Glyptoxoceras torquatum Morton 1834 (TaxonConcept

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Species Glyptoxoceras torquatum Morton 1834

Diagnosis / Definition:

Cobban & Kennedy (1995):
DESCRIPTION.- Holotype, a slightly curved phosphatic internal mold of a body chamber 48.5 mm long, has maximum preserved whorl height of 13.5 mm, costal whorl breadth to height ratio of 0.9, and oval whorl section. Rib index 4, ribs distant, strong, narrower than interspaces. Ribs straight and markedly prorsiradiate on flank and strong on venter, which they cross in shallowest of convexities. Ribs weaken markedly on dorsum, where they are slightly concave. Four other fragments referred to the species are curved or straight; all have slightly compressed, oval whorl sections, and rib index of four. Imperfectly preserved suture has little-incised, bifid elements.

Discussion / Comments:

Cobban & Kennedy (1995):
TYPE.- The holotype, by monotypy, is ANSP 27864, the original of Morton, 1834, page 45, plate 15, figure 4, from Prairie Bluff, Alabama. MATERIAL.- Four specimens, USNM 463 127-463 130. DISCUSSION.- The nearly circular whorl section, coarse ribs and low rib index separate G. torquatum from all other Glyptoxoceras from the Prairie Bluff Chalk. Of other described species, there is a close resemblance to Glyptoxoceras largesulcatum (Forbes, 1846), recently revised by Kennedy and Henderson whorl breadth to height ratios of 0.84 to 0.9 and rib indices of 4.5 to 5; ribs have symmetrically concave interspaces and sharp crests; they become weakened and concave on the dorsum and feebly concave on the flank. The ribs of G. torquatum are thus blunter and more markedly prorsiradiate, but with so few Indian specimens known, it is possible that the two may be synonyms. OCCURRENCE.- Maastrichtian, Prairie Bluff Chalk at localities 33, 39 and 43, as well as at the type occurrence at Prairie Bluff, Alabama.

Systematics:

46
Ordo Ammonoidea
  Subordo Ancyloceratina
   Superfamilia Turrilitaceae
    Familia Diplomoceratidae
     Subfamilia Diplomoceratinae
      Genus Glyptoxoceras
       Species Glyptoxoceras torquatum

Synonym list:

Cobban & Kennedy (1995):

1834 Hamites torquatus Morton. - Morton : p.45 pl. 15; fig. 4

? 1846 Hamites large-sulcatus Forbes. - Forbes : p.117 pl. 11; fig. 1

? 1992 Glyptoxoceras largesulcatum Forbes. - Kennedy & Henderson : p.703 pl. 3, fig. 4-9; pl. 4, fig. 16-18; text-fig. 1D [with full synonymy]

1995 Glyptoxoceras torquatum Morton. - Cobban & Kennedy : p. 17, 19 fig. 11.1, 11.2, 11.18-11.26, 12.11

Stratigraphy - relative ages:

Maastrichtian: Cobban & Kennedy (1995)

References:

Morton,S.G.. (1834):
Synopsis of the Organic Remains of the Cretaceous Group of the United States.

Forbes,E.. (1846):
Report on the Cretaceous fossil invertebrates from southern India, collected by Mr. Kaye and Mr. Cunliffe . Transactions of the Geological Society of London Vol. 2(7) p. 97–174

Kennedy,W.J.. and Henderson,R.A.. (1992):
Heteromorph ammonites from the Upper Maastrichtian of Pondicherry, south India . Palaeontology Vol. 35 p. 693-731

Cobban,W.A.. and Kennedy,W.J.. (1995):
Maastrichtian ammonites chiefly from the Prairie Bluff Chalk in Alabama and Mississippi . Journal of Paleontology Vol. 69(5) p. 1-40

Anonymous: Unedited TaxonConcept data

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