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Species Pachydiscus (Pachydiscus) epiplectus Redtenbacher 1873 | ||||||
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| Diagnosis / Definition: | ||||||
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Ward & Kennedy (1993): Description. - "The whorl section varies from compressed to depressed, sometimes on the same specimen, due to post-mortem crushing, with a small deep umbilicus, the umbilical wall and shoulder rounded. The inner flanks are inflated, the outer flanks flattened and convergent, with a broadly rounded venter. The greatest breadth is below mid-flank. Primary ribs arise at the umbilical shoulder, singly or in pairs, from feeble bullae or not and are narrow, sharp and prorsiradiate, separated by wide interspaces. They sweep forwards across the inner flank, while intercalated ribs are inserted at various points high or low on the flank to give an estimated 20-22 bullae at the umbilical shoulder and a total of 50-55 ribs per whorl at a diameter of 100-1 50 mm. The ribs appear slightly flexuous in some specimens (due to post-mortem distortion?) but all sweep forwards over the ventrolateral shoulders where they are markedly concave, and pass across the venter in a broad convexity. The bestpreserved of the larger specimens . . . is distorted, with a major diameter of 220 mm. It shows the same style of ornament persisting to around 170 mm, beyond which it is poorly preserved, although flank ribs persist and there is strong ventral ribbing, the rib density being an estimated 60 per whorl. In the largest specimen . . . the ribbing appears to be effaced on the mid-flank region." (Kennedy and Summesberger, 1986, p. 192.) The Biscay specimens are crushed flat, a less misleading deformation than that shown by the Austrian material (e.g., Figure 23.4, 23.5). A typical juvenile is shown in Figure 30.5, and illustrates the ornament at this stage. There are an estimated total of 55-60 ribs per whorl, long primaries arising at umbilical shoulder, and variably bullate, with one or two intercalated ribs arising low on flank. These juveniles co-occur with much larger specimens that show weakening flank, but persistent ventral ornament to diameters of at least 250 mm. |
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| Discussion / Comments: | ||||||
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Ward & Kennedy (1993): Type. - Lectotype, by subsequent designation by Kennedy and Summesberger, 1986, p. 192, is No. 1868.X. 14, in the collections of the Institute of Geology of Vienna University, the original of Redtenbacher, 1873, p. 121, P1. 28, fig. la, b, from Muthmannsdorf in the Neue Welt Basin, Austria. Discussion.- This has been a poorly known species, recently revised by Kennedy and Summesberger (1 986). It is easily distinguished from other Biscay species, such as Pachydiscus (P.) neubergicus, P. (P.) gollevillensis and P. (P.) armenicus, by the much more involute, massive, relatively high-whorled Nautilus-like shell. This gross shell mo~hologiys matched by Anapachydiscus terminus n. so., to be described below. Juveniles are easily separated by the pronounced umbilical bullae and much fine;, denser ribs of terminus, which commonly arise in pairs from bullae at the umbilical shoulder, while adults have weak or no flank ribbing. Differences from other P. (Pachydiscus) species are discussed by Kennedy and Summesberger (1 986). The other common pachydiscid in the Biscay faunas is Anapachydiscus fresvillensis (Seunes, 1 890a) (Figure 36.1,36.2). This has a similarly massive shell, but juveniles can be distinguished, when well preserved, by the presence of strong umbilical spines corresponding to prominent flat-topped umbilical bullae on molds. There are generally only around 1 1-12 such spines/bullae per whorl, and around 30 ribs. Bullae weaken from 60 mm diameter or so, and migrate out to an inner flank position, thereafter declining, as does flank ribbing, leaving an adult shell ornamented by coarse rounded ventrolateral and ventral ribs, numbering 40 per whorl. Occurrence. - In the Biscay sections this taxon is found low in Member I (lower Maastrichtian). The types are from the lower Maastrichtian of the Neue Welt Basin in Austria, and the species is also known from the lower Maastrichtian of Neuberg, Steiermark, Austria, the former USSR, and Bulgaria. It may also be present at Tercis, Landes, France, and in Madagascar. |
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| Systematics: | ||||||
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38 Ordo Ammonoidea Subordo Ammonitina Superfamilia Desmocerataceae Familia Pachydiscidae Genus Pachydiscus Subgenus Pachydiscus Species Pachydiscus (Pachydiscus) epiplectus |
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| Synonym list: | ||||||
| Ward & Kennedy (1993): 1873 Ammonites epiplectus Redtenbacher. - Redtenbacher : p.121 pl. 28; fig. 1
1986 Pachydiscus (Pachydiscus) epiplectus Redtenbacher. - Kennedy & Summesberger : p.192 pl.6, fig. 3,4;
pl. 7, figs. 1,2;
pl. 8, fig. 1, 2;
pl. 9;
pl. 10, fig. 1-3;
pl. 11, fig. 14;
pl. 12;
pl. 13, fig. 1-3 (with full synonymy)
1993 Pachydiscus (Pachydiscus) epiplectus Redtenbacher. - Ward & Kennedy : p. 33, 36, 41, 46 fig. 28.4, 28.5, 30.5, 35.1, 35.2, 35.4, 40.4
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| Stratigraphy - relative ages: | ||||||
| lower Maastrichtian: Ward & Kennedy (1993) |
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| Specimen: | ||||||
| Collections of the Institute of Geology of Vienna University, Inventory number: No. 1868.X.14 |
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| References: | ||||||
Redtenbacher,A.. (1873): Kennedy,W.J.. and Summesberger,H.. (1986): Ward,P.D.. and Kennedy,W.J.. (1993): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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