Nevadapecten Waller in Waller & Stanley, 2005
WALLER, T. R. & G. D. STANLEY JR. 2005. Middle Triassic Pteriomorphian Bivalvia (Mollusca) from the New Pass Range, west-central Nevada: Systematics, biostratigraphy, paleoecology, and paleobiogeography. Journal of Paleontology, [Memoir Paleontological Society 61], 79 (1): 1-59, figs. 1-14. [p. 46]
«Genus NEVADAPECTEN new genus
Type species.— Nevadapecten lynnae n. sp., Middle Triassic (Ladinian) of the New Pass Range, Nevada, by monotypy.
Diagnosis.— Biconvex Tosapectininae with broad umbonal angle and nearly equilateral form; byssal notch persistent; left auricles and right posterior auricle with concave free margins meeting hinge at acute angle but with overall trend of curvature forming an obtuse angle with hinge line; disk flanks very low but steep and with ornament not preserved; ornament of disk consisting of low, rounded, simple plicae of only one order on both valves; dorsal margins of right auricles straight to slightly scrolled, those of left auricles straight and not scrolled, auricular ornament not preserved except for the right posterior, which has wavy commarginal growth lines but lacks radial costae. Differentiated anterior and posterior disk sectors present only on left valve, where the posterior sector is well developed and the anterior sector only weakly developed.
Etymology.— The name combines the name of the state, Nevada, with that of the scallop, Pecten. No close phylogenetic relationship with true Pecten is implied.
Occurrence.— Known only from the coral beds of Unit E, South Canyon, New Pass Range, Nevada, late Ladinian.
Discussion.— The new genus resembles other tosapectinines in reaching a size that is large for Triassic pectinids (height 60 mm) and in having radial plicae that lack internal carinae. It differs from Janopecten and Tosapecten (Tosapecten) in having nearly equally convex valves, with a simpler pattern of low, rounded plicae. It differs from Tosapecten (Indigiropecten) in lacking a flattened early stage in the development of its left valve, in having longer auricles relative to length of disk, in lacking deeply scrolled dorsal auricular margins, and in having a persistent byssal notch. Although the auricles and growth lines on the auricles are poorly preserved, another significant difference is that these auricles appear to be obtusely triangular in Nevadapecten whereas they are acutely triangular in other tosapectinine genera. Like other Tosapectininae, Nevadapecten has anterior and posterior sectors on the left valve that are differentiated from the central sector by a change in transverse curvature and a decrease in the amplitude and/or width of radial ribs. Arkhipov and Truschchelev (1980, p. 11) and Trushchelev (1984) referred to these sectors as ‘‘lateral swellings separated from the shell by depressions’’ [my translation] and commented on differences in development of these sectors among tosapectinine genera. Those of Nevadapecten most closely resemble those of Janopecten in that the most clearly differentiated sector is the left posterior.
With regard to the morphological succession of tosapectinine genus-group taxa described above, Nevadapecten is between Janopecten and Tosapecten s.s. in terms of relative valve convexity, scrolling of auricles, and possibly depth of byssal notch. Nevadapecten also occupies an intermediate stratigraphic position, its probable late Ladinian age being between the earliest Janopecten of the Anisian and the earliest known Tosapecten s.s. of the Carnian.» THOMAS RICHARD WALLER & GEORGE D. STANLEY JR,, 2005
|
Nevadapecten lynnae n. gen. and sp.; T. R. Waller & G. D. Stanley Jr., 2005, Middle Triassic Pteriomorphian Bivalvia (Mollusca) from the New Pass Range, west-central Nevada: Systematics, biostratigraphy, paleoecology, and paleobiogeography, figure 13.
|
S. Ros-Franch, A. Márquez-Aliaga & S. E. Damborenea, 2014, Comprehensive database on Induan (Lower Triassic) to Sinemurian (Lower Jurassic) marine bivalve genera and their paleobiogeographic record, figure 36.
|
Genus NEVADAPECTEN
Waller in Waller & Stanley, 2005, p. 46 Type species.-- Nevadapecten lynnae Waller in Waller & Stanley, 2005, p. 46.
Remarks.— Waller (in Waller & Stanley, 2005) included Nevadapecten in the subfamily Tosapectininae and related it with Tosapecten and Janopecten, considering it to be intermediate between these two genera in several aspects.
Stratigraphic range.— Middle Triassic (upper Ladinian) (Waller in Waller & Stanley, 2005). According to Waller (in Waller & Stanley, 2005), Nevadapecten was reported from the upper Ladinian of New Pass Range in Nevada.
Paleogeographic distribution.— Circumpacific (Fig. 36). Circumpacific domain: Middle Triassic: Ladinian of Nevada (United States) (Waller in Waller & Stanley, 2005).
Paleoautoecology.— B, E, S, Epi, Sed; By. Nevadapecten had some features related to a swimming mode of life, such as circular shape, an almost equilateral shell, and a wide umbonal angle, but it had unequal auricles and a byssal gape, which indicates it was an epibyssate
bivalve. Mineralogy.— Bimineralic (Waller in Waller & Stanley, 2005). Outer shell layer: calcite (antimarginal fibrous). Inner shell layer: aragonite.
ROS-FRANCH, S., A. MÁRQUEZ-ALIAGA & S. E. DAMBORENEA. 2014. Comprehensive database on Induan (Lower Triassic) to Sinemurian (Lower Jurassic) marine bivalve genera and their paleobiogeographic record. Paleontological Contributions, 8: 3-219, figs. 1-61. [p. 104]
|