. Dalecarlioceras dalecarlicum (Frye, 1987) comb. nov., PMU 24774, holotype, Kallholn. C. Cyrtorizoceras thorslundi sp. nov., PMU 26658, Kallholn; note the morphological transition between D. constrictum and C. thorslundi sp. nov.; the adult size increases in Dalecarlioceras and the mature body chamber is gibbous. D. Cameroceras turrisoides sp. nov., PMU 26623, Osmundberget, lateral view of apical fragment with abrupt transition between embryonic and juvenile conch. E. Strandoceras sphinx (Schmidt, 1858), PMU 26629, Kallholn. Scale bars: A-C, E = 10 mm; D = 10 mm.