Cremnoceramus sp.

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 : 69-73

Cremnoceramus sp.

Figures 9, 10

MATERIAL: Forty-one specimens in total. Seven specimens from Chungo Creek: TMP 2016.041.0176 though to TMP 2016.041.0180 from 33.5 m; TMP 2016.041.0175 from 34.5 m; and TMP 2016.041.0174 from 37 m. Two specimens from West Thistle Creek; TMP 2016.041.0239 and TMP 2016.041.0237, both from 28.5 m. Nine specimens from Blackstone River: TMP 2016.041.0102 from 6.5 m; TMP 2016.041.0103 from 13.6 m; TMP 2016.041.0132 from 20.5 m; TMP 2016.041.0133 from 38.2 m; TMP 2016.041.0134 from 39.4 m; and TMP 2016.041.0128 through to TMP 2016.041.0131, from 43.5 m. Four specimens from Wapiabi Creek: TMP 2016.041.0096 from 2.8 m; TMP 2016.041.0101 from 7.9 m; TMP 2016.041.0100 from 48.5 m; and TMP 2016.041.0089 from 54.7 m. Six specimens from Sullivan Creek: TMP 2016.041.0078 through to TMP 2016.041.0083, from the inconstans interval. Single, unnumbered specimen from Cutpick Creek. Eight specimens from Bighorn Dam: TMP 2016.041.0389 through to TMP 2016.041.0394 from 8.5 m; TMP 2016.041.0397 from 10.5 m; TMP 2016.041.0401 from 32.5 m; and TMP 2016.041.0396 from 34.0 can Western Interior) ( Tröger, 1981, 1989; m. Four specimens from Highwood River: TMP Walaszczyk, 1992; Kauffman et al., 1993; 2016.041.0141, TMP 2016.041.0142, TMP Walaszczyk et al., 1998; Walaszczyk and Cobban, 2016.041.0143, and TMP 2016.041.0146. 1998, 2000; Wood et al., 2004); North Pacific REMARKS: The taxonomy and evolutionary Province ( Japan, Sakhalin) ( Noda, 1996), New interpretation of the genus, as applied herein, Zealand ( Crampton, 1996), South America (Brafollows Walaszczyk and Wood (1998) and zil) ( Kauffman and Bengtson, 1985).

Walaszczyk and Cobban (2000), with slight modification, as discussed below.

Volviceramus Stoliczka, 1871

The genus is well represented in the lowermost part of the Wapiabi Formation, up to sur- TYPE SPECIES: Inoceramus involutus J. de C. face CS4. The cremnoceramid assemblage is Sowerby: 1828: 160, pl. 583, figs. 1–3, by original composed of Cremnoceramus deformis deformis designation ( Stoliczka, 1871: 394, 401).

( Meek, 1871), Cremnoceramus crassus crassus REMARKS: Woods (1912) regarded Volvicera- ( Petrascheck, 1903), and Cremnoceramus mus as a successor of the Inoceramus lamarcki crassus inconstans ( Woods, 1912) . This is the Parkinson group. However, as rightly pointed out same assemblage as known from the southern by Tsagarély (1942), both the valve outline (parpart of the Western Interior Basin (see Walaszc- ticularly the RV) and the ornament of Volvicerazyk and Cobban, 2000), and outside, in other mus are close to Cremnoceramus ( Inoceramus areas of the Euramerican biogeographic region inconstans in Tsagarély, 1942). The single RV of (e.g., Walaszczyk, 1992; Walaszczyk and Wood, various species, as well as the juveniles LV of V. 1998). The form that dominates the assemblage cardinalensis , sp. nov., or V. exogyroides can very is C. deformis deformis (fig. 9A, D); less com- easily be mistaken for Cremnoceramus . Both mon is C. crassus crassus (fig. 9B). What is very Volviceramus and Cremnoceramus also show interesting is the parallel occurrence of C. similar morphological variability in juvenile crassus crassus and typical forms of C. crassus obliquity of growth. In the case of Volviceramus inconstans (fig. 10). This may suggest that the this is well seen in LVs; this feature is difficult to change from C. crassus inconstans to C. crassus evaluate in case of RVs.

