Kornia acia, 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 : 41-43

Kornia acia sp. nov.

urn:lsid:zoobank.org:act:62D5E824-BACD-4D6F-B03E-2F09A89D9349

Figs 27–28 ; Tables 17–18

Diagnosis

Species of Kornia with globular to spindle-shaped, involute conch (ww/dm ~1.05; uw/dm ~0.10) at 12 mm conch diameter. Growth lines lamellar with moderately deep, wide ventral sinus.

Etymology

From the Latin ‘ acia ’ = ‘yarn’, as the conch has the shape of a yarn reel.

Material examined

Holotype

GERMANY • Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 5a2; Weyer 1993–1994 Coll.; illustrated in Fig. 27 ; MB.C.31073.1.

Paratypes

GERMANY • 1 specimen; Rhenish Mountains , Oberrödinghausen , road cutting; Hangenberg Limestone, P.dorsoplanus Zone ; Korn 1977Coll.; MB.C.31072 • 1specimen; Rhenish Mountains , Oberrödinghausen , railway cutting; Hangenberg Limestone, bed 5a2; Weyer 1993–1994 Coll.; MB.C.31073.2 .

Description

Holotype MB.C.31073.1 is a well-preserved specimen that is fully covered by shell material ( Fig. 27 ). It has a conch diameter of 12.3 mm and changes from spindle-shaped to globular in the last half whorl (ww/dm = 1.13 at 10 mm dm; ww/dm = 1.05 at 12.3 mm dm); the umbilicus is very narrow (uw/dm = 0.10 at 12.3 mm dm). The peculiar apertural shape shows a pronounced umbilical margin, from where the flanks, which are nearly arranged in right angles, rapidly converge towards the broadly rounded venter. The aperture is very low (WER = 1.47). The shell surface shows lamellar growth lines; they form a pronounced dorsolateral projection and turn back to proceed in a very wide and moderately deep sinus across flanks and venter ( Fig. 28B ). At a major non-lethal shell damage, the growth lines deviate from this course during the interval of repair.

Paratype MB.C.31072 was sectioned and allows the study of conch ontogeny up to a diameter of 19 mm ( Fig. 28A ). All whorls have a similar profile, but the ww/wh ratio decreases from about 3.00 at 1.5 mm conch diameter to about 1.80 at 19 mm diameter ( Fig. 28D ). At the same time, the shape of the profile changes from broad kidney-shaped to C-shaped. At all size stages, the flanks are strongly convergent and the venter is comparatively narrow. The umbilical margin is particularly pronounced between 4 and 10 mm conch diameter.

Remarks

Kornia acia sp. nov. cannot be confused with any other ammonoid from the Hangenberg Limestone because of its peculiar spindle-shaped juvenile conch with raised umbilical margin and the strongly backward directed growth lines. K. fibula sp. nov. has a ball shaped conch with more broadly rounded venter and a wider umbilicus than K. acia (uw/dm ~ 0.10 in K. acia but ~ 0.15 in K. fibula at 11–12 mm dm).

Kornia citrus from the Anti-Atlas has a very similar conch geometry, but differs from C. acia sp. nov. in the shape of the umbilical margin, which in K. citrus is more strikingly raised but more rouded in K. acia .

Figures

Fig. 27. Kornia acia sp. nov. from the Oberrödinghausen railway cutting; holotype MB.C.31073.1 (Weyer 1993–1994 Coll.) from bed 5a2. Scale bar units =1 mm.

Fig. 28. Kornia acia sp. nov. from Oberrödinghausen railway cutting; both Weyer 1993–1994 Coll. A. Cross section of paratype MB.C.31072 from an unknown bed. B. Growth line course of holotype MB.C.31073.1 (Weyer 1993–1994 Coll.) from bed 5a2, at dm= 11.1 mm, ww =11.6 mm, wh=5.3 mm. C–E. 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.