Athlopecten athleta (Zittel, 1865)
ZITTEL, K. A. 1865. Fossile Mollusken und Echinodermen aus Neu-Seeland. In F. von Hochstetter, M. Hörnes & F.R. von Hauer (Eds.), Paläontologie von Neu-Seeland. Reise der Österreichischen Fregatte Novara, Geologischer Theil, 1 (2): 15-68, pls. 6-15. [p. 49, pl. 10, fig. 1]
1864 Pecten athleta Zittel, 1865
1913 Pecten (Patinopecten) marshalli Suter, 1913
1913 Pecten (Patinopecten) marshalli Suter, 1913
K. A. Zittel, 1865, plate 10.
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«Char. Testa maxima, suhrotundata, aequilatera, inaequivalvis, utraque valva costis 10 principalibus et costis inierstitialibus ornata. Valva sinistra paullo convexa, costis rotundatis, inornatis, valva dextra convexa, umbonibus paullo inflatis. Auriculae magnae, aequales.
Höhe 175 Millim., Länge 185 Millim. Die mächtig grosse Schale ist gerundet, etwas länger als hoch, gleichseitig, ungleichklappig. Beide Klappen tragen auf ihrer Oberfläche etwa 10 Hauptrippen, die von den Buckeln bis an den Stirnrand herablaufen; zwischen diesen schieben sich in den breiten Zwischenfeldern entweder zwei oder eine Rippe ein, die nur ungefähr zwei Drittel der Schalenhöhe erreichen. Die Rippen sind abgerundet, ohne Verzierung. Die linke Schale sehr wenig gewölbt, die Zwischenrippen gehen auf dieser Klappe weiter herauf, als auf der gewölbten rechten Klappe, deren Wii-bel nicht über den Schlossrand hervorragt. Die grossen Ohren sind auf beiden Seiten von gleicher Grösse. Unter den jetzt im stillen Ocean lebenden Arten ist keine, die dem P. Athleta nahe käme. Dagegen erinnert er in seinem Habitus und Grösse an einige in Miocänscliichten Europa's vorkommende Arten. Vorkommen: Motupipi in der Massaere-Bay, Südinsel.» KARL ALFRED VON ZITTEL, 1865
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«Type material. Pecten athleta holotype NHMW 1959/335/37, from locality 10, Takaka Limestone (Waitakian, late Oligoceneearly Miocene), Tarakohe; plaster replica GNS TM4211. Pecten marshalli holotype not seen, apparently in Otago Museum (?). Suter (1913b, p. 296) stated that the holotype was ‘in the collection of Dr. P. Marshall, Otago University, Dunedin’, but it was not acquired by the New Zealand Geological Survey (now GNS Science) with the purchase of Marshall’s collection in 1947; not in Otago University Geology Department; from ‘Muddy terrace, Waikaia’, northwest of Gore, Southland, Duntroonian (late Oligocene).
Dimensions. Holotype of Pecten athleta: H 168, L 190 mm; illustrated immature specimen, GS9805, F44/f9501, Chatton Formation (Duntroonian, late Oligocene), Wendon Valley, Southland: H 63.3, L 64.1 mm; small illustrated adult, GS9806, F44/f9668, Chatton Formation (Duntroonian), Shell Gully, Chatton, Southland: right valve H 119.1, L 124.6 mm, left valve H 118.5, L 116.8 mm; moderately large specimen illustrated by Beu & Maxwell (1990, pl. 11b), GS990, R14/f6012, coastal section between Gibson’s and Carter’s Beaches, west coast south of Waikato Heads, Southwest Auckland, Waitakian: H 153.7, L 166.1 mm.
