Indopecten Douglas, 1929
DOUGLAS, J. A. 1929. A marine Triassic fauna from eastern Persia. The Quarterly Journal of the Geological Society of London, 85: 624-648, pls. 42-46. [p. 632]
«Genus PECTEN Müller.
Subgenus INDOPECTEN nov.
Type, PECTEN CLIGNETTI Krumbeck, Palaeontographica, 1913, Suppl. iv, pt. 2, pl. ii, figs. 1 a & 1 b, p. 36.
Subgeneric characters.— Shell of medium to large size, subcircular, equilateral, inequivalve.
Right valve moderately convex, with usually five evenly-rounded main radial ribs, some or all of which bear two or more secondary ribs, which are either smooth, or, more commonly, ornamented with rows of knots or tubercles arranged at regular intervals. The furrows between the main ribs are evenly concave or flattened, and are either smooth, or, more rarely, furnished with secondary ribbing. The ribs and furrows are alike crossed by innumerable fine concentric growth-striae. Ears, moderately large and subequal, the posterior ear being provided with a shallow byssal notch. Left valve plano-convex to flat, with six angular to sub-rounded main ribs, narrower than those on the right valve, and either smooth, or bearing rarely more than one row of tubercles. Furrows broad, flattened, and frequently exhibiting pronounced secondary ribbing. Ears broad, subequal. The interior shell-structure of the left valve exhibits a peculiar series of zigzag lines, arranged in a very regular pattern, clearly visible as incised grooves in a worn shell, or as dark lines when seen through the thin outer shell-layer (see Pl. XLIV, fig. 13). The inner surfaces of both valves are strongly corrugated, so that the external ribbing is duplicated on the cast. Remarks.— With the amount of well-preserved material available in the present collection I have been able to make a critical review of this interesting group of Triassic Pectens.
I was at once met with the difficulty of referring any of the species represented to one of the many subgenera of Pectinidae; perhaps least of all to that of Aequipecten Fischer, to which most previous authors have assigned them, presumably on a superficial resemblance in the ribbing of the right valve without reference to the form of the shell, which in extreme cases approaches thai, of Vola alata ¹ L. von Buch, a piano-convex form from the Lias of Peru and Chile. It is interesting to recall that E. Jaworski suggested the derivation of the different forms of Pecten from this early plano-convex shell; for here, within the limits of variation in a single species, we can trace the gradation from a flat left valve to one of moderate convexity, in the latter instance the shell being subequivalve. This frequent pronounced inequality of the valves and the marked difference in the nature of their ribbing and ornament, together with the unique zigzag shell-structure, which is always confined to the left valve, and must not be confused with the zigzag ornament occasionally observed in later forms (for instance, Pecten fulminifer Holzapfel ²), in my opinion justifies the creation of a new subgenus for this distinctive group of Triassic Pectens. As the species constituting this subgenus attain their maximum development in the East Indies, and have rarely been recorded outside that province, I propose the name Indopecten, and have selected as the genotype Pecten clignetti Krumbeck. ³ The following species, in addition to the type, must be included in the subgenus:-- Pecten misolensis Wanner (Jaworski, 1915, pl. xliii, figs. 22-23 & p. 96).
Pecten krumbecki Jaworski (ibid. pl. xliv, fig. 2 & p. 100). Pecten subserraticosta Krumbeck ('Pal. Timor' vol. xiii, 1924, pt. 22, pl. cxciii, figs. 6-8 & p. 342). Pecten seinaamensis Krumbeck (ibid. pl. cxciii, figs. 10-12 & p. 344). ⁴ Pecten verbeeki Boettger (see Krumbeck, Palaeontographica, 1914, Suppl. iv, pl. xv, figs. 1-6 & p. 235). ⁴ Pecten microglyptus Boettger (ibid. pl. xv, figs. 7-14 & p. 237). (Lima ?) serraticosta Bittner (1899, pl. viii, fig. 12 & p. 50). Pecten clignetti var. gIabra Krumbeck (Palaeontographica, 1913, Suppl. iv, pl. ii, figs. 9-10 & p. 43).» ¹ See C. E. Baylo & It. Coquand, 'Memoire sur los Fossiles Secondaires recueillis darts le Chili par M. Ignace Domeyko' [Cretaceous & Jurassic] Mém. See. Géol. France, ser. 2, vol. iv (1851) pp. 1-47.
