Paskentana paskentaensis ( Stanton, 1895 )

Kiel, Steffen, Campbell, Kathleen A., Elder, William P. & Little, Crispin T. S., 2008, Jurassic and Cretaceous gastropods from hydrocarbon seeps in forearc basin and accretionary prism settings, California, Acta Palaeontologica Polonica 53 (4), pp. 679-703 : 688-689

Paskentana paskentaensis ( Stanton, 1895)

Fig. 6 .

1895 Turbo paskentaensis sp. nov.; Stanton 1895: 64–65, pl. 12: 5–6. 1895 Turbo wilburensis sp. nov.; Stanton 1895: 65, pl. 12: 15.

1895 Turbo trilineatus sp. nov.; Stanton 1895: 65–66, pl. 12: 12. 1895 Turbo colusaensis sp. nov.; Stanton 1895: 66, pl. 12: 14.

1895 Turbo ? humerosus sp. nov.; Stanton 1895: 67, pl. 12: 10, 11. 2006 Thin−shelled possible provannid; Campbell 2006: 382, fig. 6A.

Material.— Stanton’s (1895) type material [ USNM 23067 (= T. paskentaensis ), USNM 23068 (= T. wilburgensis ), USNM 23069 (= T. trilineatus ), USNM 23070 (= T. colusaensis ), USNM 23072 and 23073 (= T.? humerosus)], and 163 specimens from subsequent collections. Stanton’s (1895) specimen of Turbo paskentaensis from Paskenta (site 2) illustrated here on Fig 6I is designated as lectotype.

Description.—Shell ovate fusiform, moderately high−spired, apical angle 58–60°, four to five teleoconch whorls, with globose last whorl; suture distinct, incised; whorls strongly convex, and vary from evenly rounded to angulate, resulting from straight subsutural ramp that ends with distinct angulation at whorl’s periphery; if present, up to two spiral cords on the ramp; number of spiral cords on periphery varies between five and ten, up to ten spiral cords present on the base; spiral cords either of equal strength, or show alternating pattern of strong and weak ones, or strength decreases towards base; interspaces either of same width as spirals or slightly wider, in rare cases up to three times as wide; growth lines vary in strength and cause fine crenulations, nodes, or strong, half−tube−like spines or scales when they cross spiral cords; this pattern is usually strongest on periphery below ramp, where it can form a spiny or tuberculate shoulder, and tends to become slightly weaker towards the base; aperture subovate to lenticular, columella convex and smooth.

Discussion.—This species shows great morphologic plasticity, ranging from individuals having well−rounded whorls with beaded spiral ornament, to individuals having strongly shouldered whorls and ornament where the intersections of axial growth lines with spiral cords form small scaly spines. Similar scaly ornament can also be seen on specimens with well−rounded whorls, whereas other individuals have a strong shoulder but almost smooth spiral cords. This plasticity may have led Stanton (1895) to erect five different species, although he noted that they are rather closely related. We have examined Stanton’s material, as well as other museum collections and new field collections, and have found a continuum in these characters. Therefore we synonymize Turbo wilburensis , Turbo trilineatus , and Turbo colusaensis with Paskentana paskentaensis as this was the first among the species that Stanton (1895) described.

Also a synonym of Paskentana paskentaensis is Turbo ? humerosus Stanton, 1895. Stanton’s material includes three specimens, of which he illustrated two, and he provided two USNM numbers (23072 and 23073). However, he did not specify which specimen had which number, and all specimens are in the same box along with a label stating both numbers. Two of his specimens are steinkerns, only one has a moderate amount of shell material preserved. This latter specimen (Stanton’s fig. 11, our Fig. 5M ) is here designated as the lectotype of Turbo ? humerosus Stanton, 1895, and given the USNM number 23072. Our new material shows that T.? humerosus falls within the broad morphologic range of Paskentana paskentaensis , and therefore T.? humerosus is synonymized with Paskentana paskentaensis .

