Tyrioceras warburgae Frye, 1982

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 68-71

Tyrioceras warburgae Frye, 1982

Fig. 29B

Tyrioceras warburgae Frye, 1982: 1282 , pl. 2, figs 5-7, text-fig.5.

Emended diagnosis

Tyrioceras with angle of expansion of 12–15°, with slightly depressed to slightly compressed conch cross section; ornamented with marked sinuous transverse growth lines that form ventral, lateral and dorsal sinuses, and relatively deep ventrolateral and dorsolateral salients.

Type locality and horizon

Kallholn, Siljan district, Dalarna, Sweden; Boda Limestone, late Katian, Ordovician.

Material examined

Eleven specimens in total: three specimens ( PMU 26898–26900), the holotype ( PMU 24747) and five paratypes ( PMU 24748–24752), all from Kallholn; two specimens from Unskarsheden ( PMU 26901, 26902), Siljan district, Dalarna, Sweden; Boda Limestone, latest Katian, Ordovician.

Description

Frye (1982) described the ornamentation of this species in detail. Additional new details of the conch shape and internal characters are described herein.

The holotype is a 67 mm long portion of phragmocone with a circular diameter at conch cross sections increasing from 28 to 46 mm, with an angle of expansion of 15°. In two of the paratypes (PMU 24748, 24750), width/height ratios are 0.94 (at width 32 mm), 0.93 (at width 25 mm) and 0.94 (at width 75 mm), respectively.

Specimen PMU 26900 is a 65 mm long portion of a phragmocone with a conch height increasing from 34 to 47 mm (angle of expansion 11.3°). The conch cross section is slightly elliptically depressed, with a width/height ratio of 1.10. The sutures are directly transverse, with a distance between two septa equal to ca. 0.4 of the conch height. The siphuncle is slightly eccentric, with a SPR of 0.43 and a diameter of 0.17 of the conch cross section. The connecting ring is not preserved. The septal necks are 6 mm long and orthochoanitic to suborthochoanitic. On the prosiphuncular side, the chambers are filled with heavy epi-, and hyposeptal and mural deposits, which are partially fused. The hyposeptal deposits cover the entire adapical/external surface of the septal neck ( Fig. 29B ).

Remarks

Frye (1982) did not include the shape of the cross section in the original diagnosis of this species. The conch cross section of the holotype is circular. Additionally, there are specimens with slightly compressed to slightly depressed conch cross section, which are identical to the type in all other features. The relatively low number of specimens in the collection does not allow for a proper evaluation of this character for classification purposes. Here, the variability in conch cross section is interpreted as intraspecific and the species diagnosis is emended accordingly.

Comparison

Tyrioceras kiaerulfi differs from T. warburgae in having a compressed conch cross section for its known length and generally in having a lower angle of expansion.

Stratigraphic and geographic range

Boda Limestone, late Katian, Dalarna, Sweden.

Figures

Fig. 29. Polished median sections of Tyrioceras Strand, 1934, Boda Limestone. A. Tyrioceras cf. kjaerulfi Strand, 1934, PMU 26897, Kallholn, detail of septal neck with massive endocameral and epichoanitic deposits and long orthochoanitic septal necks. B. Tyrioceras warburgae Frye, 1982, PMU 26900, Kallholn, detail of septal neck with epichoanitic deposits. C. Same specimen as in A, total fragment. Scale bars: A-B = 5 mm; C = 10 mm.