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Species Pachydiscus (Neodesmoceras) mokotibensis Collignon 1952



Alternative name:
Pachydiscus mokotibensis Collignon 1952
Diagnosis / Definition:
Kennedy & Cobban (1996):
DESCRIPTION.- Specimens have whorl heights of between 13.5 and 45 mm, and there are pieces of much larger whorls; all are wholly septate. Coiling very involute, with small, deep umbilicus with broadly rounded umbilical wall, umbilical shoulder more narrowly rounded. Whorl section compressed, with whorl breadth to height ratio of 0.94 at whorl height of 20.7 mm., and 0.84 at whorl height of 38 mm. Flanks flattened, convergent, ventrolateral shoulders, venter broadly rounded. Ornament consists of weak, narrow, widely separated straight to feebly flexuous flank ribs that strengthen across outer flank, where they are feebly concave, to cross venter in a very shallow convexity. Suture line is deeply, intricately subdivided, typical for genus.
Landman et al. (2007):
DESCRIPTION.- MAPS A2002g2 is a large internal mold consisting of one septate whorl and a fragment of the body chamber, both of which fit together (figs. 26, 27). The specimen is smooth without any ornament. The diameter of the septate piece is 151 mm. The whorl width and height at the adoral end of the phragmocone are 34.8 and 87.3 mm, respectively; the ratio of whorl width to height is 0.40. The inner flanks are nearly flat and slightly divergent, the midflanks are broadly rounded and subparallel, and the outer flanks are nearly flat and converge to an acute venter. The maximum whorl width of the piece of body chamber is approximately 62 mm. The venter is more rounded than it is on the phragmocone. There are several circles on the left side (not illustrated), exposing the matrix below. These circles may represent the sites of limpet attachment or punctures produced by a mosasaur bite. The suture has narrow-stemmed saddles with phylloidlike terminations (fig. 28).
Discussion / Comments:
Kennedy & Cobban (1996):
TYPES.- Holotype by original designation is the original of Collignon, 1952, plate 28, figure 2; 1955, plate 28, figure 2, from the Maastrichtian of Mokotibe, Madagascar; there are four paratypes, from the same horizontal and locality; all the types are housed in the École des Mines Collections, now in the Université Claud Bernard, Lyon. DISCUSSION.- The holotype of P. (N.) mokotibensis (Collignon, 1952, plate 28, figure 2; 1955, plate 28, figure 2) is a completely smooth individual 140 mm in diameter. Juveniles of the species from Zululand (South Africa) in the British Museum (Natural History)and Oxford University Museum collectionshave widely spaced narrow ribs, as in the present material. MATERIAL.- NJSM 11284a-e, in total 14 fragmentary molds from the main fossiliferous layer of the Hornerstown Formation at the Inversand Marl Pit, Sewell, Gloucester County, New Jersey. OCCURRENCE.- Upper Maastrichtian of Madagascar,Zululand (South Africa); the Cotentin Peninsula, Manche, France; and the base of the Hornerstown Formation in New Jersey.
Landman et al. (2007):
TYPE.- The holotype, from Noxubee County, Mississippi, is lost (fide Stephenson, 1941: 434). MATERIAL.- Two specimens: MAPS A2002g1 and A2002g2 from the Pinna Layer from the top of the Tinton Formation, AMNH loc. 3335, Manasquan River Basin, central Monmouth County, New Jersey. OCCURRENCE.- Pinna Layer, top of the Tinton Formation, Manasquan River Basin, central Monmouth County. This species also occurs in the Tinton Formation, near Tinton Falls, northeastern Monmouth County (Weller, 1907; Reeside, 1962; Gallagher, 1993; Landman et al., 2004b); the upper part of the Navesink Formation and the lower part of the New Egypt Formation in the Crosswicks Creek Basin, southwestern Monmouth County (Landman et al., in prep.); and at the Inversand Marl Pit, Gloucester County (Gallagher, 1993; Kennedy et al., 1995; Kennedy and Cobban, 1996). Specimens of Sphenodiscus occur in the top of the New Egypt Formation and as reworked material at the base of the Hornerstown Formation at Parkers Creek, northeastern Monmouth County, but they are too fragmentary for specific identification (Landman et al., 2004b). Elsewhere on the Gulf and Atlantic Coastal Plains, this species is known from the Corsicana Formation in northeast Texas (Kennedy and Cobban, 1993); the upper part of the Ripley Formation in Mississippi; the Prairie Bluff Chalk in Alabama and Mississippi (Cobban and Kennedy, 1995); the Providence Sand in the Chattahoochee River area, Alabama and Georgia; the upper part of the Peedee Formation in North Carolina (Landman et al., 2004a); and the Severn Formation in Prince Georges County, Maryland (Kennedy et al., 1997). It also occurs in the Escondido Formation in Trans-Pecos Texas and northern Mexico (Stephenson, 1941, 1955). In the Western Interior, this species occurs in the Hoploscaphites nicolletii and Jeletzkytes nebrascensis Zones of the Fox Hills Formation in north-central South Dakota (Landman and Waage, 1993) and in the J. nebrascensis Zone of the Pierre Shale in southeastern South Dakota and northeastern Nebraska (Kennedy et al., 1998).
Systematics:

