Pachydiscus jacquoti jacquoti Seunes 1890 (TaxonConcept

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Subspecies Pachydiscus jacquoti jacquoti Seunes 1890

Alternative name:

Pachydiscus (Pachydiscus) jacquoti jacquoti Seunes 1890

Diagnosis / Definition:

Ward & Kennedy (1993):
Description. - Biscay specimens range up to 150 mm in diameter, and are commonest pachydiscid in fauna. Coiling moderately evolute, with around 40 percent of previous whorl covered. Whorls expand slowly; umbilicus comprises around 30 percent of diameter. Juvenile shell smooth as can be seen from inner whorls of large specimens, with ornament first appearing at estimated diameter of 15 mm. Distant bullae, around eight per whorl, are first ornament to appear, but by diameter of 80- 90 mm there are up to 14 bullae that give rise to narrow, distant, straight prorsiradiate ribs that weaken markedly on outer flank, flex forwards and cross venter in broad convexity. Ribs occasionally branch in pairs from bullae, or intercalate so that there are just over twice as many ventral ribs as umbilical bullae. Beyond 90 mm, bullae may decline as do secondary ribs, leaving ornament of primary ribs only, weakened markedly over venter.

Discussion / Comments:

Ward & Kennedy (1993):
Types. - Seunes figured three specimens (1890a, PI. 3(2), figs. 1-3) and mentioned others, from the Calcaire a Baculites of the Cotentin Peninsula, Manche, France, Pyrénées-Atlantiques and NW of Alcoy, Spain. The original of his Pl. 3(2), fig. 1 should be designated lectotype, when found (see discussion in Kennedy, 1986c, p. 36). Discussion.- Coiling, whorl section (when uncrushed), and distant, sparse ribbing render Pachydiscus jacquoti jacquoti easily distinguishable from all of the other pachydiscids in the Biscay fauna; differences are discussed in detail by Kennedy (1986c, p. 36). Pachydiscus (P.) llareni Wiedmann, 1960 (p. 764, Pl. 4, fig. 6, Pl. 5, fig. 4) is no more than a crushed P. (P.) jacquoti jacquoti in our view. Pachydiscus jacquoti australis Henderson and McNamara, 1985 (p. 76, Pl. 8, figs. 1, 2, 7-10, text-figs. 12a, 13b, 14, 15a) differs from the nominate subspecies in retaining secondary ribs to maturity, whereas they are lost in the former. Pachydiscus (P.) jacquoti chilensis Stinnesbeck, 1986 (p. 2 18, Pl. 13, fig. 8, Pl. 1 5, figs. l,3, text-fig. 28a) was differentiated from the nominate subspecies on the basis of possessing 22-26 ribs per whorl. The holotype is a massive shell, distinguished by its coarse ribbing, unlike that of the present material. Occurrence.- In the Biscay sections this taxon ranges from near the top of Member I to the top of Member V. Elsewhere, the nominate subspecies is restricted to the upper Maastrichtian with records from the area between Gan and Rébénacq, Pyrénées- Atlantiques, Tercis, Landes, the Calcaire a Baculites of the Cotentin Peninsula, Manche, all in France; Kunrade, the Netherlands, Armenia, and Madagascar.

Systematics:

38
Ordo Ammonoidea
  Subordo Ammonitina
   Superfamilia Desmocerataceae
    Familia Pachydiscidae
     Genus Pachydiscus
      Subgenus Pachydiscus
       Subspecies Pachydiscus jacquoti jacquoti

Synonym list:

Ward & Kennedy (1993):

1890 Pachydiscus jacquoti Seunes. - Seunes : p.5 pl. 3(2); fig. 1-3

1960 Pachydiscus (Pachydiscus) llareni Wiedmann. - Wiedmann : p.764 pl. 4, fig. 6; pl. 5, fig. 4

1964 Pachydiscus (Pachydiscus) llareni Wiedmann. - Wiedmann : p.147 fig. 39

1986 Pachydiscus (Pachydiscus) jacquoti Seunes. - Kennedy : p.34 pl. 5, fig. 3-11, 15-19; pl. 6, text-fig. 2d, e, 3o, s, 4b (with full synonymy)

1986 Pachydiscus (Pachydiscus) jacquoti Seunes. - Kennedy : fig. 9a, b

1987 Pachydiscus (Pachydiscus) jacquoti Seunes. - Kennedy : p.171 pl. 11, figs. 1-4; pl. 12, figs. 1-3, 8-10; pl. 13, fig. 1-5; pl. 14, fig. 4-6, 8-10; pl. 15, fig. 1-3, 12, 13; text-fig. 7b

1993 Pachydiscus jacquoti jacquoti Seunes. - Ward & Kennedy : p. 27, 35, 36, 37, 4 fig. 25.8, 25.13, 29.1-29.4, 30.1-30.3, 31.2, 31.3, 31.6, 35.7, 39.4, 40.2

Stratigraphy - relative ages:

lower Maastrichtian - upper Maastrichtian: Ward & Kennedy (1993)

References:

Seunes,J.. (1890):
Recherches géologiques sur les terrains secondaires et l' Eocene inferieur de la region sous-pyrénéene du sud-ouest de la France (Basses-Pyrenees et Landes). p. 250 pp.

Wiedmann,J.. (1960):
Le Crétacé supérieur de l'Espagne et du Portugal et ses céphalopodes . C. R. du Congrés des Sociétés Savantes-Dijon, 1959; Colloque sur le Crétacé supérieur francais p. 709-764

Wiedmann,J.. (1964):
Le Crétacé supérieur de l'Espagne et du Portugal et ses céphalopodes . Estudios Geologicos Instituto Lucas Mallada Vol. 20 p. 107-148

Kennedy,J.W.. (1986):
The Campanian-Maastrichtian ammonite sequence in the environs of Maastricht (Limburg, the Netherlands) . Newsletters on Stratigraphy Vol. 16 p. 149-168

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

Kennedy,W.J.. (1987):
The ammonite faunas of the type Maastrichtian, with a revision of Ammonites colligatus Binkhorst, 1861 . Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre Vol. 56 p. 151-267

Ward,P.D.. and Kennedy,W.J.. (1993):
Maastrichtian Ammonites from the Biscay Region (France, Spain) . Memoir (The Paleontological Society), Journal of Paleontology34 (Supplement to Vol. 67)(5) p. 1-58

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