Mollusks from late Mesozoic seep deposits, chiefly in California
Author
Kaim, Andrzej
Author
Jenkins, Robert G.
Author
Tanabe, Kazushige
Author
Kiel, Steffen
text
Zootaxa
2014
3861
5
401
440
journal article
42509
10.11646/zootaxa.3861.5.1
0b368704-d9cc-4a82-8248-bc4c06dcf781
1175-5326
252462
E62DB6C3-0C5F-4898-99C4-1BEC70DD1734
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.