Weyla J. Böhm, 1922
BÖHM, J. 1922. Zur systematischen Stellung der Gattung Neithea Drouet. Jahrbuch der Preussischen Geologischen Landesanstalt zu Berlin, 40 (2): 129-147, text-figs. 1, 2. [p. 138]
«Da Pecten alatus BUCH weder der Gattung Pecten O. F. MÜLLER noch der Gattung Neithea DROUET angelhört, so bringe ich für die durch ihn vertretene Lias-Gruppe einstweilen den Namen Weyla in Vorchlag»
JOHANNES BÖHM, 1922
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Pecten alatus, De Buch; E. Bayle & H. Coquand, 1851, Mémoire sur les fossiles recueillis dans le Chili par M. Ignace Domeyko, plate 5, figures 1, 2.
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Weyla (Weyla) alata alata (von Buch, 1838); S. E. Damborenea, 1987, Early Jurassic Bivalvia of Argentina, Part 2, Superfamilies Pteriacea, Buchiacea and part of Pectinacea, plate 9, figure 1; plate 10, figures 1-5.
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«Type species.-- Pecten alatus Buch, 1838, p. 55.
Remarks.— Although Damborenea (1987b) and Damborenea and Manceñido (1988) regarded Weyla as a neitheid, this family was not included in the systematic arrangement proposed by Amler (1999), which is followed here. Waller (2006) included this genus in the family Pectinidae by the presence of ctenolium. Stratigraphic range.— Lower Jurassic (Hettangian–Toarcian) (Damborenea & Manceñido, 1988; Aberhan, 1994a). Cox and others (1969) assigned it a Upper Triassic–Middle Jurassic range, but they included three subgenera: W. (Weyla) from the Lower Jurassic, W. (Pseudovola) Lissajous, 1923, p. 169, from the Middle Jurassic, and W. (Tosapecten) Kobayashi & Ichikawa, 1949b, p. 166, from the Upper Triassic. Currently, Pseudovola and Tosapecten are considered to be separate genera (Hayami, 1975; Damborenea, 1987b), so the remaining range is Lower Jurassic. We include two subgenera of Weyla from the Lower Jurassic, W. (Weyla) and W. (Lywea) Damborenea, 1987b. Damborenea and Manceñido (1988) indicated that the genus was present from Sinemurian to Toarcian, and subsequently it was found in Hettangian deposits (Aberhan, 1994a; Liu, 1995; Damborenea, 1996a). Lucas and Estep (1997, p. 45, fig. 1c and 1d) mentioned and figured Weyla from Carnian beds of Sonora (Mexico), but these specimens were reassigned to Mysidioptera by Damborenea in Damborenea and Gonzalez-León (1997); Lucas and Estep (1997) also reported other specimens from the Sinemurian of the same area. Paleogeographic distribution.— Circumpacific and Austral (Fig. 36). Although the genus is also present in the Tethys domain, it is recorded there only after the beginning of the Pliensbachian (Calzada, 1982; Liu, 1995; Fraser, Bottjer, & Fischer, 2004; Valls, Comas-Rengifo, & Goy, 2004). The genus originated in the Pacific margin and then extended to the western Tethys through the Hispanic Corridor or Proto-Atlantic (Damborenea & Manceñido, 1979, 1988; Aberhan, 2001). See Damborenea and Manceñido (1979) for a complete distribution of the genus. Circumpacific domain: Early Jurassic: Hettangian–Sinemurian of western Canada (Aberhan, 1998a), Mexico and Texas (Liu, 1995), Chile (Aberhan, 1994a); Sinemurian of Sonora (Mexico) (Damborenea in Damborenea & González-León, 1997; Lucas & Estep, 1997; Scholz, Aberhan, & González-León, 2008), Chile (Escobar, 1980), Peru (Rangel, 1978). Austral domain: Early Jurassic: Sinemurian of Argentina (Damborenea & Manceñido, 2005b; Damborenea & Lanés, 2007). Paleoautoecology.— B, Se, S, Un, Sed; R. From the observation of specimens in life position and analysis of the shell morphology (Damborenea & Manceñido, 1979, 1988; Damborenea, 1987b), it was inferred that Weyla was sedentary and lived semi-infaunally as a recliner, without byssus attachment in the adult stage. Mineralogy.— Bimineralic (Carter, 1990a, p. 260, 263). Little is known about the microstructure of the shell of Weyla; the inner shell layer is aragonitic and with cross-lamellar structure. Data provided for the family Pectinidae. Outer shell layer: calcite (prismatic). Inner shell layer: aragonite (cross-lamellar).» 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. 100]
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«The derivation of Neitheidae from Tosapectinidae is problematic because of the extensive time gap between the last tosapectinid in the latest Triassic and the first neitheid in the Lower Cretaceous. Some authors have partially filled this gap by assuming that the Lower Jurassic genus Weyla Böhm, 1922, a highly right-convex pectinoidean, is ancestral to Neithea and Hertlein (1969: N371) even regarded Tosapecten as a subgenus of Weyla. Damborenea (1987: 167) argued for a close relationship between Weyla and Neithea on the basis of similarities in hinge structure and 'the apparent lack of a ctenolium’ in both genera, and she followed Sobetski (1960) in placing both in the family Neitheidae. I, however, agree with Hayami (1961: 161) and Dhondt (1973: 9), both of whom considered Weyla and Tosapecten to be distinct genera and rejected the idea of their close phylogenetic relationship. Waller (in Waller & Stanley, 2005: 45) discussed a number of morphological characters of Weyla that do not occur in either Tosapecten or Neithea, not the least of which is the presence of a ctenolium in the early ontogeny of Weyla (Fig. 10A, B), indicating that this genus belongs in the Pectinidae. As for hinge structures, Weyla (Weyla) has a unique hinge configuration unlike that of Neithea. In Weyla, a distinct hinge plate is present, and its entire surface is a zone of apposition having transverse vertical ridges that interlock between the two valves (Fig. 10C, D). The ridged areas of the right valve are concave (slightly more deeply concave adjacent to the resilifer), and those of the left valve are correspondingly convex, thus providing tightly interlocking articulation between closed valves. The transverse ridges do not extend into the outerligament grooves, which are not crenulated. In this figured specimen, which is considerably smaller than the specimen of Weyla (Weyla) alata angustecostata figured by Damborenea (1987: Fig. 23), there is no sign of the ‘rudimentary tooth’ on the anterior side of the right resilifer that she labelled in her figure, and her ‘vertically striated lamella’ on the posterior side of the resilifer is, in the smaller specimen figured herein, simply the sharp ventral edge of the hinge plate. In Neithea (Fig. 9A, B), the zones of apposition on the hinge plates are very narrow strips bordering the ventral edge of the ligament groove on each side of the resilifer. The resilial teeth of Neithea begin very early in ontogeny and, at the earliest stage thus far observed, they are not part of these crenulated apposition zones.
Weyla is probably descended from the Pseudopecten dentatus group of the Lower Jurassic, a group in the Pectinidae that shares details of the hinge structure, strongly cross-ridged disk flanks, and tonguing commarginals on the disk surface. The strong differential valve convexity attained by Weyla represents an adaptation to a reclining mode of life. This specialized condition may have restricted evolutionary pathways, resulting in the extinction of this clade near the end of Early Jurassic time.»
WALLER, T. R. 2006. Phylogeny of families in the Pectinoidea (Mollusca: Bivalvia): importance of the fossil record. Zoological Journal of the Linnean Society, 148: 313-342, figs. 1-12. [p. 329, 330]
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