Pseudaganides Spath, 1927

Branger, Patrick, 2024, Antaganides n. gen., a new genus of Middle Jurassic nautiloid, ancestor of Pseudaganides Spath, 1927, with discussion on the phyletic origin of the family Pseudonautilidae, Geodiversitas 46 (14), pp. 471-493 : 480-482

Genus Pseudaganides Spath, 1927

Pseudaganides Spath, 1927: 22-25 .

TYPE SPECIES. — Nautilus kutchensis Waagen, 1873 , by original designation, from the Callovian of Kutch, India.

COMPOSITION OF THE GENUS. — Six nominal species are assigned to this new genus within Bathonian and Callovian, Pseudaganides aquitanense n. sp. from Upper Bathonian, Retrocostatum Zone, Pseudaganides buffeventi n. sp., Lower Callovian, Bullatus Zone, Pseudaganides crechensis n. sp., Lower Callovian, Gracilis Zone, Prahecquense Subzone , Pseudaganides subbiangulatus and Pseudaganides dimidiatus Marchand & Tintant, 1971 , from the Lower to Middle Callovian, Patina Subzone, Boginense Horizon to the Anceps Zone, Bannense Subzone and Pseudaganides aganiticus (Schlotheim, 1820) , Upper Callovian to Lower Oxfordian. Many other Pseudaganides from the Upper Jurassic (von Loesch 1914) have also to be included within the genus, a revision of this material would be necessary. Based on the angular shape of the ventral lobe, Shimansky & Erlanger (1955) distinguished the genus Xenocheilus Shimansky, 1957 that extends from Upper Oxfordian to Lower Cretaceous beds.

CHARACTERIZATION AND REMARKS

Genus Pseudaganides is a group including small to Middle sized nautiloids, less than 15 centimeters in diameter, mostly around 10 centimeters or less. Shells are compressed, bearing goniatitic suture lines at all growth stages. These suture lines are characterized by a deep lateral lobe, a dorsal saddle on the entire phragmocone and a ventro-lateral saddle. The ventral lobe is sometimes missing. In most stages of coiling the umbilicus is closed. On the inner whorls, the venter is rounded and flattens, sometimes slightly concave, on the body-chamber. As pointed out by Jeannet (1948: fig. 4) for P. frickensis , the opening of the shell is rather particular, lateral borders are quite straight, starting from the umbilicus with a spiny shaped beginning ( Figs 13D 1 ; 15C). A deep ventral sinus is always present. The siphuncle is typically close to the venter part of the shell. Pseudaganides is known from the top of the Bathonian to the end of the Jurassic from which many new species were described (von Loesch 1914). P. portlandicus ( Foord & Crick 1890) is atypical, showing an oval and larger shell. It could belong to another genus. All the specimens from the Lower Jurassic to Lower Middle Jurassic with folded suture lines are now gathered within the genus Belmonticeras Rulleau, 2008 . From a palaeogeographical point of view, Pseudaganides seems to be a typical faunal element from the Tethyan realm sensu Westerman (2000) and has not yet been reported from the Arabian realm ( Tintant 1987). Due to the ventral position of the siphuncle and the strong folding of the septum sutures, it is generally accepted that species of the genus Pseudaganides were cephalopods adapted to moderately deepwater environments ( Tintant 1987).

Figures

FIG. 13. — A, Antaganides cf. erycinus (Tagliarini, 1901), n. comb., specimen 2023.PB.N129, with its preserved muscle scar, Niort, Upper Bajocian, Niortense Zone; B, Antaganides cf.erycinus (Tagliarini,1901),n.comb.,specimen 2023.PB.N148, with its siphuncle,viaduc de l’Égray,Upper Bajocian,Niortense Zone;C, Pseudaganides crechensis n. sp.,specimen 2023.PB.N143, newly hatched shell showing its reticulate ornamentation on the phragmocon;D1-D3, Pseudaganides subbiangulatus (d’Orbigny,1850),specimen 2023.PB.N110, full grown shell with itswell preserved aperture,Bougon,Lower Callovian,Gracilis Zone,Patina Subzone,Boginense Horizon; E1-E3, Pseudaganides subbiangulatus, specimen 2023.PB.N112, Niort,Middle Callovian,Anceps Zone,Stuebeli Subzone.*, end of the phragmocone.Scale bars:1 cm.

FIG. 1. — Geographical map reporting the position of the localities that provided specimens of Antaganides n. gen.and Pseudaganides Spath,1927: 1, Buffevent quarry;2, Niort; 3, Aiffres; 4, Trotte-buie quarry; 5, A83 highway trench at Viaduc de l’Égray; 6, Les Lucs (Échiré); 7, Chaban-de-Chauray; 8, La Crèche; 9, Salles; 10, Bougon; 11, Les Hauts-de-Rochefort quarry; 12, Les Maisons-Blanches; 13, La Grève quarry near Saint-Laon; 14, Montreuil-Bellay.