Mesopeplum burnetti (Zittel, 1865)
ZITTEL, K. A. 1865. Fossile Mollusken und Echinodermen aus Neu-Seeland. Reise der Österreichischen 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. 51, pl. 10, figs. 2a, 2b]
1864 Pecten burnetti Zittel, 1865
K. A. Zittel, 1865, plate 10.
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«Char. Testa orbicularis, aequilatera, convexa, 4-7 plicata, costis numerosis radiata. Costae inaequales, inornatae, rotundatae, interstitiis subaequalibus disjunctae. Auriculae irradiatae.
Höhe 30 Millim., Länge 30 Millim. Sehale rund, eben so hoch als lang, und sehr gewölbt, gleichseitig und wahrscheinlich ungleichklappig, doch liegen nur die convexen Klappen vor. Die Oberfläche ist mit zahlreichen Längsrippen bedeckt und trägt etwa 4 — 7 Falten. Die Längsrippen sind abgerundet, ohne alle Verzierung und von verschiedener Stärke; die auf dem Rücken einer Falte befindlichen sind dicker, als die in den dazwischen liegenden Furchen. Die Ohren sind ziemlich gross, vermuthlich glatt. Name nach Herrn Burnett in Nelson. Vorkommen: Motupipi in der Massaere-Bay, Prov. Nelson.» KARL ALFRED ZITTEL, 1865
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«Type material. Pecten burnetti three syntypes NHMW 1959/335/39/1-3, from locality 10, Tarakohe, from Takaka Limestone (Waitakian, latest Oligocene-earliest Miocene); plaster replicas GNS TM4225, 4226. This species was named after James Burnett, of Nelson, former manager of the Motupipi Coal Mine, who travelled with Hochstetter in Golden Bay (Zittel 1865, p. 51). The most complete specimen in Zittel’s ¿ gures (1865, pl. 10, ¿g. 2a) (NHMW 1959/335/39/1) is here designated the lectotype of Pecten burnetti Zittel (Fig. 15B).
Dimensions. Cast of lectotype: H 31, L 36 mm; illustrated specimens, GS1466, N25/f8497, Tarakohe Mudstone (Waitakian), Tarakohe Quarry, Takaka; right valve: H 40.3, L 41.3 mm; left valve: H 30.0, L 30.6 mm; largest specimen in collection: H 39.4, L 45.0 mm; large example of Miocene prominently ribbed specimen referred to M. burnetti, GS9445, X18/f7529, 20 m south of Cook County Quarry, Pongaroa, northeastern Wairarapa, Tongaporutuan (late Miocene): H 56.5, L 59.7 mm.
Remarks. Mesopeplum burnetti is the common, widespread, early Miocene and perhaps Oligocene-early Pliocene Mesopeplum species occurring in limestone and other shallow facies throughout New Zealand. The more prominent, clearly defined radial costae present on all specimens distinguish it from the Nukumaruan-present day species M. convexum (Quoy & Gaimard, 1833), in which the radial sculpture is more variable, and weaker than that of M. burnetti in most specimens. M. burnetti is very similar to the Australian Miocene species M. incertum (Tenison Woods, 1865) (Beu & Darragh 2001, p. 158, figs 56B, E-G) and further research is required to be certain these are two distinct species, but most New Zealand Oligocene-early Miocene specimens consistently reach a significantly larger size and have more prominent radial costae (as distinct from radial folds) than Australian specimens. Specimens also are quite variable in shape and inflation, varying from a highly inflated and relatively weakly plicate form (Fig. 13E), most specimens of which are right valves, to a weakly inflated but strongly radially sculptured form (Fig. 12C), all specimens of which are left valves. Specimens somewhere between these extremes are most common. This does not preclude the possibility that some early and middle Miocene specimens from such offshore sandstone localities as Long Beach Shellbed, Clifden, Southland (Altonian, late early Miocene) belong in M. incertum.
The two specimens illustrated by Zittel (1865, pl. 10, figs 2a, b) appear to differ greatly in umbonal angle, but they are merely broken in different ways. The illustrated paralectotype, with less shell remaining (Zittel 1865, pl. 10, fig. 2b; Fig. 15E) has the dorsal margins more complete, whereas the lectotype (Zittel 1865, pl. 10, fig. 2a; Fig. 15B) has the dorsal margins and auricles broken away severely, and its ventral margin is a little incomplete. There is no doubt that the two specimens are conspecific. The lectotype is a moderately inflated right valve with six radial plicae, the central one subdivided into two. Each plica bears two to four prominent radial costae, and there are two or three narrower costae in each plical interspace. Examination under the microscope showed that the surface is entirely sculptured with narrow, rather widely spaced, commarginal grooves; the outer ends of the commarginal ridges are expanded into thin flanges perpendicular to the shell surface that meet at the grooves to form a false shell surface. No other microsculpture is visible, demonstrating that this species is correctly referred to Mesopeplum. The figured paralectotype is a weakly inflated left valve, again with six plicae. The second, unfigured paralectotype is severely abraded, with less than half the disc preserved. Its moderate inflation apparently indicates that it is a right valve.» 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. 34]
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Mesopeplum burnetti (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 12C, 13E, 15B, 15E.
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«1. Mesopeplum burnetti (Zittel, 1864): Hochstetter's type, described by Zittel, is from "Motupipi", i.e. Takaka Limestone, Golden Bay, West Nelson (Waitakian, Early Miocene). Differences from the Recent M. convexum are few, but comparison of large collections shows they are constant: Takaka Limestone specimens consistently have relatively weak plicae but prominent, coarse radial costae. Growth ledges are rarely present, and many specimens are of antero-posteriorly elongate shape, with a wide umbonal angle and a relatively weakly convex ventral outline. Specimens agreeing with these characters occur at a variety of localities throughout Miocene rocks of New Zealand, and are particularly common in the Tongaporutuan Patuahi Limestone near Gisborne (see below). The youngest specimens seen agreeing with M. burnetti are Kapitean (shellbed in cliffs at "the Whata" cave, Te Waewae Bay, Southland) although a single Opoitian specimen may be referable here (GS14939, C46/f150, shellbed in Rowallan Bum, Western Southland).»
BEU, A. G. 1995. Pliocene Limestones and their scallops. Lithostratigraphy, pectinid biostratigraphy, and paleogeography of eastern North Island late Neogene limestone. Institute of Geological & Nuclear Sciences Monograph, 10: 1-243, figs. 1-95. (New Zealand Geological Survey Paleontological Bulletin, 68). Institute of Geological and Nuclear Sciences, Ltd., Lower Hutt, New Zealand. [p. 52]
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«The range of variation of fossil taxa is in need of further study, and the number of valid species, and their time ranges, are unclear; the above synonymy assumes that at least the most common early-mid Cenozoic form (Mesopeplum burnetti) is part of the variation of M. convexum, but early-mid Cenozoic populations seem consistently to be relatively coarsely sculptured and could be distinct from Late Miocene-Recent populations. Modern specimens are exceedingly variable in the number and size of radial folds, the number and prominence of radial costae, the inflation and growth steps of the disc, and the shape of the disc; it seems possible that named extreme forms such as M. syagrus and M. waikohuense are also part of the variation of M. convexum.»
BEU, A. G. & P. A. MAXWELL. 1990. Cenozoic Mollusca of New Zealand. New Zealand Geological Survey Paleontological Bulletin, 58: 1-518, pls. 1- 57. [p. 338]
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