Inoceramus gibbosus 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 : 63-64

Inoceramus gibbosus Schlüter, 1877

Figures 5C, D, G

1877. Inoceramus gibbosus Schlüter : 271.

1888. Inoceramus percostatus Müller : 413, pl. 17, fig. 3.

? non 1911. Inoceramus percostatus Müller. Andert : 56, pl. 5, fig. 4.

1929. Inoceramus dankeri Heinz var. anderti Heinz. Heinz : 686, figs. 4–5.

1929. Inoceramus gibbosus Schlüter. Heine : 50, pl. 4, figs. 20–22.

1929. Inoceramus percostatus Müller. Heine : 46, pl. 3, figs. 14–17.

1929. Inoceramus bilobatus Müller. Heine : 49, pl. 4, figs. 18–19.

? non 1934. Inoceramus percostatus Müller. Andert : 119, pl. 5, fig. 4.

1958. Inoceramus russiensis Nikitin. Bodylevski : 78, pl. 29, fig. 1; pl. 31, fig. 1.

1959. Inoceramus percostatus Müller. Drobrov and Pavlova : 145, pl. 12, fig. 3.

non 1963. Inoceramus percostatus Müller. Assmus : 45, pl. 9, fig. 1.

? non 1969. Inoceramus percostatus Müller. Khalafova : 177, pl. 13, fig. 4; pl. 14, fig. 1 [pl. 13, fig. 4 = deformis group; pl. 14, fig. 1 =? Tethyoceramus sp. ]

1972. Inoceramus percostatus Müller. Glazunova : 59, pl. 2, figs. 1–2; pl. 3, fig. 2; pl. 9, fig. 1, pl. 13, fig. 6.

1972. Inoceramus percostatus Müller subsp. gorenkaensis subsp. nov., Glazunova: 60, pl. 4, figs. 1–2; pl. 6, figs. 1–2; pl. 7, fig. 1; pl. 9, fig. 2.

2006. Inoceramus gibbosus Schlüter, 1877 . Walaszczyk and Cobban: 273; text-figs. 21, 12.11 and 13.5.

TYPE: The holotype, by monotypy, is the original of Schlüter (1877: 271) first illustrated by Heine (1929: pl. 4, figs. 20–22) from the upper Coniacian of Osterfeld Mine near Oberhausen, in Westphalia, northern Germany.

MATERIAL: Twenty-six specimens in total, most of which are fragmentarily preserved. TMP 2016.041.0110 through 2016.041.0127, from Blackstone River. TMP 2016.041.0236 from Thistle Creek. TMP 2016.041.0098, 2016.041.0089, 2016.041.0090, and 2016.041.0095, from Wapiabi Creek. TMP 2016.041.0170 and 2016.041.0172 from Chungo Creek. One unnumbered specimen from Sheep River.

MEASUREMENTS: See table 1.

DESCRIPTION AND REMARKS: Most of the specimens in our collection are small-sized, juvenile fragments from the Blackstone River section. They show, however, the upright form, pointed beak, and triangular outline, with well-developed, distinct rugae, covered with well-developed, sharp-edged growth lines, typical for the species.

The best preserved is specimen TMP 2016.041.0110 from Blackstone River; the major part of the adult stage is well preserved (fig. 5D). Its umbonal part is poorly preserved (deformed), as is its anterior part. The disc, within the preserved part, is subrectangular in outline, and possesses a distinct radial sulcus posteriorly of the growth axis. The sulcus is shallow and does not deform the concentric rugae. The concentric rugae are regular to subregular, symmetrical, with rounded edges. They are covered with sharpe-edged growth lines, which are evenly developed on the entire height of the disc.

The juvenile fragment from Sheep River (fig. 5C) possesses a well-preserved posterior auricle, which is extended and well separated from the disc, along a well-developed auricular sulcus. The disc is covered with subregular concentric rugae, superimposed by raised sharp-edged growth lines that are typical of the species.

The medium-sized incomplete specimen TMP 2016.041.0172 (fig. 5G), from Chungo Creek, demonstrates well the general outline of the species and type of ornament. The posterior part of its disc, with the posterior, radial sulcus, is deformed and partly missing.

OCCURRENCE: The species (as herein interpreted) is known from the Wapiabi Formation from localities on Blackstone River, Wapiabi Creek, West Thistle Creek, Sheep River, and Chungo Creek. It occurs invariably in the topmost part of the lower Coniacian, disappearing below the entry of the first Volviceramus . The species, as herein understood, was first precisely located in the stratigraphic succession of the Staffhorst Mine section, in northern Germany (Walaszczyk and Wood in Niebuhr et al., 1999), where it occurs in an equivalent stratigraphic interval. Although the species was also reported from other regions (e.g., eastern part of European Russia; see, e.g., Nikitin, 1888; Glazunova, 1972), precisely located specimens have not been reported.

Figures

FIG. 5. Stratigraphic ranges of Scaphites (S.) preventricosus, S. (S.) ventricosus, S. (S.) depressus, and Clioscaphites saxitonianus (plotted on the left side) next to a curve of the changes in relative sea level during the Turonian-Santonian based on analysis of stratigraphic sections in the Western Foreland Basin (Plint et al., this issue). The evolutionary relationships proposed by Cobban (1952) are presented as a cladogram showing the trend toward recoiling at maturity.