Gattendorfia bella, Korn & Weyer, 2023

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), European Journal of Taxonomy 882, pp. 1-230 : 120-122

Gattendorfia bella sp. nov.

urn:lsid:zoobank.org:act:4E3879AA-60BF-456A-938F-F71F8700C9B9

Figs 70–71 ; Tables 68–69

Gattendorfia tenuis – Vöhringer 1960: 153, text-fig. 29. — Korn 1994: 75, text-figs 66f, h.

Diagnosis

Species of Gattendorfia with a conch reaching 60 mm diameter. Conch at 5 mm dm thinly discoidal, evolute (ww/dm ~0.40; uw/dm ~0.55); at 15 mm dm thinly discoidal, evolute (ww/dm ~0.40; uw/dm ~0.50); at 40 mm dm thinly discoidal, evolute (ww/dm ~0.40; uw/dm ~0.50). Whorl profile in the juvenile stage depressed oval, at 40 mm dm weakly depressed (ww/wh ~1.35); coiling rate low (WER ~1.75). Venter broadly rounded throughout ontogeny, umbilical margin broadly rounded throughout ontogeny. Growth lines lamellar, wide-standing, with convex course. Deep constrictions on the shell surface and prominent internal shell thickenings.

Etymology

From the Latin ‘ bella ’ = ‘pretty’; referring to the regular conch shape and ornament.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3e; Weyer 1993–1994 Coll.; illustrated in Fig. 70A ; MB.C.31151.1.

Paratypes

GERMANY • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; GPIT-PV-63942 • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 5; Vöhringer Coll.; GPIT-PV-63989 • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3b; Vöhringer Coll.; MB.C.31150 • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Weyer 1993–1994 Coll.; MB.C.31151.2 .

Description

Holotype MB.C.31151.1 is a rather well-preserved specimen with 37 mm conch diameter, showing two complete whorls ( Fig. 70B ). The conch is thinly discoidal and evolute (ww/dm = 0.43; uw/dm = 0.48) with rather a low coiling rate (WER = 1.74). The whorl profile is kidney-shaped (ww/wh = 1.28) with a broadly rounded venter that merges continuously with the rounded flanks and the rounded umbilical wall.

Large areas of the specimen are covered with shell remains. These show lamellar growth lines, which are already directed backwards at the umbilical seam; they extend in this direction across the flank and then form a shallow ventral sinus ( Fig. 71D ). The growth lines are coarsest on the flank, while they are only visible as fine lines on the venter. Shell constrictions spaced at slightly more than 90 degrees extend parallel to the growth lines. These constrictions are more prominent on the inner mould than on the shell surface.

The cross sections of specimens MB.C.31150 (30.5 mm dm; Fig. 71A ), GPIT-PV-63942 (25.5 mm dm; Fig. 71B ) and GPIT-PV-63989 (17 mm dm; Fig. 71C ) show that the conch morphology experiences only minor changes above a conch diameter of 5 mm ( Fig. 71E–G ). The relative umbilical width remains the same at a value of about 0.50 and the ratio of whorl width and whorl height decreases only slightly from a value of 1.50 to 1.40. The coiling rate increases from 1.50 to 1.70.

Remarks

Gattendorfia bella sp. nov. can easily be distinguished from the other species of the genus because the conch ontogeny undergoes only insignificant changes; all other species show a marked decrease in relative umbilical width from about 15 mm conch diameter onwards, while the umbilicus in G. bella retains about the same opening rate. A similar species is only G. valdevoluta sp. nov.; however, in this species the growth lines are much finer and the umbilicus is more open in the juvenile stage (uw/dm ~0.65 at 5 mm dm in contrast to ~ 0.55 in G. bella ).

Figures

Fig. 70. Gattendorfia bella sp. nov. from the Oberrödinghausen railway cutting. A. Paratype MB.C.31151.2 (Weyer 1993–1994 Coll.) from bed 3e. B. Holotype MB.C.31151.1 (Weyer 1993–1994 Coll.) from bed 3e. Scale bar units=1 mm.

Fig. 71. Gattendorfia bella sp. nov. from the Oberrödinghausen railway cutting. A. Cross section of paratype MB.C.31150 (Vöhringer Coll.) from bed 3b. B. Cross section of paratype GPIT-PV-63942 (Vöhringer Coll.) from bed 3d. C. Cross section of paratype GPIT-PV-63989 (Vöhringer Coll.) from bed 5. D. Growth line course of holotype MB.C.31151.1 (Weyer 1993–1994 Coll.) from bed 3e, at dm =30.6 mm, ww = 8.5 mm, wh =13.8 mm. E–G. Ontogenetic development of the conch width index (ww/dm), umbilical width index (uw/dm), whorl width index (ww/wh) and whorl expansion rate (WER) of selected specimens. Scale bar units =1 mm.