Pseudaganides aganiticus (Schlotheim, 1820)

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 : 487

Pseudaganides aganiticus (Schlotheim, 1820)

(Fig. 14C1-C3)

Nautilites aganiticus Schlotheim, 1820: 63 . — von Loesch 1914: pl. XV (VI), fig. 1a-b.

Pseudaganides aganiticus – Marchand & Tintant 1971: 146, pl. IV, fig. 1a-b. — Jain et al. 2023: 17, fig. 14A-H.

DIAGNOSIS. — Small shells, maximum diameter about 90 mm. The umbilicus is quite small, the section is higher than wide with flat sides converging toward a narrow and rounded venter on the phragmocone. This venter flattens on the body-chamber, becoming rarely concave. Most of the time it is boarded by angular ventrolateral shoulders. Suture line with a wide and deep dissymmetric lateral lobe, lateral saddle narrow and quite short, shallow, and rounded ventral lobe.

MATERIAL EXAMINED. — France • 1 specimen (complete); Pays de la Loire, Montreuil-Bellay; [47°06’37”N, 0°06’14”W]; top of the Anceps Zone ; Middle Callovian; Patrick Branger leg.; MBAN; 2023.PB.N111 (Fig. 14C1-C3) .

MEASUREMENTS. — See Table 10.

DISTRIBUTION. — The oldest sample that can be attributed to this taxon has been taken from the top of the Anceps Zone, Middle Callovian. It is a common species within Upper Callovian and Lower Oxfordian ( Marchand & Tintant 1971; Jain et al. 2023).

DESCRIPTION AND REMARKS

As the investigations were mainly focused on Jurassic strata from southern Deux-Sèvres, the collection is lacking in Upper Callovian examples. Nevertheless, the few Pseudaganides from these beds clearly belong to P. aganiticus (Schlotheim) . This species has been revised by Marchand & Tintant (1971) and no further comment is needed. It differs from P. subbiangulatus in three major points, a more rounded section on the flanks, a smaller size ( Fig. 10 ) and a rather closed umbilicus ( Fig. 7 ).

Figures

FIG. 10. — Evolution of the size of the adult shell and phragmocone among the different species of Antaganides n. gen. and Pseudaganides Spath, 1927 for full grown shells.

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.