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Pachydiscus (Neodesmoceras) mokotibense Collignon 1952 from: Kennedy, W.J.. (1986): The ammonite fauna of the Calcaire Baculites (Upper Maastrichtian) of the Cotentin Peninsula (Manche, France) . Palaeontology Vol. 29(1) p. 25-83
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Species Pachydiscus (Neodesmoceras) mokotibense Collignon 1952



Alternative name:
Diagnosis / Definition:
Kennedy (1986):
Type. Holotype by original designation is the original ofCollignon (1952, pl. 28, fig. 2; 1955, pI. 27, fig. 2), from the Maastrichtian of Mokotibe, Madagascar. There are also four paratypes, all in the EMP Collections. Material. SP unreg., from the Fosse de la Bonneville.Description. The specimen is a wholly septate internal mould some 140 mm in diameter. Coiling involute, umbilicus comprising approximately 20% of diameter. Whorl section as broad as high. Inner flanks broadly rounded, outer flanks flattened, convergent, ventrolateral shoulder and venter broadly rounded. There are traces of narrow, distant ribs on outer flank and venter at smallest diameter visible, thereafter lost. Suture line intricately subdivided.
Discussion / Comments:
Kennedy (1986):
Discussion. Neodesmoceras covers a range of Pachydiscus in which ornament is lost at an early stage, leaving the shell almost smooth. The present specimen is the first European representative of the subgenus, previously known only from the Indo-Pacific region (Madagascar, Zululand, Japan, Alaska, California). Its nearly equidimensional whorl seetion easily distinguishes it from P. (N.) japonicus, P. (N.) obsoletiformis Jones, 1963 (p. 40, pI. 26, figs. 1,4-8; pIs. 27 and 28; text-figs. 20 and 22A), P. (N.) gracilis Matsumoto, 1979 (p. 60, pI. 10, figs. 1-3; pI. 11, fig. 1; pI. 12, fig. 2; text-fig. 6), and P. (N.) catarinae (Anderson and Hanna, 1935) (p. 19, pI. 11, fig. I; pI. 2, fig. 1; pI. 3, figs. 1-3). Its overall proportions correspond to those of P. (N.) mokotibense Collignon, 1952 (p. 81, pI. 28, fig. 2; republished by Collignon 1955, p. 75, pI. 27, fig. 2; see also Collignon 1971, p. 32, pI. 653, fig. 2410), while comparison with the types (EMP unreg.) and Zululand specimens referred to the species (BMNH C90180-90189) confirms this view. In particular the African material shows periodic distant ventral ribs during early growth, as is seen in the present specimen at the smallest diameter visible.
Systematics:

39
 Ordo Ammonoidea
  Subordo Ammonitina
   Superfamilia Desmocerataceae
    Familia Pachydiscidae
     Genus Pachydiscus
      Species Pachydiscus (Neodesmoceras) mokotibense
       Species Pachydiscus sumneri
Synonym list:
Kennedy (1986):
1952 Pachydiscus mokotibense Collignon. - COLLIGNON : p.81 pl. 28, fig. 2
1955 Pachydiscus mokotibense Collignon. - COLLIGNON : p.75 pl. 27, fig. 2
1971 Pachydiscus mokotibense Collignon. - COLLIGNON : p.32 pl. 653, fig. 2410
1986 Pachydiscus (Neodesmoceras) mokotibense Collignon. - Kennedy : p.40 text-fig. 5
Was used in synonym list of:
Stratigraphy - relative ages:
upper Maastrichtian - Maastrichtian: Kennedy (1986)
References:

COLLIGNON,M.. (1952):
Ammonites neocretacees du Menabe (Madagscar). II-Les Pachydiscidae. . Trav. Bur. geol. Madagascar Vol. 41 p. 144 pp.

COLLIGNON,M.. (1955):
Ammonites neocretacees du Menabe (Madagascar). II-Les Pachydiscidae. . Annls geol. Servo Mines Madagascar Vol. 21 p. 98 pp.

COLLIGNON,M.. (1971):
Atlas des fossiles caracteristiques de Madagascar (Ammonites)(Maestrichtian). Vol. 17 p. 82

Kennedy,W.J.. (1986):
The ammonite fauna of the Calcaire Baculites (Upper Maastrichtian) of the Cotentin Peninsula (Manche, France) . Palaeontology Vol. 29(1) p. 25-83

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