Remarks. Athlopecten athleta is well known as the largest pectinid occurring in New Zealand, reaching c. 200 mm in length. Biostratigraphically it is very useful because of its limitation to Waitakian and Duntroonian rocks (late Oligoceneearliest Miocene). The coarse but very irregular, widely spaced radial costae of evenly convex cross-section, the regular, thin, widely spaced, commarginal lamellae, and the gone but obvious shagreen microsculpture on at least the early part of the disc, particularly on immature specimens, render this species highly distinctive. The right valve is a little more inflated and a little longer (antero-posteriorly) than the left valve, so the left valve fits slightly inside the right at the anterior and posterior ends when the valves are articulated. The auricles are separated from the disc by deep grooves on both valves. Immature specimens have a very deep byssal notch in the right valve (Fig. 11C) and a functional ctenolium with 6-7 robust teeth, but the notch is reduced and the ctenolium not functional in adults. The illustrated juvenile right valve (Fig. 11C; GS 9805, F44/f9501, Wendon Valley, Southland; Chatton Formation, Duntroonian) seems originally to have had fine shagreen microsculpture over most or all of the exterior, but it evidently is easily removed, and adheres now only to the central and posterior areas of the disc between radial costae. Juvenile sculpture commences as c. 25 narrow, sharp-crested, widely spaced radial costellae, tending to be arranged in pairs with wider interspaces. The costellae widen down the shell to form pairs of wider, more prominent costae by a height of c. 40 mm. Some initially narrow costellae form narrow secondary costae in primary radial interspaces lower down the disc, whereas others form the primary costae. Similar narrow, sharp-crested costae are present on the juvenile left valve, but there only 11 costae. On more adult specimens, the left valve bears only about 10-11 relatively wide, prominent, widely spaced radial costae, whereas the right valve bears twice as many lower, narrower, more closely spaced costae and many secondary and more minor, highly irregular riblets. Commarginal sculpture on the right valve remains prominent on most reasonably well preserved specimens, and consists of many relatively closely spaced, steeply outward-inclined scales, tending to be triangular on the costae, more-or-less linked between costae to form commarginal ridges on some specimens. In contrast, commarginal sculpture is rarely preserved on the left valve; on unusually well preserved specimens it consists of very thin, low, irregular, widely spaced, subvertical to outwardly inclined scales on the costal crests, linked weakly across the radial interspaces in some places, but about twice as far apart as those on the left valve (Figs 11D, 12B). Commarginal ridges are more prominent and more closely spaced on the auricles than on the disc. There is no sign of internal rib carinae on the almost completely smooth, non-plicate interior, and the hinge consists only of small dorsal teeth and sockets.
The holotype of Athlopecten athleta is much less complete than Zittel’s (1865, pl. 10, fig. 1) illustration indicates, and has been abraded severely, completely through the shell in one area. More of the shell is missing from the lower posterior margin than the drawing indicates, and much less of the surface is radially costate than in the drawing; 10 poorly defined, heavily abraded radial costae are present, indicating that it is a left valve. Suter (1913b, pl. 13, figs 1, 2) illustrated both the holotype of Pecten marshalli, an unusually strongly costate left valve with weak secondary sculpture, and a typical, large specimen of A. athleta, also identified as Pecten marshalli, probably merely indicating that Suter had seen little good material of A. athleta. There is no doubt that these two forms intergrade. Huge but poorly preserved specimens of A. athleta, similar to the holotype in preservation, are abundant in blocks of Takaka Limestone along the shore at the probable type locality, near the former Tarakohe Quarry to the east of Takaka, Northwest Nelson. Presumably the holotype is a poorly preserved specimen because Hochstetter and his companions could extract only a weathered specimen from the severely cemented Takaka Limestone. A second specimen of Athlopecten athleta in NHMW, an unregistered umbonal fragment 60 mm wide with partial auricles, is labelled ‘Pecten sp., Whaingaroahafen, W. Küste, Neu-Seeland’. It was not referred to by Zittel (1865) and is not a type specimen. As the illustrated specimen was the only one used and referred to by Zittel, it is considered to be the holotype. The relationships of Athlopecten athleta were discussed briefly by Beu & Raine (2009, p. BM131), who concluded that this type of large, shagreen-bearing scallop seems likely to be most closely related phylogenetically to tribe Fortipectinini in the North Pacific, and to genera that have radiated from there. These seem to include at least Fortipecten Yabe & Hatai, 1940, Patinopecten Dall, 1898, and Mizuhopecten Masuda, 1963 (Miocene-present) in the North Pacific, Equichlamys Iredale, 1929 (Pliocene-present) in southern Australia, and Jorgechlamys del Rio, 2004 and Reticulochlamys del Rio, 2004 (Oligocene-Miocene) in Argentina. However, Athlopecten would be the one of the earliest recorded members of this group if the suggested relationship is correct (although little earlier than the earliest records of Jorgechlamys and Reticulochlamys), and the origin of the tribe and genus is obscure.» BEU, A. G., S. NOLDEN & T. A. DARRAGH. 2012. Revision of New Zealand Cenozoic fossil Mollusca described by Zittel (1865) based on Hochstetter’s collections from the Novara Expedition. Memoirs of the Association of Australasian Palaeontologists, 43: 1-69, figs. 1-21. [p. 27, 29]
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Athlopecten athleta (Zittel, 1865); A. G. Beu, S. Nolden & T. A. Darragh, 2012, Revision of New Zealand Cenozoic fossil Mollusca described by Zittel (1865) based on Hochstetter’s collections from the Novara Expedition, figure 11A, 11C, 11D.
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