versión On-line ISSN 1816-8396
Afr. nat. history (Online) vol.7 Cape Town ene. 2011
William James KennedyI; Herbert Christian KlingerII
IDepartment of Earth Sciences, Oxford University, South Parks Road, Oxford OX1 3AN, U.K. E-mail: email@example.com
IINatural History Collections Department, Iziko South African Museum, P.O. Box 61, Cape Town, 8000 South Africa. E-mail: firstname.lastname@example.org
The ammonite genus Grandidiericeras Collignon, 1961 was previously known from two species, based on six described specimens, three of which, referred to Grandidiericeras grandidierorum Collignon, 1961, are from the Middle Campanian of Madagascar, and three, referred to Grandidiericeras nagaoi Matsumoto & Saito, 1987, from the Coniacian of Japan. A single specimen from the Upper Santonian to Lower Campanian of Lake St Lucia in KwaZulu-Natal represents a new species, Grandidiericeras corrugatum.
Keywords: ammonites, Grandidiericeras, Santonian, Campanian, Cretaceous, KwaZulu-Natal, South Africa.
The puzosiine genus Grandidiericeras, with Grandidiericeras grandidierorum as type species, was introduced by Collignon in 1961 (pp. 17, 47, pl. 17, fig. 1), [erroneously dated 1960 on p. 47] based on two individuals. The holotype, no. 3915 in the Collections of the Muséum National d'Histoire Naturelle, Paris, has a maximum preserved diameter of 160 mm approximately, and is illustrated here as Fig. 3A-B. Collignon's second specimen, MNHP 3914, was not figured, but the diameter was given as 134 mm. They are from Collignon's locality 157, Ankilizato (Belo sur Tsiribihina), Madagascar, and referred by him to the 'Campanien moyen á Eupachydiscus levyi et Delawarella subdelawarensis.' In 1970, Collignon illustrated a fragmentary specimen (p. 19, pl. 614, fig. 2297), consisting of a nucleus and a 120° sector of phragmocone with a maximum preserved whorl height of 45 mm. It is figured here as Fig. 2B. This specimen came from locality 156 of his Ankilizato (Belo sur Tsiribihina) section, and was referred to his Campanien moyen, 'Zone á Subdelawarella subdelawarensis et Australiella australis' (it should be noted that subdelawarensis is referred to Delawarella elsewhere in Collignon's works, and that Subdelawarella is a nomen nudum). The associated fauna from this locality and zone given in Collignon (1970) indicate an equivalence, in KwaZulu-Natal, to Campanian II of Kennedy & Klinger (1975).
Matsumoto & Saito (1987, p. 1, figs 1-4) described three specimens (and mention several other large individuals left in the field) of a second species, Grandidiericeras nagaoi from the Coniacian of Japan, the largest of which reaches a diameter of at least 500 mm (Matsumoto & Saito 1987, fig. 2). The present specimen, from the Upper Santonian to Lower Campanian of Lake St Lucia in northern KwaZulu-Natal provides a stratigraphic link between these Coniacian and Middle Campanian species.
Suborder AMMONITINA Hyatt, 1889
Superfamily DESMOCERATOIDEA Zittel, 1895
Family DESMOCERATIDAE Zittel, 1895
Subfamily PUZOSIINAE Spath, 1922
Genus Grandidiericeras Collignon, 1961
Grandidiericeras grandidierorum Collignon, 1961, p. 47, pl. 17, fig. 1, from the Middle Campanian of Collignon's locality 157, Ankilizato (Belo sur Tsiribihina), Madagascar.
Grandidiericeras corrugatum sp. nov.
Derivation of name
corrugatus (Latin): wrinkled, referring to the ventral ornament.
The holotype is SAM-PCZ022402 from the Upper Santonian to Lower Campanian St Lucia Formation at locality 105 of Kennedy & Klinger (1975, p. 296).
A Grandidiericeras with well-developed concave, elongate umbilical bullae.
The holotype (Figs 1A-B, 2A) is a fragmentary internal cast of a phragmocone in sparry calcite with an estimated maximum diameter of 130-140 mm, and a maximum preserved whorl height of50 mm. It retains traces ofcalcite spar-replaced shell. Coiling is relatively involute, the umbilicus comprising an estimated 25% of the diameter, shallow, with a low, convex wall and narrowly rounded umbilical shoulder. The flanks are flattened, subparallel, with rounded ventrolateral shoulders and a very feebly convex venter. The whorl breadth to height ratio is 0.64, the greatest breadth well below mid-flank. Twenty-eight ribs arise at the umbilical seam, sweep back across the umbilical wall, then forwards across the umbilical shoulder, where they strengthen into a sharp, concave umbilical bulla. Each bulla gives rise to a single rib, straight and feebly prorsiradiate on the inner flank, flexed slightly back and feebly convex at mid-flank, straight on the outer flank, broadening, and passing straight across the venter, where they are at their greatest breadth and strength, flattened and ribbon-like, with steep adapical and adapertural faces, and separated by subequal interspaces. Four interspaces on the outer whorl are slightly deepened into incipient constrictions. The poorly exposed suture is deeply incised and puzosiine.
Grandidiericeras corrugatum sp. nov. is distinguished from G. grandidierorum (compare Figs 2A and 2B) by its well-developed umbilical bullae and much coarser ribs, which are reduced to mere striae on the early whorls and on the umbilical shoulder of G. grandidierorum at a diameter equivalent to that of the holotype of G. corrugatum. The figured specimens of Grandidiericeras nagaoi (Matsumoto & Saito 1987, figs 1-4) are much larger, but are immediately distinguished by the lack of bullae, and very weak inner flank ribs, the ribs narrower, finer and more numerous, with more numerous long and short intercalatories on the middle and outer flank.
The St Lucia Formation at locality 105 is exposed in a 2-3 metre cliff and ca. 100 m foreshore exposure that spans the boundary between Santonian III and Campanian I of Kennedy & Klinger (1975); see detailed log in Klinger & Kennedy (1980, fig. 130). The precise level of occurrence of the specimen is not recorded.
We thank the staff of the Department of Earth Sciences, Oxford, the Oxford University Museum of Natural History, and the Natural History Collections Department, Iziko South African Museum, Cape Town, for technical support. Kennedy acknowledges the financial support of the Oppenheimer Fund (Oxford) and Klinger financial support from the NRF (South Africa).
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Received 26 July 2011
Accepted 5 October 2011