Gattendorfia immodica, 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 : 134-135

Gattendorfia immodica sp. nov.

urn:lsid:zoobank.org:act:C0E69971-2116-4291-9613-997B27B43F6B

Fig. 79 ; Table 77

Diagnosis

Species of Gattendorfia with a globular, evolute conch (ww/dm ~0.90; uw/dm ~0.50) at 10 mm dm. Whorl profile at 10 mm dm extremely depressed (ww/wh ~3.00); coiling rate low (WER ~1.65). Venter flattened, umbilical margin pronounced. Without constrictions on the shell surface and without internal shell thickenings, with parabolic ribs on the umbilical margin.

Material examined

Holotype

GERMANY • Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 5a2; Weyer 1993–1994 Coll.; illustrated in Fig. 79 ; MB.C.31165.

Etymology

From the Latin adjective ‘ immodica ’ = ‘immoderate’, referring to the extraordinary conch shape.

Description

Holotype MB.C.31165 (nearly 11 mm dm) demonstrates the spectacular conch morphology of the immature stage ( Fig. 79 ). It has the shape of a thick barrel (ww/dm ~0.90) and is evolute (uw/dm ~0.50) with a strongly depressed whorl profile (ww/wh ~3.00). Furthermore, the whorl profile possesses a raised umbilical wall that is accompanied on the umbilical and the flank side by an incurved shell portion of the shell wall. It separates the sinuous umbilical wall from the broad, flattened area of flanks and venter.

The shell surface bears lamellar growth lines running backwards along the umbilical wall; they are coarsest where they cross the raised umbilical margin. They extend in a broad and low arc across the venter. The umbilical wall of the last half volution bears six ribs, which turn back sharply, much more so than the growth lines, and thicken near the umbilical margin to form parabolic nodes. The penultimate whorl, visible in the umbilicus, also has nodes, but they are much sharper and less strongly directed backwards.

Remarks

There is no other ammonoid species known from the early Tournaisian that resembles Gattendorfia immodica sp. nov. The striking morphology in the juvenile stage, has not been seen in any other species of Gattendorfia in a cross section.

The only species that could be considered for comparison is G. costata , which is only known from Oberrödinghausen by one specimen of 30 mm conch diameter. The holotype of this species does not show the geometry of the inner whorls. However, it is very likely that the specimen from Saalfeld figured by Bartzsch & Weyer (1982: text-fig. 4.2) really belongs to G. costata ; this specimen allows for the study of some inner whorls, which here have a rounded umbilical margin.

Figures

Fig. 79. Gattendorfia immodica sp. nov. from the Oberrödinghausen railway cutting; photographs and dorsal view reconstruction of holotype MB.C.31165 (Weyer 1993–1994 Coll.) from bed 5a2. Scale bar units =1 mm.