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Species Maorites weddelliensis Macellari 1986 | ||||||
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| Diagnosis / Definition: | ||||||
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MACELLARI (1986): DIAGNOSIS.- Umbilical wall almost vertical. Whorl section relatively inflated. Omamentation composed of slightly prorsiradiate, widely spaced ribs (four ribs in one cm at H = 3 cm). Prominent tubercles formed at the conjunction of two ribs in the umbilical margin. Deep straight constrictions intersect 2-4 previous ribs. DESCRIPTION.- Medium-sized shell, moderately involute (U/D = 32-33), of moderately inflated whorl section (W/H = 0.70- 0.79) (Table 12), with flat flanks and broadly rounded venter. Umbilical wall almost vertical. Ornamentation composed of widely spaced ribs that are slightly prorsiradiate on the dorsal flank but rectiradiate on the ventral flank and venter. Young portion of shell usually also displaying widely spaced radial ribs. Ribs bifurcate in the middle of the flank. A prominent, slightly radially elongated tubercle is formed at the junction of two ribs in the umbilical margin. Approximately 11 tubercles are present in the last whorl. Ribs become more prominent, wider and more spaced in the living chamber. Five deep constrictions, intersecting 2-4 previous ribs, are observed in the last whorl. The adapical border of the constriction is thicker and more elevated than the adoral border. Suture line not observed. |
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| Discussion / Comments: | ||||||
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MACELLARI (1986): HOLOTYPE.- 0SU 38260 (Figures 34.2- 34.4). MATERIAL.- Six specimens, two of them very well preserved. ORIGIN OF NAME.- Named after the nearby Weddell Sea. REMARKS.- This species was originally included with doubts in the subgenus Kossmaticeras (Natalites) Collignon (Macellari, 1984b), mostly because of its resemblance to K. (Natalites) sulcatum (Marshall) (in Henderson, 1970, Pl. 5, figs. 1a, b). The subgenus K. (Natalites) Collignon is characterized by its strong umbilical tubercles and almost straight and prominent ribs which are continuous throughout the flank (cf. Collignon, 1955, p. 13; Matsumoto, 1955, p. 142 [under Kaiparaites]; and Riccardi, 1983). Even though the radial ribs in Maorites weddelliensis are relatively straight, they are not as strong as in typical K. (Natalites). K. (Natalites) sulcatum (Marshall) (in Henderson, 1970, P1. 5, figs. la, b) displays the typical Maorites ornamentation, with ribs prorsiradiate in the flank and rectiradiate with intercalary ribs in the upper flank. Ribs in this species are also weak for K. (Natalites). It is considered that this specimen should be classified as Maorites sulcatus (Marshall). M. sulcatus resembles M. subtilistriatus Collignon from the lower Campanian of Madagascar (Collignon, 1955) in the inflation of the whorl section. Maorites weddelliensis is almost identical in lateral view to M. sulcatus. They differ, however, in the degree of inflation (W/H = 0.70-0.79 in the former and W/H = 0.85- 0.94 in the latter), and in the larger size of the Antarctic specimens. K. (Natalites) natalensis (Spath) (in Spath, 1922, p. 34, P1. 5, fig. 3) from the Umzamba Beds of Pondoland, South Africa, has a similar degree of involution and ribbing pattern. However, the ribs of K. (Natalites) natalensis are more conspicuous and slightly more prorsiradiate, and the constrictions instead of being radial are strongly projected forward. Moreover, the umbilical tubercles are more prominent and the whorl section is slightly more inflated than in M. weddelliensis (W/H = 0.8 1 vs. 0.70- 0.79). Maorites weddelliensis differs from M. seymourianus by its more inflated cross section (Figures 25.2-25.3), straight and less numer- ous ribs, more prominent umbilical tubercles, and more incised constrictions. LOCALITIES.- Seymour Island, 4 1, 143, 174, 423, M-84, H'. STRATIGRAPHIC DISTRIBUTION.- Lopez de Bertodano Formation, Pachydiscus ootacodensis Zone (lower Maastrichtian). |
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| Systematics: | ||||||
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50 Ordo Ammonoidea Subordo Ammonitina Superfamilia Desmocerataceae Familia Kossmaticeratidae Subfamilia Kossmaticeratinae Genus Maorites Species Maorites weddelliensis |
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| Synonym list: | ||||||
| MACELLARI (1986): 1985 Kossmaticeras? (Natalites) n sp. sp. . - MACELLARI : p.225
1986 Maorites n sp. weddelliensis Macellari. - MACELLARI : p. 29, 40 fig. 25.3, 34.1-34.5
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| Stratigraphy - relative ages: | ||||||
| lower Maastrichtian: MACELLARI (1986) |
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| References: | ||||||
MACELLARI,C.E.. (1985): MACELLARI,C.E.. (1986): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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