Acanthoceras Neumayr, 1875

Barroso-Barcenilla, Fernando, Antunes, Miguel Telles, Brandão, José Manuel, Callapez, Pedro Miguel, Santos, Vanda Faria dos & Segura, Manuel, 2018, The d’Orbigny Palaeontological Collection of the National Museum of Natural History and Science, Lisbon, Portugal: Historical perspective and revision of Cretaceous Cephalopoda, Geodiversitas 40 (20), pp. 505-519 : 512

Genus Acanthoceras Neumayr, 1875

Acanthoceras rhotomagense ( Brongniart, 1822) ( Fig. 3 H-J)

MATERIAL. — Six phosphatised internal moulds, one of them with a glued indication (463). Original label: Nº 463/ Ammonites rhotomagensis (Lamarck), Andar 20º Cenomaniense, Terreno Cretaceo, Localidade Rouen (Seine inf. re). See Figs 1D; 3K.

DESCRIPTION

Relatively large-sized, evolute and ornamented ammonites with subpoligonal whorl section.Tabular venter, conspicuous ventrolateral margins, arched flanks and wide umbilici with bended walls. Ornamentation formed by 24-28 straight ribs per whorl, with umbilical, inner ventrolateral, outer ventrolateral and siphonal tubercles. During ontogeny, whorl section changes from depressed subrounded to compressed subpolygonal. Relatively simple acanthoceratid suture lines.

DISCUSSION

Already cited in the Sainte-Catherine Mountain of Rouen by d’Orbigny (1840: 348), as characteristic of “des craies chloritées, des craies tufau [sic], ou des grès verts supérieurs” of France. This morphologically highly variable middle Cenomanian species, type of the genus, was attributed to Lamarck by some authors, such as d’Orbigny (1850, p. 146). Wright & Kennedy (1987) included within its synonymy numerous taxa proposed by different authors, as detailed by Barroso-Barcenilla (2004). Among the morphologically closest forms of the genus, the stratigraphically overlaying species A. jukesbrownei ( Spath, 1926) has less numerous and more distant ribs with strong umbilical bullae, and weak inner ventrolateral tubercles that decline to give a characteristic trapezoidal (rather than polygonal) whorl section. In the last years, A. rhotomagense has been studied by some authors, such as Kennedy & Juignet (1993), Kaplan et al. (1998), Fischer & Gauthier (2006) andKennedy et al. (2011).

Family COILOPOCERATIDAE Hyatt, 1903

Figures

FIG. 3. — Cretaceous ammonites of the d’Orbigny Collection of the National Museum of Natural History and Science (Museu Nacional de História Natural e da Ciência): A-D, Neolissoceras grasianum (d’Orbigny, 1840) in ventral (A), lateral (B) and oral (C) views, and original label (D): Nº 357/Ammonites grasanus (d’Orb), Andar 17º Neocomiense, Terreno Cretaceo, Localidade S.t Julien (Hautes Alpes); E-G, Pleurohoplites (Pleurohoplites) renauxianus (d’Orbigny, 1840) in lateral (E) and ventral (F) views, and original label (G): Nº 464/Ammonites Renauxianus (d’Orb), Andar 20º Cenomaniense, Terreno Cretaceo, Localidade Mont-Blainville (Meuse); H-K, Acanthoceras rhotomagense (Brongniart, 1822) in oral (H), lateral (I) and ventral (J) views, and original label (K): Nº 463/Ammonites rhotomagensis (Lamarck), Andar 20º Cenomaniense, Terreno Cretaceo, Localidade Rouen (Seine inf.re). Scale bar: 2 cm.