Bournonia excavata d'Orbigny, 1842

Săsăran, Liana, Săsăran, Emanoil & Bucur, Ioan I., 2018, Upper Cretaceous Rudist-Bearing Mixed Siliciclastic-Carbonate And - Volcanoclastic Deposits From Strâmturii Valley, Borod Basin, Northern Apuseni Mountains: Description, Microfacies And Depositional Environments, Acta Palaeontologica Romaniae 14 (1), pp. 3-20 : 9

Bournonia excavata d'Orbigny, 1842

Fig. 7 a-b

1842 Radiolites excavata - d’Orbigny, p. 156, 185.

1850 Radiolites excavata d’Orbigny- p. 215, pl. 556.

1907 Bournonia excavata (d’Orbigny) - Toucas, p. 27, pl. 2, figs. 11-13a.

1912 Bournonia excavata (d’Orbigny) - Parona, p. 285, fig. 4.

1968 Bournonia excavata (d’Orbigny) - Pejović, pl. 5, fig. 2.

1989 Bournonia excavata (d’Orbigny) - Cestari and Sirna, p.145, fig.3.

1992 Bournonia excavata (d’Orbigny) - Vicens, p. 185, pl. 74, fig. 1.

1995 Bournonia excavata (d’Orbigny) - Caffau and Pleničar, p. 230; pl. 7, figs. 2, 2a; pl. 12, fig.3.

1995 Bournonia excavata (d’Orbigny) - Cestari and Sartorio, p.136.

1995 Bournonia excavata (d’Orbigny) - Scott, p. 303, pl.2, figs. 3-4; text-fig. 6-D.

1999 Bournonia excavata (d’Orbigny) - Sirna & Paris, p.51, pl. X, fig. 3.

2002 Bournonia excavata (d’Orbigny) - Caffau, p. 92-94, figs.2-3.

2005 Bournonia excavata (d’Orbigny) - Pleničar, p. 80, pl.28 figs. 1-2.

2007 Bournonia excavata (d’Orbigny) - Macé-Bordy, p. 99-100, fig. 9D-E.

2008 Bournonia excavata (d’Orbigny) - Pons and Vicens, p. 230, fig. 14C.

Material: one RV (24078-BBU-MPS).

Description: Lower attached RV is conical, height up to 55 mm (incomplete) ( Fig. 7 a-b). The ornamentation of the shell as well as the outer shell layer from the anterior side of RV is entirely removed probably due to erosion. In ventral side only Pb is visible as a prominent costa that corresponds to downfolds of the laminae of the outer shell layer. Vb is broken but its location can be easily recognized. Vb and Pb are separated by a narrow furrow, 9 mm wide, concav (Ib). In the transverse section, the contour of the RV is oval to quadrangular, with a flat posteroventral side, having a diameter of about 30 mm antero-posterior and 40 mm dorsal-ventral ( Fig. 7a ). The elements of the myocardinal apparatus are visible (pm) and (am) and the (at) and (pt) ( Fig. 7a ); the ligamental ridge is absent. Transverse sections of the RV indicate two well defined layers. The inner layer is less 1 mm thick and is represented by calcite spar. The thickness of the outer shell layer varies from 3-4 mm in dorsal and posterior side to 10 mm in area of Pb. The outer shell layer has a prismatic structure, typical for the Bournonia genus.

Remarks: Specimens very similar with Bournonia excavata d’Orbigny have been reported by Douvillé (1910, 1913, 1915) and recently by Abdel-Gawad et al. (2011) from Turonian deposits in Egypt. This fact has a great implication extending to Turonian stratigraphical ranges of species B. excavata Also , detailed taxonomical studies on small shelled species of B. fourtaui and B. africana are required, because of their morphological similarities with B. excavata ( Steuber, 1999) . If these three species formed a single species ( Steuber, 1999) thus Bournonia excavata (d’Orbigny, 1850) has priority according to the rules of International Commission on Zoological Nomenclature (ICZN, Ride et al., 1999).

Age: middle Santonian in Spain ( Vicens et al, 1998; Pons and Vicens, 2008) and France ( Toucas, 1907); late Santonian–early Campanian in Croatia (Polšac and Mamuzic, 1969), Italy ( Sirna and Paris, 1999), Romania ( Lupu, 1976), Slovenia ( Pleničar, 2005); late CampanianMaastrichtian in southern Italy ( Cestari and Sirna, 1989) and Guatemala - Carribean Province ( Scott, 1995); Maastrichtian in Montenegro ( Pejović, 1968)

Figures

Fig. 7 a, b Bournonia excavata d'Orbigny, 1847, (inventory no. 24078 BBU-MPS =no.1246 sample field); a transverse section through RV close to the commissure, showing the myocardinal elements: anterior and posterior tooth and myophores (am, pm) of the opposite valve; b view of flat posteroventral side of RV; c Gorjanovicia endrissi (Böhm)(24079 BBU-MPS) – transverse section of RV showing compact layer, concave ventral band (Vb); Ib- narrow and wide Pb with 3 fine rounded costae; d, e Praeradiolites subtoucasi (Toucas): d transverse section through RV (24080-BBU-MPS), unknown commissure. The outer shell layer from ventral side is eroded thus the radial bands are missing. e transverse section on other specimen (24081-BBU- MPS) having outer shell layer partially broken but preserve the myocardinal apparatus. f, g Radiolites squamosus (d'Orbigny): f specimen with both valves showing convex LV, very eroded and the ornamentations of RV consist in dense growth lamellae (sample no. 24082 BBU-MPS); g ventral side of RV of the same specimen showing radial bands (Vb and Pb) with folds upward to commissure and the narrow interband (Ib). h-i Radiolites nouleti (Bayle)(sample no. 24083 BBU-MPS): h large conical RV, thick-shelled, with dense folded growth lamellae, slightly ondulated in large interband (Ib); i transverse section in RVof the same specimen, showing thick cellular outer shell layer, ligamental ridge and accessory cavities. j, k Sphaerulites boreaui (Toucas)(sample no. 24084 BBU-MPS), j specimen with both valves, top view, showing LV, thin and smaller than lower valve and large RV with expanded, sub-horizontal growth lamellae; k transverse section through RV, showing thickness of cellular