Antaganides, Branger, 2024

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 : 473-474

Genus Antaganides n. gen.

urn:lsid:zoobank.org:act:38E29292-9BB1-487E-9D3D-A60892F08633

DIAGNOSIS. — Small sized shells, maximum around 60 mm or less at adult stage, compressed, showing a wide shallow lateral lobe and a shallow ventral lobe. Septa moderately spaced, 8 to 9 chambers are present for half a whorl. Flanks slightly rounded and venter flattens on the body-chamber. Most species posess a closed umbilicus except as juveniles.When visible, the siphuncle is close to the venter.

TYPE SPECIES. — Antaganides fournieri n. sp. (Fig. 3C1-C3).

COMPOSITION OF THE GENUS. — Four nominal species are assigned to this new genus, Antaganides cf. erycinus ( Tagliarini, 1901) , n. comb. from the Upper Bajocian, Niortense Zone, Antaganides sauvageti n. gen., n. sp. from the Lower Bathonian, Zigzag Zone, Antaganides fournieri n. gen., n. sp. from the Middle Bathonian, Progracilis and Bremeri Zones and Antaganides grulkei n. gen., n. sp. from the same level. None of the new species described here has previously been reported or figured by any author.

ETYMOLOGY. — Genus Aganides , the first name given by Spath to the group of Nautilus kutchensis Waagen, 1873 , later transformed into Pseudaganides due to preoccupation of the name, combined with the prefix “ante” meaning “before”.

OCCURRENCE. — To date, Antaganides n. gen. has been recorded from Upper Bajocian and Bathonian.

REMARKS

Due to its small relative size and compressed shell shape, Antaganides n. gen. cannot be mistaken with any other contemporaneous Middle Jurassic nautilids. From the Inferior Oolite Formation, Crick (1898) described two small sized species, Cenoceras fuscum ( Crick, 1898) and Cenoceras bradfordensis ( Crick, 1898) . These species are also reported from the Upper Bajocian ( Chirat 1997). Cenoceras fuscum differs by its more robust section, its well-marked angular margins, and a different aperture (see Chirat 1997: pl. 5, figs 4-5) and the umbilicus is more open. Pictonautilus Branger, 2004 of Bathonian age has the same characteristics. Cenoceras bradfordensis is closer to Antaganides n. gen., a little larger and a little older. For this species, Crick (1898) recognized two morphospecies, one with a compressed shell and another with a more inflated section. He considered this difference to be due to sexual dimorphism. Cenoceras bradfordensis could be an ancestor of Antaganides n. gen. but further studies will clarify if this species should be integrated into the new genus. The closest genus to Antaganides n. gen. is represented by Pseudaganides , with many morphological similarities: h, w, u, W/H ( Figs 5-8 ). The ratio “h” of the height of the whorl compared with the diameter of the shell (H/D) among the different species of Antaganides n. gen. and Pseudaganides is about 0.6, and is fairly constant ( Fig. 5 ). The ratio “w” of the width of the whorl compared with the diameter of the shell (W/D) varies from 0.4 to 0.6 within the two genera ( Fig. 6 ). The umbilical width compared with the diameter of the shell (U/D = “u”) is always very low, from 0 to 0.1 except for one Pseudaganides species ( Fig. 7 ). The individuals of both genera are relatively compressed, W/H varies between 0.7 and 1, sometimes a little less ( Fig. 8 ). The main difference consists in the shape of the septal suture lines which is particularly folded on the whole shell of Pseudaganides ( Figs 4 ; 9 ).

Figures

FIG. 5. — Ratio “h” of the height of the whorl compared with the diameter of the shell (H/D) among the different species of Antaganides n. gen. and Pseudaganides Spath, 1927.

FIG. 6. — Ratio “w” of the width of the whorl compared with the diameter of the shell (W/D) among the different species of Antaganides n. gen. and Pseudaganides Spath, 1927.

FIG. 7. — Ratio “u” of the umbilical width compared with the diameter of the shell (U/D) among the different species of Antaganides n. gen. and Pseudaganides Spath, 1927.

FIG. 8. — Ratio “W/H” of the shell among the different species of Antaganides n. gen. and Pseudaganides Spath, 1927.

FIG. 4. — Suture lines of Antaganides n. gen. and Pseudaganides Spath, 1927: A, Antaganides cf. erycinus (Tagliarini,1901), n. comb., 2023.PB.N117; B, Antaganides sauvageti n. gen., n. sp. 2023.PB.N64; C, Antaganides fournieri n. gen., n. sp., 2023.PB.N105; D, Pseudaganides aquitanense n. sp., 2023.PB.N96; E, Pseudaganides buffeventin. sp.,2023.PB.N76; F, Pseudaganides crechensisn. sp., 2023.PB.N107; G, Pseudaganides subbiangulatus (d’Orbigny,1850),2023. PB.N73, Patina Zone; H, Pseudaganides subbiangulatus, 2023.PB.N112, Anceps Zone.

FIG. 9. — Ratio “P/L” of the depth of the width of the lateral lobe compared with its width among the different species of Antaganides n. gen. and Pseudaganides Spath, 1927.