Paskentana humerosa ( Stanton, 1895 )

Kaim, Andrzej, Jenkins, Robert G., Tanabe, Kazushige & Kiel, Steffen, 2014, Mollusks from late Mesozoic seep deposits, chiefly in California, Zootaxa 3861 (5), pp. 401-440 : 419

Paskentana humerosa ( Stanton, 1895)

( Fig. 8A–C , E, J)

1895 Turbo ? humerosus n. sp.; Stanton 1895: 67, pl. 12: 10, 11.

2008 Paskentana paskentaensis Stanton, 1895 ; Kiel et al. 2008b: fig. 11. 2010 Paskentana paskentaensis Stanton, 1895 ; Kiel 2010: fig. 8.5b, c.

Description. Shell turbiniform, moderately high −spired, four to five teleoconch whorls; suture distinct, incised; whorls strongly convex and evenly rounded apart from smooth subsutural ramp that ends with distinct angulation at whorl periphery. The number of spiral cords on periphery varies between five and ten, and there are approximately seven spiral cords present on the base. The juvenile whorls are additionally ornamented by sturdy axial ribs well knobbed at the intersections with spirals. The axial ribs start right on the first spiral rib delimiting the ramp and lateral flank. The axial ribs weaken on the third whorl and fade out completely on adult specimens although this process seems to be heterochronous and variable forms are present.

Material and occurrence: Many specimens (four illustrated: GZG.INV.84987-90) from Bear Creek (Valanginian, Early Cretaceous).

Remarks. Kiel et al. (2008b) considered several of Stanton's (1895) “ Turbo ” species as morphotypes of the highly variable species Paskentana paskentaensis . Accordingly, P. wilburensis ( Stanton, 1895) , P. trilineata ( Stanton, 1895) P. colusaensis ( Stanton 1895) , and P. humerosa ( Stanton, 1895) were synonymized with P. paskentaensis . The major problem with the identification of these species is the poor preservation of Stanton’s (1895) types (see the photos in Kiel et al. 2008b). Careful examination of abundant newly collected material, however, indicates that at least P. humerosa may not be synonymous with P. paskentaensis . The two syntypes of Stanton (1895) are from the Hauterivian Wilbur Springs site (locality # 5 in Kiel et al. 2008b) and in spite of their poor preservation both display a subsutural ramp and a corresponding angulation of the whorl profile. These characters are highly diagnostic for this species as was also noted by Stanton (1895: 67). The best preserved specimens of P. hu m e ro s a are from the Valanginian Bear Creek seep deposit: the material presented by Kiel et al. (2008b) included juveniles and a possible protoconch, and the newly collected specimens concerned here clearly show that the morphological variation in Paskentana species from the Bear Creek site is not as extensive as had been expected by Kiel et al. (2008b). All P. h um ero s a specimens examined possess the highly diagnostic smooth subsutural ramp. The types of P. paskentaensis clearly lack this character and therefore we decided to reinstitute P. humerosa as a valid species.

Figures

FIGURE 8. A – C, E, J. Paskentana humerosa (Stanton, 1895) from Valanginian (Early Cretaceous) seep carbonates at Bear Creek, Colusa County, California, USA. A. GZG. INV. 84987. B. GZG. INV. 84988. C. GZG. INV. 84989. E, J. Juvenile GZG. INV. 84990. D, I. Atresius liratus Gabb, 1869 from? Valanginian (Early Cretaceous) seep carbonates at Rocky Creek, Lake County, California, USA; juvenile GZG. INV. 84993. F – G. Paskentana hamiltonensis sp. nov. from from Valanginian (Early Cretaceous) seep carbonates at Bear Creek, Colusa County, California, USA. F. Paratype (GZG. INV. 84992). G. Holotype (GZG. INV. 84991). H. Paskentana globosa Kiel et al., 2008 from Tithonian (Late Jurassic) seep carbonates at Paskenta, Tehama County, California, USA; GZG. INV. 84986.