Anagaudryceras sp.

Raffi, María E., Olivero, Eduardo B. & Milanese, Florencia N., 2019, The gaudryceratid ammonoids from the Upper Cretaceous of the James Ross Basin, Antarctica, Acta Palaeontologica Polonica 64 (3), pp. 523-542 : 530

Anagaudryceras sp. juvenile 1

Fig. 5C, D .

Material.—11 internal molds preserving patches of the shell and including the phragmocone and part of the body chamber (CADIC PI 533–542, 548). From early Campanian Cretaceous), upper part of the Ammonite Assemblage 2 Natalites rossensis to lower part of Ammonites Assemblage 4 Grossouvrites occultus – Maorites , upper part of the Alpha Member and lower part of the Beta Member, Santa Marta Formation, James Ross Island, Antarctica.

Description. —Evolute coiling and fairly compressed (Wb/ Wh ~0.82–0.94; Table 3) whorl section. Wide umbilicus (U ~35%; Table 3), slightly gradual umbilical wall, and rounded umbilical shoulder. The flanks converge to a well defined ventrolateral shoulder and rounded and slightly arched venter. The shell becoming less evolute as the diameter increases. Early-whorl ornamentation almost imperceptible to the naked eye, but consists of very fine and prorsiradiate lirae accompanied by slightly sinuous constrictions preceded by collars. At the body chamber the ornamentation becomes stronger with several collars and intercalate ribs.

Remarks.—Even though our specimens are small juveniles, their style of ornamentation differ from the other species of Anagaudryceras described herein. Anagaudryceras subtilineatum ( Kossmat, 1895) from the Campanian of India present fine lirae and infrequent weak constrictions preceded by collars but is fairly depressed (Wb/Wh ~1.4) at diameters of 15–45 mm (see Kossmat 1895: 123; Kennedy and Klinger 1979: 156, and Henderson and McNamara 1985: 45).

Figures

Fig. 5. The gaudryceratid ammonoid Anagaudryceras, early Campanian (Upper Cretaceous) of Antarctica, from Rabot Formation, Redonda Point locality (A, B) and from Santa Marta Formation, Brandy Bay locality (C, D). A, B. Anagaudryceras cf. A. politissimum (Kossmat, 1895). A. CADIC PI 455. B. CADIC PI 454. C, D. Anagaudryceras sp. juvenile 1. C. CADIC PI 533. D. CADIC PI 534. In lateral (A1–D1) and ventral (A2–D2) views. Arrows mark the beginning of the body chamber.