Pseudaganides subbiangulatus (d’Orbigny, 1850)

(Figs 13D, E; 14A; 15A1-A3)

Nautilus subbiangulatus d’Orbigny, 1850: 296, n°2.

Nautilus biangulatus d’Orbigny, 1842: 160, pl.134, fig. 1-3.

? Nautilus textilis Hébert & Eudes-Deslongchamps, 1860: 5, pl. I, fig. 1a-c.

Pseudaganides subbiangulatus – Marchand & Tintant 1971: 146, pl. IV, 1a, b. — Tintant 1994: 35, pl. 8, fig. 5.

Pseudaganides cf. aganaticus – Rulleau 2008: 55, pl. 35, fig. 2a, b.

non Pseudaganides subbiangulatus – Courville 2013: 66, pl. 1, fig. 2a, 2b (synonym of Cenoceras sp. or Paracenoceras sp.)

DIAGNOSIS. — Large sized nautilus for the genus, compressed subrectangular section with a flattened venter, becoming concave and boarded by angular margins on the body-chamber. Suture line with a deep lateral lobe followed by a wide lateral saddle.

MATERIAL EXAMINED. — France • 1 specimen (near complete); Nouvelle-Aquitaine, Pamproux (POC 0015); [46°23’43”N, 0°3’0”W]; Patina Zone; Patrick Branger leg.; MBAN; 2023.PB.N73 • 1 specimen (near complete); Nouvelle-Aquitaine, Limalonges, les Maisons-Blanches; [46°08’15”N, 0°10’28”E]; Zone?; Age?; Patrick Branger leg.; MBAN; 2023.PB.N74 • 1 specimen (near complete); Nouvelle-Aquitaine, Bougon; [46°21’18”N, 0°03’11”W]; Gracilis Zone, Patina Subzone, Boginense Horizon; Lower Callovian; Patrick Branger leg.; MBAN; 2023.PB.N110 (Fig. 13D 1-D 3) • 1 specimen (near complete); Nouvelle-Aquitaine, Niort; [46°18’25”N, 0°27’42”W]; Anceps Zone, Stuebeli Subzone; Middle Callovian; Patrick Branger leg.; MBAN; 2023.PB.N112 (Fig. 13E 1-E 3) • 1 specimen (near complete); Nouvelle-Aquitaine, Saint-Laon, la Grève quarry (POC 0051); [46°57’19”N, 0°01’38”W]; Anceps Zone; Middle Callovian; Patrick Branger leg.; MBAN; 2023.PB.N144 (Fig. 14A1- A3) • 1 specimen (near complete); Nouvelle-Aquitaine, Chauray, Chaban; [46°21’08”N, 0°17’58”W]; Patrick Branger leg.; MBAN; 2023.PB.N149; • 1 specimen (near complete); Nouvelle-Aquitaine, La Crèche; [46°21’08”N, 0°17’58”W]; Gracilis Zone; Lower Callovian; Patrick Branger leg.; MBAN; 2023.PB.N155 (Fig. 15A1-A3).

MEASUREMENTS. — See Table 8.

DESCRIPTION

The lectotype (MNHN.F.R54480, d’Orbigny collection n°2593 B, stored at the Muséum national d’Histoire naturelle, in Paris) has been revised by Marchand & Tintant (1971: 142, pl. IV, 1a, b). It consists in a large sized specimen (136 mm) for the genus Pseudaganides, well preserved, just a little distorted. The body-chamber is not complete. The umbilicus is rather narrow (Fig. 7) with an oblique umbilical wall. Its section is higher than wide, flanks are rounded with a maximum width at about one third of the height. The upper part of the flanks is slightly depressed at the end of the phragmocone and it is separated from the venter by a smooth but well-marked ridge. The flanks of the body-chamber are more rounded. The ventral area is narrow, convex on the phragmocone, slightly concave on the body-chamber. Suture line (Fig. 4G, H) is very sinuous with a wide and deep lateral lobe (P/L = 0.55) and a shallow ventral lobe.

Among our seven specimens, six are a little smaller than the lectotype (measurements from Marchand & Tintant, 1971), the maximum diameter observed is 111 mm, but their shape and septa fit perfectly with the diagnosis of P. subbiangulatus . The sample from the collection of the École des Mines figured by Rulleau (2008) also belong to the same species. Only one specimen, 2023.PB.N155 (Fig. 15A1-A3), although distorted, is as large as the lectotype.

REMARKS

Pseudaganides subbiangulatus is the largest Pseudaganides species (Fig. 10). When Marchand &Tintant (1971) wrote their revision, they considered that among d’Orbigny’s material only one specimen was fitting perfectly to the type. Following his stratigraphical placement, they restricted the species to large specimens of Upper Bathonian age. The samples clearly show that all these former stratigraphic attributions are probably erroneous. Some smaller, below 80 mm, but very similar Pseudaganides of Lower and Middle Callovian age were described by Marchand & Tintant (1971: pl. II, fig. 1a-b-c, fig. III, pl. 6) as a new subspecies, Pseudaganides subbiangulatus subsp. dimidiatuo, later named Pseudaganides dimidiatus (Tintant 1994) . The average size of this new species from Western France and Spain was much smaller than Pseudaganides subbiangulatus and is also very different from our specimens, see below.

According to our data and the patterns of the evolution of the genus Pseudaganides (see Origin and evolution of the Antaganides-Pseudaganides group) we assume that the initial stratigraphic placement to the Upper Bathonian by A. d’Orbigny (1842) was erroneous. This fossil was collected by Mr. Cabannet in the neighbourhood of Nantua (French Jura) but, more probably, the lectotype should have been collected within the “alternance calcaréo-marneuse” from the Lower or Middle Callovian described in Nantua’s area by Mangold & Énay (2004). Pseudaganides subbiangulatus (d’Orbigny, 1850) is now considered as a nautilus of Lower and Middle Callovian age, from the Gracilis Zone, Grossouvrei or Pictava Subzone, to the Anceps Zone, Bannense Subzone.