Gattendorfia valdevoluta, 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 : 123-125

Gattendorfia valdevoluta sp. nov.

urn:lsid:zoobank.org:act:3C3A26D9-674D-43A2-9FED-DDE94DC01888

Figs 72–73 ; Tables 70–71

Gattendorfia tenuis – Vöhringer 1960: 153, text-fig. 28. — Korn 1994: 75, text-figs 66e.

Diagnosis

Species of Gattendorfia with a conch reaching 50 mm diameter. Conch at 5 mm dm extremely discoidal, very evolute (ww/dm ~0.30; uw/dm ~0.65); at 15 mm dm thinly discoidal, evolute (ww/dm ~0.40; uw/ dm ~0.50); at 40 mm dm thinly discoidal, subevolute (ww/dm ~0.40; uw/dm ~0.40). Whorl profile in the juvenile stage depressed oval, at 40 mm dm weakly depressed (ww/wh ~1.10); coiling rate low (WER ~1.70). Venter broadly rounded throughout ontogeny, umbilical margin narrowly rounded in the adult stage. Growth lines fine, narrow-standing, with convex course. Deep constrictions on the shell surface, prominent internal shell thickenings.

Etymology

From the Latin ‘ valte ’ = ‘very’ and ‘ evoluta ’ = ‘evolute’; referring to the extremely evolute juvenile conch.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3d2; Weyer 1993–1994 Coll.; illustrated in Fig. 72A ; MB.C.31155.

Paratypes

GERMANY • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 2; Vöhringer Coll.; GPIT-PV-63996 • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3a; Vöhringer Coll.; MB.C.31152 • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; MB.C.31153 • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 2b; Weyer 1993–1994 Coll.; MB.C.31154 .

Description

Holotype MB.C.31155 has a diameter of 17 mm and is preserved with some shell remains ( Fig. 72A ). The conch is serpenticonic with a very wide umbilicus (ww/dm = 0.42; uw/dm = 0.55). The whorl profile is kidney-shaped (ww/wh = 1.46) with broadly rounded venter and flanks; the umbilical margin is broadly rounded and the umbilical wall is convex. The shell bears fine growth lines, which are slightly directed backwards on the flank and run with a very shallow sinus across the venter ( Fig. 73D ). There are several shell constrictions that follow the course of the growth lines. These constrictions are arranged in nearly regular distances of 90 degrees, so they have a position almost at the same angle on the last two whorls.

Paratype MB.C.31154 has 11 mm diameter and is serpenticonic like the inner whorls of the holotype ( Fig. 72B ). A difference from the holotype is, however, that the specimen has irregularly distributed constrictions; the last two of them are arranged at right angles to each other.

The sectioned specimen GPIT-PV-63996 shows the ontogenetic development of the conch morphology from the initial stage to 32 mm diameter ( Fig. 73A ). The conch begins with a serpenticonic morphology and has a rounded-trapezoidal whorl profile that changes into a broad oval profile at about 7 mm conch diameter. At about 14 mm diameter there is a rapid increase in whorl height and at 32 mm diameter, the width of the profile is only slightly greater than the height. At this stage there is already quite a distinct umbilical edge from which the flanks converge to the relatively narrow venter.

The ontogenetic trajectories show moderate changes in the cardinal conch parameters ( Fig. 73E–G ). The ww/dm and uw/dm trajectories are biphasic and run diametrically; the ww/dm ratio is lowest at about 4 mm dm (~0.30), while the uw/dm ratio is highest (~0.65). At 18 mm dm, both values are about equal (~0.50). The width of the whorl profile decreases smoothly from ~1.80 to ~1.50 between 2 and 20 mm conch diameter; thereafter the decrease is slightly more rapid to ~1.10 at 32 mm dm.

Remarks

Gattendorfia valdevoluta sp. nov. is, according to present knowledge, the species of the genus with the widest umbilical opening in the juvenile stage; the uw/dm ratio exceeds the value of ~0.65 at 5 mm conch diameter. This ratio reaches, in other discoidal species, only ~ 0.55 in G. rhenana sp. nov. and G. bella sp. nov. or ~ 0.60 in G. schmidti sp. nov. However, G. valdevoluta clearly differs from G. schmidti in the course of the constrictions, which are almost straight and slightly backwardly directed on the flank in G. valdevoluta , but in G. schmidti they extend with a concavo-convex course.

Figures

Fig. 72. Gattendorfia valdevoluta sp. nov. from the Oberrödinghausen railway cutting. A. Holotype MB.C.31155 (Weyer 1993–1994 Coll.) from bed 3d2. B. Paratype MB.C.31154 (Weyer 1993–1994 Coll.) from bed 2b. Scale bar units= 1 mm.

Fig. 73. Gattendorfia valdevoluta sp. nov. from the Oberrödinghausen railway cutting. A. Cross section of paratype GPIT-PV-63996 (Vöhringer Coll.) from bed 2. B. Cross section of paratype MB.C.31152 (Vöhringer Coll.) from bed 3a. C. Cross section of paratype MB.C.31153 (Vöhringer Coll.) from bed 3d. D. Growth line course of holotype MB.C.31155 (Weyer 1993–1994 Coll.) from bed 3d2, at dm =17.0 mm, ww =7.0 mm, wh=4.8 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.