Gattendorfia corpulenta Korn & Weyer 2023, sp. nov.

Gattendorfia corpulenta sp. nov. urn:lsid:zoobank.org:act: 95790C3B-9B58-492E-BFD6-2D1CC0154C0C Figs 77–78; Tables 75–76 Gattendorfia crassa – Schindewolf 1952: 296, pl. 2 fig. 5, text-figs 16–17. Gattendorfia costata – Vöhringer 1960: 152, text-figs 27, 37. — Dzik: 107, text-fig. 28f. — Weyer 1977: 173, pl. 1 figs 1, 7. — Korn 1994: 73, text-figs 66d, 67a. — Korn & Weyer 2003: 100, text-fig. 14h–i. Diagnosis Species of Gattendorfia with a conch reaching 70 mm diameter. Conch at 5 mm dm thickly discoidal, evolute (ww/dm ~0.58; uw/dm ~0.50); at 15 mm dm thinly pachyconic, subevolute (ww/dm ~0.70; uw/ dm ~0.40); at 40 mm dm thickly pachyconic, subinvolute (ww/dm ~0.75; uw/dm ~0.25). Whorl profile in the juvenile stage crescent-shaped, at 40 mm dm moderately depressed (ww/wh ~1.65); coiling rate moderately high (WER ~1.85). Venter broadly rounded throughout ontogeny, umbilical margin narrowly rounded in the adult stage. Growth lines fine, wide-standing, with convex course. Weak constrictions on the shell surface and weak internal shell thickenings; sharp, short ribs on the inner flank. Suture line with lanceolate external lobe and V-shaped adventive lobe. Etymology From the Latin ‘ corpulenta ’, referring to the stout conch. Material examined Holotype GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; illustrated in Fig. 77A; MB.C.31160.1. Paratypes GERMANY • 1specimen; RhenishMountains, Oberrödinghausen,railwaycutting; HangenbergLimestone, bed 3a; Vöhringer Coll.; GPIT-PV-63950 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; GPIT-PV-63896, GPIT-PV-63936 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3b; Vöhringer Coll.; MB.C.31159 • 3 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; MB.C.31160.1–3 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Vöhringer Coll.; MB.C.31161 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, loose material; Vöhringer Coll.; MB.C.31162 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Korn 1982 Coll.; MB.C.31163 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Weyer 1993–1994 Coll.; MB.C.31164 • 1 specimen; Rhenish Mountains, Hasselbachtal; Hangenberg Limestone, bed 76; Weyer 1993–1994 Coll.; MB.C.5247.4. Description Holotype MB.C.31160.1 is a specimen, which had been sectioned already by Vöhringer, but it has no internal whorls preserved. The specimen has a diameter of 44 mm and is thickly pachyconic and subinvolute (ww/dm = 0.74; uw/dm = 0.24) with a narrowly rounded umbilical margin, a convex umbilical wall and broadly rounded flanks and venter (Fig. 77A). There are fine, sharp ribs on the umbilical margin, spaced 1.5 to 2 mm apart, which extend over a distance of about 8 mm on the flanks. The ribs are directed slightly backwards. A faint constriction is visible, also directed backwards, forming a broad, shallow sinus across the venter. Paratype MB.C.31164 is a fragment of a specimen of 40 mm conch diameter (Fig. 77B). The conch morphology can only be partially reconstructed, but it apparently differs only slightly from the holotype. Remains of the shell on the inner half of the flank are preserved, showing lamellar growth lines with a backward course. An internal shell thickening also has a posteriorly directed course. Paratype GPIT-PV-63896 is a sectioned specimen with 27.7 mm diameter of the conch; it allows the study of five whorls (Fig. 78B). The section shows that the conch becomes continuously stouter in the interval between 5 and 27 mm diameter (ww/dm increases from ~0.50 to ~0.85). The whorl profile is very similar in all whorls, only the last half whorl shows a more pronounced subangular umbilical margin. The suture line of this paratype has a lanceolate external lobe with weakly divergent flanks, an inverted U-shaped ventrolateral saddle and an asymmetric adventive lobe with steep ventral and sigmoidally curved dorsal flank (Fig. 78D). Paratype MB.C.31162 is another sectioned specimen showing the morphological development of the conch geometry of all whorls up to a diameter of 15 mm (Fig. 78C). It complements paratype GPIT- PV-63896; it is remarkable that the whorl profile shows almost no ontogenetic changes. The diagrams of the ontogenetic trajectories show an inconsistent picture with respect to the cardinal conch parameters (Fig. 78 E-G). The ww/dm trajectory is triphasic, with the first phase describing a decrease in the ww/dm ratio from about 0.90 at 1 mm dm to a minimum of ~0.47 at 5 mm dm; the second phase describing an increase to ~0.85 at 27.7 mm dm. The third phase with reduction of the ww/ dm ratio is only visible in specimens over 30 mm in diameter. The uw/dm curve is biphasic and runs diametrically to the ww/dm curve. It shows the highest value of ~0.58 at a diameter of 5 mm. In contrast, the ww/wh trajectory does hardly change between 1 and 27 mm conch diameter and ranges between 1.85 and 2.25. Only with larger specimens over 40 mm diameter does the value decrease to 1.50–1.75. The WER trajectory is monophasic and shows a slow increase from 1.50 at 2 mm diameter to 1.67 at 27 mm dm. Remarks Gattendorfia corpulenta sp. nov. differs from most species of the genus by its stout conch form. Gattendorfia corpulenta differs in the narrower umbilicus from G. costata; at 30 mm dm, the uw/dm ratio is ~ 0.30 in G. corpulenta, but ~ 0.45 in G. costata. A superficially rather similar species is Z. oblita sp. nov., but this has constrictions that are clearly concavo-convex in their course. Superficially, Zadelsdorfia crassa is also similar, but at a conch diameter of 30 mm more slender (ww/ dm ~0.65) than G. corpulenta (ww/dm ~0.80); Z. crassa does not possess ribs and has a pouched external lobe.Published as part of Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), pp. 1-230 in European Journal of Taxonomy 882 on pages 131-134, DOI: 10.5852/ejt.2023.882.2177, http://zenodo.org/record/817758