45
 Classis Cephalopoda
  Subclassis Nautiloidea
   Ordo Ammonoidea
    Subordo Ammonitina
     Superfamilia Desmocerataceae
      Genus Pachydiscus
       Subgenus Neodesmoceras

48
  Ordo Ammonoidea
   Subordo Ammonitina
    Superfamilia Desmocerataceae
     Familia Pachydiscidae
      Familia Sphenodiscidae
       Genus Pachydiscus
        Genus Sphenodiscus
         Subgenus Neodesmoceras
          Species Pachydiscus (Neodesmoceras) mokotibensis
Synonym list:
Kennedy & Cobban (1996):
1952 Neodesmoceras mokotibense Collignon. - COLLIGNON : p.81 pl. 28; fig. 2
1955 Neodesmoceras mokotibense Collignon. - COLLIGNON : p.75 pl. 28; fig. 2
1971 Neodesmoceras mokotibense Collignon. - COLLIGNON : p.32 pl. 653; fig. 2410
1986 Neodesmoceras mokotibense Collignon. - Kennedy : p.40 text-fig. 5
1996 Pachydiscus (Neodesmoceras) mokotibensis Collignon. - Kennedy & Cobban : p.800 fig. 2.7-2.12, 2.15-2.18
Landman et al. (2007):
1952 Neodesmoceras mokotibense Collignon. - COLLIGNON : p.81 pl. 28; fig. 2
1955 Neodesmoceras mokotibense Collignon. - COLLIGNON : p.75 fig. 21; pl. 28, fig. 2
1971 Pachydiscus (Neodesmoceras) mokotibensis Collignon. - COLLIGNON : p.32 pl. 653; fig. 2410
1986 Pachydiscus (Neodesmoceras) mokotibense Collignon. - Kennedy : p.40 text-fig. 5
1996 Pachydiscus (Neodesmoceras) mokotibensis Collignon. - Kennedy & Cobban : p.799 fig. 2.7-2.12, 2.15-2.18
2006 Pachydiscus (Neodesmoceras) mokotibense Collignon. - Kennedy & KLINGER : p.150 fig. 125-140
2007 Pachydiscus (Neodesmoceras) mokotibensis Collignon. - Landman et al. : p. 59, 60 fig. 24, 25
Stratigraphy - relative ages:
upper Maastrichtian: Kennedy & Cobban (1996)
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 ŕ Baculites (Upper Maastrichtian) of the Cotentin Peninsula (Manche, France) . Palaeontology Vol. 29(1) p. 25-83

Kennedy,W.J.. and Cobban,W.A.. (1996):
Maastrichtian ammonites from the Hornerstown Formation in New Jersey . Journal of Paleontology Vol. 70(5) p. 798–804

Kennedy,W.J.. and KLINGER,H.C.. (2006):
Cretaceous faunas from Zululand and Natal, South Africa. The ammonite family Pachydiscidae Spath, 1922 . African Natural History2 (2006) p. 17-166

Landman,N.H..; Johnson,R.O..; Garb,M.P..; Edwards,L.E.. and Kyte,F.T.. (2007):
Cephalopods from the Cretaceous/Tertiary Boundary Interval on the Atlantic Coastal Plain, with a Description of the Highest Ammonite Zones in North America; Part III; Manasquan River Basin, Monmouth County, New Jersey . Bulletin of the American Museum of Natural History Vol. 303 p. 1-122

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