Leopecten gatunensis (Toula, 1909)
TOULA, F. 1909. Eine jungtertiäre Fauna von Gatun am Panama-Kanal. Jahrbuch der Kaiserlich-Königlichen Geologischen Reichsanstalt, Wien, 58: 673-760 [p. 711, pl. 26 (2), fig. 2]
1909 Pecten (Flabellipecten) gatunensis Toula, 1909
1917 Pecten (Amusium?) correctus Pilsbry & Johnson, 1917
1917 Pecten (Amusium?) correctus Pilsbry & Johnson, 1917
F. Toula, 1909, plate 26.
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«1. Zwei größere Individuen, das eine wohl erhalten mit fast gleichohriger, leicht aufgewölbter Klappe, trägt 25 breite, oben flache Radialrippen und feine, aber scharf ausgeprägte Anwachslinien. Die ersteren sind durch etwas schmälere vertiefte Zwischenräume geschieden. Die von Köhler und Kobelt als Pecten novae Zelandiae Reeve (verbessert = laticostatus Gray [pag. 149 u. 283, Taf. XLII, Fig. 1 u. 2]) bezeichnete Art hat in der Art der Rippung große Ähnlichkeit, doch sind nur 19 Rippen vorhanden.
Pecten (Flabellipecten) flabelliformis Brocchi, wie er in seiner rechten Klappe von Fr. Sacco (1. c. Parte XXIV, Taf. XVI, Fig 1 a) abgebildet wird, hat trotz der etwas größeren Anzahl von Radialrippen (zirka 30 gegen 25 an meinem Stück) die größte Ähnlichkeit, so daß ich das Stück von Gatun dieser Art anschließen möchte. Auch Pecten Besseri Andr., wie ihn M. Hörnes (Wiener Becken, II, Taf. LXII und LXIIl, Fig. 1—5) von Neudorf abbildet, gehört zu den verwandten Arten, hat aber nur 21—23 Rippen, von welchen jederseits etwa vier nur schwach entwickelt sind. R. Arnold hat vor kurzem aus Kalifornien einen Pecten (Patlnopecten) caurinus Gould aus dem Pliocän von San Pedro zur Abbildung gebracht (Bull. Nr. 321, U. S. G. S. 1907, Taf. XVI), dessen rechte Klappe 21 Radialrippen trägt. Er gehört offenbar gleichfalls zu den näher verwandten Formen, wenn auch die Ohren etwas anders umgrenzt sind, wie ein Vergleich der Abbildungen sofort ergibt. Die Umgrenzung der Ohren unterscheidet auch Pecten Besseri Andr., bei dem sie, gegen die Schale hin ausgeschnitten erscheinen und nicht so plötzlich verjüngt. Auch sind die Furchen der Innenseite etwas anders. Die Anwachsstreifung ist bei meinem Stück gegen den Stirnrand zu besonders scharf ausgeprägt.» FRANZ TOULA, 1909
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«Remarks.— Woodring (1982) interpreted "Flabellipecten" gatunensis broadly, subdividing the species into four subspecies with a collective stratigraphic range from late Oligocene to Pliocene in the tropical American region, particularly in Panama. Th ree of these subspecies – F. g. protistus Woodring, 1982; F. gatunensis s. s., and F. g. macdonaldi (Olsson, 1922) – were regarded as parts of a single lineage in a stratigraphic succession, whereas the fourth, F. g. tapeinus Woodring, 1982, was regarded as an off shoot from the main lineage. Waller (2007) presented evidence mainly from a study of hinge dentition that three of these so-called subspecies belong in Leopecten, not Flabellipecten, and reexamined phylogenetic relationships. He placed Woodring's oldest subspecies, F. gatunensis protistus, into the genus Amussiopecten (in the combination A. protistus) on the basis of the presence of intermediate hinge teeth as well as the fading out of radial ribs toward the ventral margin. He also determined that F. g. tapeinus is a junior synonym of F. g. macdonaldi, which was raised to species rank (as L. macdonaldi).
Leopecten gatunensis, as now understood, is a species that in Panama ranges from the Lower Member of the Alhajuela Formation to the middle Gatun Formation (Woodring's stratigraphic range for his Flabellipecten gatunensis s. s.). The middle to upper Gatun Formation has recently been dated as early Late Miocene (zone NN10 and zone N16 (= M13a), equivalent to the middle Tortonian stage of Europe) on the basis of calcareous nannoplankton and planktic foraminiferans (Collins et al., 1996: 687). The Alhajuela Formation has not been precisely dated but the overlying lower Gatun Formation as been dated as zone N14 (= M11), or early Tortonian (Collins et al., 1996: 676), leading to the presumption that the Alhajuela is probably late Middle Miocene in age. Leopecten gatunensis in Panama is variable in rib amplitude (as documented by Woodring, 1982: 584) and the degree to which ribs on the disk approach the disk flanks or give way to nonribbed shoulders adjacent to the flanks. The most extreme variation occurs among the geologically oldest members of the species that occur in the lower member of the Alhajuela Formation (Woodring, 1982: pl. 110, fig. 13). Compared to more typical L. gatunensis, the right valve that Woodring illustrated as well as four additional right valves collected at the same locality (USGS 5906a) have narrower ribs, some of which develop 1 or 2 grooves on their crests in late ontogeny. Furthermore, the ribs continue right up to the disk flanks, there being no nonribbed shoulders as in more typical L. gatunensis. Close inspection with a microscope, however, revealed that the grooved rib crests are the result of repaired injuries caused by boring epifauna. The five specimens of Leopecten gatunensis collected in the Dominican Republic are from two localities, NMB 17272 and NMB 17274, both on the Río Yaque del Norte. Both of these localities are in the "Arroyo López section" of Saunders et al. (1986: text-fig. 26), with an age indicated in their table 3 as late Miocene (lower NN11) and correlating with the lower Cercado Formation in the Río Gurabo section. Using the Neogene Time Scale of Gradstein et al. (2004: fig. 21.1), lower zone NN11 is late Tortonian in age and therefore somewhat younger than the youngest L. gatunensis in Panama. In Panama, according to Woodring (1982), L. gatunensis s. s. is absent in the upper part of the Gatun Formation and is replaced in the overlying Chagres Sandstone by the taxa that he called Flabellipecten gatunensis macdonaldi and F. g. tapeinus (regarded as synonyms and combined under L. macdonaldi by Waller, 2007: 937).» WALLER, T. R. 2011. Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley. Bulletins of American Paleontology, 381: 1-197, pls. 1-18. [p. 108, 109]
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Leopecten gatunensis (Toula, 1909); T. R. Waller, 2011, Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley, plate 14, figure 14.
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