Glyptoxoceras indicum Forbes 1846 from: Kennedy, W.J..Henderson, R.A.. (1992): Heteromorph ammonites from the Upper Maastrichtian of Pondicherry, south India . Palaeontology Vol. 35 p. 693-731
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Species Glyptoxoceras indicum Forbes 1846
|Diagnosis / Definition:
Kennedy & Henderson (1992):
The early whorls (pl. 2, figs. 1, 4-5, 7, 9) are in the form of a very low helix, with a total diameter to the spire of 22 mm, the translation rate being very low. The whorl section is circular at this stage, with coarse , blunt ribs, seperated by somewhat wider interspaces, and a rib index of 6-7. Ribs are weakest on the inner whorl face, feebly rursiradiate, strenghtening and strongly rursiradiate on the upper whorl face, strongest and markedly prorsiradiate on the outer whorl face and weakened and feebly convex on the lower. The lectotype (Pl. 2, figs. 3.12-13) is a 35 mm long, entirely body chamber, consisting of the external mould of a smaller, straight shaft, connected by a stongly curved portion to a longer, straight shaft. The maximum preserved whorl height is 7 mm, the whorl section circular, the rib index 7. Ribs are strong, sharp and narrower than the interspaces. They are feebly prorsiradiate on the flanks of the shaft, and pass straight across the venter, but change to markedly rursiradiate on the hook. BMNH C51111 (Pl. 1, figs. 3-4) is more complete, consisting of the displaced fragments of straight shaft, a curved sector and a second, shorter, straight shaft, the whole forming an asymmetric U. The specimen is partly crushed, but where well preserved, has a maximum whorl height of 12 mm, and a whorl breadth to height ratio of 0.96. The ribbing style is comparable to that of the lectotype; feebly prorsiradiate on the smaller shaft, becoming markedly rursiradiate on the hook and large shaft, but the rib index, 9, is slightly higher on the final shaft. There is a prominent constriction and terminal collar at the aperture, suggesting the specimen to be adult.
|Discussion / Comments:
Kennedy & Henderson (1992):
The lectotype, by the subsequent designation of Matsumoto (1959a, p. 167), is BMNH C 51113, the original of Kossmat (1895, pl. 19(5), fig. 4), GSC R10496. Paralectotypes include a part of the lectotype of G. rugatum, BMNH C51100, the original of Forbes (1846, pl. 11, fig. 4a, c); BMNH C51111, the original of Kossmat (1895, pl. 19 (5), fig. 7a-b), GSC R105000, referred by Kossmat to G. rugatum. Possible paralectotypes are BMNH C51130, C51132-51134, C51136, C51138 that belong to the present species; other possible paralectotypes are referred to G. rugatum and G. largesulcatum under these species; all from the Valudavur Formation of Pondicherry, south India. Topotypes are BMNH C4050 (2 fragments), C51117, and C82502-82503 (ex Marsham Collection).
Forbes (1846, pl. 11, fig. 4a-c) figured only a fragment of what has been subsequently designated the lectotype of G. rugatum to illustrate the species indicus. Stoliczka (1866, pl. 85, figs. 1-5) used the name, but none of his figured specimen belong to the species as defined here. Kossmat (1895) pointed out that the specimen figured by Forbes as indicum was identical to Forbes's Hamites subcompressus (they were shown by Phillips (1977, p. 124) to be based on bits of the same specimen), and figured a syntype of Forbes's indicus (1895, pl. 19 (5), fig. 4a-b; pl. 2, figs. 3, 12-13) as well as a syntype of Forbes’s rugatus (Kossmat, 1895, pl . 19 (5), fig. 7; Pl. 1, figs. 3-4) which we identify with Glyptoxoceras indicum. Shimizu (1935) considered Forbes’s figured specimen to be the holotype of indicum, but Matsumoto (1959a, p. 167) correctly recognized (following Kossmat, 1895, p. 145(49))that Hamites indicus of Forbes was based upon a number of syntypes, and designated BMNH C51113, the original of Kossmat, 1895 (pl. 19 (5), fig. 4a-b; pl. 1, figs. 3-4) as lectotype. So defined, G. indicum is a distinctive species, characterized by the presence of an initial helix, followed by a single elliptical whorl, beautifully illustrated by examples from the Maastrichtian of California (Matsumoto 1959a, pl. 41, figs. 2-6). The coiling style immediately separates G. indicum from G. rugatum and G. largesulcatum, while G. tenuisulcatum, with similar coiling, has a much higher rib index, the ribs oblique on the venter of shafts rather than transverse, and reaches a much larger size (Pl. 2, figs. 2, 6, 8, 30).
The Glyptoxoceras indicum of Brunnschweiler (1966, p. 44, pl. 6, figs. 1-3; text-fig. 28) is G. rugatum. Diplomoceras indicum oestosulcatum Collignon, 1969 (p. 45, pl. 530, fig. 2090), from the Lower Campanian of Madagascar, is based on a straight shaft 80 mm long, a coiling style quite unlike that of G. indicum. The Santonian-Campanian fragments from Zululand and Pondoland (Woods 1906, pl. 44, fig. 2; Klinger 1976, pl. 34, figs. 3, 5) are intermediate. The Diplomoceras (Glyptoxoceras) indicum of Immel et al. (1982, pl. 10, figs. 5-6) from the Santonian of Austria are of uncertain affinities in our view, being densely ribbed curved fragments only. The Glyptoxoceras subcompressum of Ward and Westermann (1976, text-figs. 1-3) and Ward (1976, pl. 1, figs. 1-5; text-fig. 3) consists of an initial helix, followed by one and a half elliptical whorls, rather as in G. indicum, but the plane of coiling of the helix is 90° to that of the late whorls.
Maastrichtian of south India and California.
Species Glyptoxoceras indicum
|Kennedy & Henderson (1992):
p 1846 Hamites indicus Forbes. - Forbes
: p.116 [non pl. 11; fig. 4 (=G. rugatum Forbes, 1846)]
non 1847 Hamites indicus Forbes. - d'Orbigny
: pl. 3; fig. 13-14 [?=Diplomoceras cylindraceum Defrance, 1816]
1954 Glyptoxoceras Spath. - Wright & Matsumoto : text-fig. 5
non 1966 Glyptoxoceras indicum Forbes. - BRUNNSCHWEILER
: p.44 pl. 6, fig. 1-3;
text-fig. 28 [=G. rugatum]
1992 Glyptoxoceras indicum Forbes. - Kennedy & Henderson
: p. 697, 701 pl. 1, fig. 3-4;
pl. 2, fig. 1, 3-5, 7, 9, 12-13
|Was used in synonym list of:
|Stratigraphy - relative ages:
| Maastrichtian: Kennedy & Henderson (1992)
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Kennedy,W.J.. and Henderson,R.A.. (1992):
Heteromorph ammonites from the Upper Maastrichtian of Pondicherry, south India . Palaeontology Vol. 35 p. 693-731
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