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 Author Branger, Patrick 4 rue Franche F- 79410 Cherveux (France) patrick.branger@wanadoo.fr text Geodiversitas 2024 2024-10-03 46 14 471 493 https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/g2024v46a14.pdf journal article 304151 10.5252/geodiversitas2024v46a14 a6dcf4e3-2ba8-4c57-a797-1e57727505c5 1638-9395 13884433 urn:lsid:zoobank.org:pub:2C97C1BD-2DAA-485A-8AE0-2E3DD501D5F2 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”. TABLE 1. — Measurements (D,H, W,U, P,L, in mm) for Antaganides cf. erycinus ( Tagliarini, 1901 ) , n. comb.

n°	D	H	h	W	w	U	u	W/H	P	L	%
2023.PB.N117	54	33	0.6	29	0.53	0	0	0.87	3	18	16
34	19	0.55	16	0.47	0	0	0.84	–	–	–
2023.PB.N129	52	32	0.61	31	0.59	0	0	0.96	4	15	20
39	25	0.66	20	0.51	0	0	0.8	–	–	–

FIG . 2. — Dimensional characteristics measured in this study, drawing from Dzik (1984) . 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 ).