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Species Anapachydiscus terminus | ||||||
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| Diagnosis / Definition: | ||||||
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Ward & Kennedy (1993): Diagnosis. - A large species of Anapachydiscus in which early and middle growth stages have 60 or more crowded flexuous prorsiradiate ribs per whorl. Description. - All specimens crushed, so that original whorl section cannot be reconstructed. To diameter of 120 mm, perhaps more, coiling very involute, with umbilicus comprising 20 percent of diameter, with 70 percent of previous whorl being covered. Ten to 12 primary ribs per half whorl arise at umbilical seam. Some strengthen into flat-topped bulla that is septate base of an umbilical spine to give 7-8 tubercles per half whorl. Tubercles give rise to pairs of ribs, while nontuberculate ribs that extend to umbilical shoulder may be single or branch into pairs. Shorter ribs intercalate both high and low on flank, to give total of 60 or more ribs per whorl. Ribs prorsiradiate, straight to feebly flexuous on inner to mid-flank, flexing forwards across ventrolateral shoulder where they are concave, crossing venter in broad convexity. Ribs increase in strength progressively across flanks, and are at maximum development on ventrolateral shoulders and venter, where they are narrow and rounded, and separated by somewhat wider interspaces. Umbilical bullae weaken from around 70 mm diameter, rib density increases with consequent crowding, and ribs may become flexuous.From 120mm diameter onwards, flank ribbing declines progressively, and early part of adult whorl ornamented by closely spaced ventrolateral and ventral ribs only. This ornament appears to weaken towards adult aperture in largest specimens, which are up to 350 mm in diameter. Sutures not seen. |
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| Discussion / Comments: | ||||||
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Ward & Kennedy (1993): Types.- Holotype is UWBM74501(Figure 39.2) from Member IV, Zumaya, Spain. Paratype UWBM76079 (Figure 40.9) is from Member IV, Bidart, France. Paratype UWBM76096 (Figure 41) is from Member IV, Hendaye, France. Etymology. - Terminus (Latin), the Roman deity who presided over boundaries or landmarks. Discussion. - Anapachydiscus terminus n. sp. differs from A. fresvillensis in the much higher rib density in early and middle growth stages (more than 60 vs. 31-32, increasingto 40). Later stages are very similar in that the massive involute shell of both species has ventral ribbing only, but flank ribs persist in A. terminus at a stage where they are effacing in A. fresvillensis (compare Figure 40.9 and Figure 35.6). The high rib density immediately distinguishes A. terminus from other European Campanian Anapachydiscus, such as A. wittekindi (Schlüter, 1872) (see Blaszkiewicz, 1980, p. 50, Pl. 42, figs. 1, 2, Pl. 43, fig. 2, Pls. 44-47, Pl. 48, figs. 3, 4, Pl. 49, figs. 1, 3, Pl. 50, figs. 2, 3, Pls. 51-53) and A. vistulensis Blaszkiewicz, 1980 (p. 48, Pl.42, figs. 3,4, Pl. 43, figs. 1, 3, P1.48, figs. 1, 2). The massive involute shell,higher whorls and crowded ribs immediately distinguish A. terminus from all other pachydiscids in the Biscay faunas. Pachydiscus (Pachydiscus)sersensis Atabekian and Akopian, 1969 (p. 17, Pl. 8, fig. 2, Pl. 10, fig. 1, Pl. 11, fig. 1) from the Maastrichtian sensu lato of Armenia is also said to occur in the upper upper Maastrichtian of the Vistula Valley, Poland (Machalski and Walaszczyk, 1988). The holotype is a composite internal mold of a phragmocone 237 mm in diameter, a cast of which is before us. There are an estimated 50-60 ribs at 200 mm diameter, but the inner whorls lack bullae or spines, ribbing is persistent, and much finer at large diameters than in A. terminus. Occurrence.- In the Biscay sections this taxon is short ranging, having been recovered from the top of Member IV (upper Maastrichtian) to the top of Member V (upper Maastrichtian). The species also occurs in the upper upper Maastrichtian of Denmark and in the Maastrichtian of Azerbaijan. |
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| Systematics: | ||||||
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38 Ordo Ammonoidea Subordo Ammonitina Superfamilia Desmocerataceae Familia Pachydiscidae Genus Anapachydiscus Species Anapachydiscus terminus |
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| Synonym list: | ||||||
| Ward & Kennedy (1993): 1979 Pachydiscus aff. colligatus Binkhorst. - BIRKELUND : p.56
1988 Pachydiscus colligatus Binkhorst. - Alizade et al. : p.379 pl. 27; fig. 6
1993 Anapachydiscus n sp. terminus . - Ward & Kennedy : p. 45, 46, 47 fig. 39.2, 40.1, 40.9, 41
1993 Anapachydiscus aff. fresvillensis Seunes. - BIRKELUND : p.49 pl. 4, fig. 3-6;
pl. 5;
pl. 6, fig. 1-4;
pl. 7
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| Stratigraphy - relative ages: | ||||||
| upper Maastrichtian: Ward & Kennedy (1993) |
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| References: | ||||||
BIRKELUND,T.. (1979): Alizade,A..; Aliev,G.A..; Aliev,M.M..; Aliyulla,K.. and Khaliev,A.G.. (1988): Ward,P.D.. and Kennedy,W.J.. (1993): BIRKELUND,T.. (1993): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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