crassus was cladogenetic in character and both Through its distinct inequivalvness, the genus forms co-occurred subsequently. Consequently, is very easily separated from other inoceramids. both should be simply referred to as C. crassus Some inequivalve representatives of the genus and C. inconstans . Inoceramus , as, e.g., Inoceramus inaequivalvis OCCURRENCE : The genus is well represented Schlüter, 1877, differ from Volviceramus in being in all localities studied herein spanning the lower distinctly less inequivalve (and they are never Coniacian: Cutpick Creek, West Thistle Creek, coiled) and in possessing more or less similar Bighorn Dam, Chungo Creek, Ram River, Sheep ornament on both valves.

River, Wapiabi Creek, Blackstone River, and Volviceramids appear abuptly above CS4, Highwood River (fig. 1). The genus is known which caps a prominent, sandier-upward heterofrom the Euramerican biogeographic region lithic succession of the lower Coniacian. Already (western Central Asia, Europe, and the Atlantic within the lowest middle Coniacian allomembers and gulf coasts of North America; North Ameri- (CA5-6) the variability of the genus is remark- FIG. 7 . Inoceramus undabundus Meek and Hayden, 1862 . A, TMP 2016.041.0426, Wapiabi Formation, Bighorn Dam, 73.0 m, lateral view of RV. B, C, TMP 2016.041.0402, Wapiabi Formation, Bighorn Dam, 41.0 m: B, lateral view, C, anterior view. D, TMP 2016.041.0427, Wapiabi Formation, Bighorn Dam, 73.0 m, anterodorsal view of LV. All photographs are ×1.

able. There appear: Volviceramus koeneni (Müller) , V. exogyroides (Meek and Hayden) , and V. cardinalensis , sp. nov. In addition to a single specimen, which shows a transitional character between V. exogyroides and V. involutus , the latter species was not noticed in this lowest interval; the first typical representatives of V. involutus are from allomember CA8.

The intraspecific variability within Volviceramus is caused mainly by the variability in the juvenile obliquity in their LVs. This allows the distinction of two morphogroups within the clade. The first group comprises low-obliquity forms (with high juvenile δ angle), characterized by a coiled or uncoiled, slender general outline. The group is represented by: V. koeneni , V. involutus , and V. stotti , sp. nov. The second group comprises forms growing obliquely in the juvenile stage (low juvenile δ angle), changing the direction of growth, to a less oblique one, later in ontogeny. This leads to a similar final architecture of the valve as the one observed in strongly inflated cremnoceramids. The oblique juvenile growth causes marked increase in valve length, and combined with subsequent geniculation and change to distinctly lower obliquity, gives a broad morphotype with massive appearance. The group is represented by V. exogyroides and V. cardinalensis , sp. nov. (see figs. 13–17). Whereas, however, the LVs in this second group resemble strongly geniculated valves in Cremnoceramus , their RVs are distinctly smaller, nongeniculated, with the typical Volviceramus RV geometry.

OCCURRENCE: The documented range of Volviceramus is middle to upper Coniacian. The genus is known from the Euramerican biogeographic region (western Central Asia, Europe, Gulf of Mexico area, American Western Interior).

Figures

FIG. 10. Cremnoceramus crassus inconstans (Woods, 1912), TMP 2016.041.0101, LV, Wapiabi Formation, Wapiabi Creek, 7.9 m, A, anterior view, B, oblique, posterodorsal view, C, lateral view of the juvenile stage. All photographs are ×1.

FIG. 7. Scaphites (S.) preventricosus Cobban, 1952, macroconch, TMP2016.041.0038, 115 m, Wapiabi Formation, Mill Creek, Alberta. A. Right lateral; B. apertural; C. ventral; D. left lateral.