² E. H. Holzapfel, 'Die Mollusken der Aachener Kreide' Palaeontographica, vol. xxxv (1889) pl. xxvi, fig. 14 & p. 230. ³ The original citation of P. clignetti by Boehm was unaccompanied by either figure or description. ⁴ These two forms were first described in error as Eocene species; see O. Boettger, 'Die Terti~fformation von Sumatra' Pañaeontographica, 1880, Suppl iii, pp. 49 & 50. JAMES ARCHIBALD DOUGLAS, 1929
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Pecten (Aequipecten) Clignetti G. Boehm emend. Krumb.; L. Krumbeck, 1913, Obere Trias von Buru und Misol, plate 2, figures 1-8.
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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.
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«Genus INDOPECTEN Douglas, 1929, p. 632
Type species.-- Pecten clignetti Krumbeck, 1913, p. 36.
Stratigraphic range.— Upper Triassic (Norian–Rhaetian) (Hautmann, 2001b). Cox and others (1969) assigned it an upper Norian range. New records expanded the range of this genus (see paleogeographic distribution).
Paleogeographic distribution.— Tethys (Fig. 36).
Tethys domain: Late Triassic: Norian of western Carpathians (Ruban, 2006a), China (Wen & others, 1976; J. Chen & Yang, 1983), Oman (R. Hudson & Jefferies, 1961), Armenia (Hautmann, 2001b), Timor (Indonesia) (Krumbeck, 1924), Himalayas (Kutassy, 1931), Thailand (Vu Khuc & Huyen, 1998); Norian–Rhaetian of Iran (Hautmann, 2001b); Rhaetian of Tibet (China) (Hautmann & others, 2005), Pamira (Afghanistan) (Polubotko, Payevskaya, & Repin, 2001). Paleoautoecology.— B, E, S, Epi-Un, FaM; By-R-Sw. Some of Indopecten species, like I. glaber Douglas, 1929, could swim, as suggested by their ligament type (so-called alivincular-alate according to Hautmann, 2004), which would be fit enough for the constant opening and closing of the valves required by a swimming activity (Hautmann, 2004). The external morphology is also compatible with a swimming habit, according to S. M. Stanley (1972). It probably lived mostly reclined, but it could swim occasionally. However, other species have a byssal notch, and their shell morphology is not suitable for swimming, so these were probably epibyssate (see Hautmann, 2001b).
Mineralogy.— Aragonitic (Hautmann, 2006a). According to Waller (2006), the Indopecten inner shell layers are usually recrystallized, so they were probably aragonitic. Although the microstructure of the outer shell layer is unknown, its mineralogy was calcitic. However, Hautmann (2006a) studied the microstructure of two species of Indopecten [I. serraticostata (Bittner, 1899) and I. glaber (Douglas, 1929)] and he concluded that all the shell was composed of a single microstructure (probably cross-lamellar) and was entirely aragonitic.»
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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«Another remaining problem related to clade 9 involves the genus Indopecten Douglas, 1929. Members of this genus are exclusively Upper Triassic (Norian–Rhaetian) and occur mainly in the eastern Tethyan realm (Hayami, 1989: 6). Like many tosapectinids, they are generally of large size and commonly have a right valve that is substantially convex and a left valve that is less convex, flat, or even concave. In some species, the auricles may be acutely trigonal, not unlike tosapectinid auricles, although the auricles of other Indopecten species, e.g. I. seinaamensis (Krumbeck, 1924), may be more rounded and may have only a shallow byssal notch, thus resembling auricular configurations that are common in the Entolioididae. As in the Neitheidae, the coarse radial plicae of Indopecten have carinate internal edges. Unlike any known tosapectinids or neitheids, however, Indopecten possesses internal divaricating riblets on the left valve that are indistinguishable from a filosus structure, suggesting that this may be a plesiomorphic character that is carried forward from the Entolioididae. Unlike members of the Entolioididae, however, Indopecten does not have an extensive outer layer of columnar prismatic calcite on its right valve. Neither the detailed structure of the nonprismatic calcitic outer layers nor the structure and mineralogy of the inner shell layers are known, although the tendency for the inner layer to be coarsely recrystallized relative to the outer layers suggests that it was originally aragonitic. The hinge dentition of Indopecten is dominated by resilial teeth, as in the Entolioididae and also in clade 9. At this time, therefore, the systematic position of Indopecten is uncertain.»
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. [p. 330, 331]
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