Sphenoceramus subcardissoides ( Schlüter, 1877 )

Landman, Neil H., Plint, A. Guy & Walaszczyk, Ireneusz, 2017, Allostratigraphy And Biostratigraphy Of The Upper Cretaceous (Coniacian-Santonian) Western Canada Foreland Basin, Bulletin of the American Museum of Natural History 2017 (414), pp. 1-173 : 93-94

Sphenoceramus subcardissoides ( Schlüter, 1877)

Figure 21

1877. Inoceramus subcardissoides Schlüter : 271, pl. 37

1905. Inoceramus subcardissoides Schlüter. Wegner : 169

1926. Inoceramus subcardissoides Schlüter. Heinz : 101

1932. Inoceramus subcardissoides Schlüter. Heinz : 24.

1953. Inoceramus subcardissoides Schlüter. Ødum : 12

1956. Inoceramus ex gr. subcardissoides Schlüter. Soukup : pl. 13, figs. 1–3.

1958. Inoceramus subcardissoides Schlüter. Kotsubinsky : 16, pl. 5, fig. 24.

1968. Inoceramus subcardissoides Schlüter. Kotsubinsky : 137, pl. 24, fig. 3.

non 1969. Inoceramus subcardissoides soukupi Mitura in Mitura et al.: 175, pl. 2, fig. 1

1974. Inoceramus cf. subcardissoides Schlüter. Tröger : pl. 6, figs. X4307, 4308

1991. Inoceramus subcardissoides Schlüter. Tröger and Christensen : 32, pl. 2, fig. 4.

pars 2001. Euryceramus cardissoides (Goldfuss) . Collom: 489, pl. 13, fig. 5; pl. 14, figs. 1–2 [non pl. 13, fig. 6]

LECTOTYPE: The original to Schlüter (1877: pl. 37), from the Emchermergel of the rock-waste deposit of the Carnap I Mine Shaft near Horst in Westphalia , northern Germany.

MATERIAL: Seven specimens in total. Two fragments, TMP 2016.041.0443 from 92.5 m and TMP 2016.041.0444 from 92.0 m from Bighorn Dam. One fragmentary specimen, TMP 2016.041.0235 from 100.3 m in West Thistle Creek. Incomplete huge specimen TMP 2016.041.0201 from 96.5 m in Chungo Creek. One large incomplete specimen (internal and outer mold of the same), TMP 2016.041.0001, and TMP 2016.041.0002, from 132 m of Ram River. Incomplete fragment, TMP 2016.041.0338 from Sheep River.

DESCRIPTION: The best preserved is TMP 2016.041.0001 (fig. 21), the large fragmentary specimen from the Ram River section (and TMP 2016.041.0002, its outer mold). It is the medium stage part of the RV, with h = 190 mm. Its juvenile and the anterior parts are missing. Also, it is slightly deformed in the preserved anterior part. The disc is wide, moderately inflated, apparently triangular in outline, covered with widely spaced, round-topped rugae and strong radial ribs. The latter weaken when crossing concentric rugae to form weakly developed nodes. The specimen retained a well-preserved radial sulcus, which is relatively broad and deep in the posterior part of the disc. The posterior auricle is not preserved. The radial ornament disappears from the radial sulcus, and reappears on the disc, posterior to the sulcus.

TMP 2016.041.0235, from Thistle Creek, represents a much younger stage of the LV. It shows well, however, the tripartite disc and, although weak, clearly developed radial ribs.

TMP 2016.041.0444, from Bighorn Dam, is a juvenile stage, 75 mm h long fragment. The specimen does not have radial ornament yet, which appears later in ontogeny. The outline and structure of the disc fits the characteristics of the species.

DISCUSSION: Although incomplete, our specimens show well the characteristics of Schlüter’s species: the presence of the strong, broad radial sulcus in the posterior part of the disc and the radial ornament, which crosses the concentric rugae, forming more or less well-developed nodes at crossings.

The best reported specimens, besides the illustrated type, are the ones photographed by Collom (2001: pl. 13, fig. 5; pl. 14), from the upper Coniacian of the Smoky River area. His specimen from the Puskwaskau Formation ( Collom, 2001: pl. 13, fig. 6) has different ornament and character of the posterior auricle, and is a different species.

OCCURRENCE: Sphenoceramus subcardissoides first appears apparently at the base of the upper Coniacian ( Tröger, 1989; Tröger and Christensen, 1991; Walaszczyk and Wood in Niebuhr et al., 1999). Heinz (1926) and Kotsubinsky (1958, 1968) reported the species from the upper Coniacian (upper Involutus Schichten in Heinz, 1926). Although quoted sometimes as ranging into the Santonian; no definite occurrence from this level can be confirmed. Consequently, it may be regarded as of late Coniacian age. In the studied area the species is common at the base of its range; its record higher in the succession is poorly known.

Figures

FIG. 21. Sphenoceramus subcardissoides (Schlüter, 1877), Wapiabi Formation, TMP 2016.041.0001, Ram River, 132 m, lateral view. The photograph is ×1.