Superficially similar to Paskentana paskentaensis is the “epitoniid gastropod from Memi” from a vent community in the Turonian (Late Cretaceous) Troodos ophiolite on Cyprus ( Little et al. 1999: fig. 2I) because it has a similar scaly sculpture as some specimens of Paskentana paskentaensis (e.g., Fig. 6A, F ). But the Troodos species is higher spired and has fine spiral microornament that we have not seen on any of our Paskentana species.

Stratigraphic and geographic range.—Tithonian (Upper Jurassic) to Lower Cretaceous, restricted to seep carbonates in the Great Valley Group and Franciscan Accretionary Complex, California, USA. This species is widespread and occurs at the following localities: Paskenta, site 2, and NW Berryessa, site 10 (Tithonian), Little Indian Valley , site 6, and Bear Creek, site 4 (Valanginian?), Foley Canyon, site 8 (Valanginian–Hauterivian), Wilbur Springs, site 5 (Hauterivian), Rice Valley, site 3 (Lower Cretaceous), Gravelly Flat, site 15, and E and W Berryessa, sites 12 and 11 (possibly Lower Cretaceous).

Figures

Fig. 6. Abyssochrysoid gastropod Paskentana paskentaensis (Stanton, 1895) from Late Jurassic and Early Cretaceous seep carbonates in California, USA. A. Small specimen (CAS 70392) with strong scaly sculpture from Bear Creek (Valanginian; site 4); apertural (A1) and lateral (A2) views. B. Specimen (CAS 70393) with broad shoulder from Bear Creek (Valanginian; site 4). C. Specimen (UCMP 555097) with broad shoulder and almost smooth spiral sculpture, from Little Indian Valley (Valanginian?; site 6). D. Juvenile specimen (UCMP 555104) from Bear Creek (Valanginian; site 4), close−up on first whorls (D1) and entire specimen (D2). E. Isolated partial larval shell (UCMP 555105) from Bear Creek (Valaginian; site 4) that most likely belongs to Paskentana paskentaensis. F. Specimen (UCMP 154113) without shoulder and fine scaly sculpture, from Rice Valley (Hauterivian?; site 3). G. Specimen (UCMP 13701) without shoulder, from Wilbur Springs (Hauterivian; site 5). H. “Turbo” wilburensis Stanton, 1895 (pl. 12: 15), lectotype (USNM 23068) from Wilbur Springs (Hauterivian; site 5). I. “Turbo” paskentaensis Stanton, 1895 (pl. 12: 6), lectotype (USNM 23067) from Paskenta (Tithonian; site 2). J, K. “Turbo?” humerosus Stanton, 1895 from Wilbur Springs (Hauterivian; site 5). J. Lectotype (USNM 23072). K. Paralectotype (specimen illustrated by Stanton 1895: pl. 12: 10).

Fig. 5. Late Jurassic and Early Cretaceous abyssochrysoids Hokkaidoconcha spp. and Abyssochrysos? giganteum sp. nov. from seep carbonates in California, USA. A–C. Hokkaidoconcha occidentalis (Stanton, 1895). A. Lectotype (USNM 23077) from Paskenta (Tithonian; site 2). B. Specimen (CAS 70391) with well−developed spiral sculpture from Wilbur Springs (Hauterivian; site 5). C. Specimen (UCMP 555091) with poorly developed spiral sculpture from NW Berryessa (Tithonian; site 10). D, E. Hokkaidoconcha tehamaensis sp. nov. from Paskenta (Tithonian; site 10). D. Holotype (UCMP 555092); apertural (D1) and lateral (D2) views. E. Paratype (CAS 70390), note fading axial ribs on flank.F, G. Hokkaidoconcha morenoensis sp. nov. from Moreno Gulch (Santonian; site 14) F. Holotype (LACMIP 13483) with well−developed axial ribs and spiral sculpture on base. G. Paratype (LACMIP 13484) with fading axial ribs on later whorls. H. Hokkaidoconcha bilirata sp. nov., holotype (UCMP 555093) from Wilbur Springs (Hauterivian; site 5). I. Hokkaidoconcha sp. (UCMP 555094) from NW Berryessa (Tithonian; site 10). J, K. Abyssochrysos? giganteum sp. nov. from E Berryessa (Lower Cretaceous; site 12). J. Holotype (UCMP 555095). K. Paratype (UCMP 555096).