Eocanites nodosus ( Schmidt, 1925 )

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 : 196-199

Eocanites nodosus ( Schmidt, 1925)

Figs 119–120 ; Tables 113–114

Gattendorfia nodosa Schmidt, 1925: 536 , pl. 19 fig. 10, pl. 23 fig. 2.

Protocanites nodosus – Vöhringer 1960: 169, pl. 6 fig. 1a, text-fig. 44b.

Protocanites (Eocanites) nodosus – Weyer 1965: 457, pl. 7 fig. 4.

Eocanites nodosus – Weyer 1977: 173, pl. 1 fig. 4. — Korn 1994: 81, text-figs 73a–b, d, 74a, 75c; 2006, text-fig. 4h. — Dzik 1997: 108, text-fig. 29b. — Sprey 2002: pl. 4 fig. 6.

non Gattendorfia nodosa Schmidt, 1925: 536 , pl. 19 fig. 10, pl. 23 fig. 3.

non Protocanites nodosus – Vöhringer 1960: 169, pl. 6 fig. 1b, text-fig. 44a.

non Eocanites nodosus – Korn 1997: 33, pl. 1 figs 4–5, text-fig. 18. — Korn & Feist 2007: 108, text-fig. 6f.

Diagnosis

Species of the genus Eocanites with a conch reaching 35 mm diameter. Conch at 12 mm dm evolute (uw/dm ~0.50) with a weakly depressed whorl profile (ww/wh ~1.05) and a broadly rounded venter; conch at 30 mm dm evolute (uw/dm ~0.50) with weakly compressed whorl profile (ww/wh ~0.90) and broadly rounded venter. Ornament with coarse, strongly rursiradiate, biconvex, crenulated growth lines with deep ventral sinus. Ornament without ribs or nodes. Suture line with lanceolate external lobe and asymmetric, dorsally pouched adventive lobe.

Material examined

Lectotype

GERMANY • Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone ; Schmidt Coll.; designated by Vöhringer (1960); illustrated by Schmidt (1925: pl. 23 fig. 2), re-illustrated here in Fig. 119D ; GZG.INV.1689.

Additional material

GERMANY • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3c; Vöhringer Coll.; GPIT-PV- 63968 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3d; Vöhringer Coll .; GPIT-PV- 63972 • 1 specimen; Rhenish Mountains, Oberrödinghausen , west of railway cutting ; Hangenberg Limestone , loose material; Korn 1977 Coll .; MB.C. 31232 • 2 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3d1; Weyer 1993–1994 Coll.; MB.C. 31233.1–2 • 15 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3d1b; Weyer 1993–1994 Coll.; MB.C. 31234.1–15 • 3 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3d2; Weyer 1993–1994 Coll.; OR- MB.C. 31235.1–3 • 1 specimen; Rhenish Mountains, Hasselbachtal ; Hangenberg Limestone , bed 71; Weyer 1993–1994 Coll.; MB.C. 5244.2 .

Description

Lectotype GZG.INV.1689 has a conch diameter of 17.5 mm and possesses coarse, crenulated growth lines, but no ribs ( Fig. 119D ). Although more than 20 specimens are available, none is larger than 25 mm. The largest specimen GPIT-PV-63968 is still chambered at 19 mm conch diameter ( Fig. 119A ); therefore the total size including body chamber can be estimated at about 35 mm.

The three specimens GPIT-PV-63968 (25 mm dm; Fig. 119A ), GPIT-PV-63972 (20 mm dm; Fig. Fig. 119B ) and MB.C.31234.1 (19 mm dm; Fig. 119C ) show very similar dimensions and conch proportions like the lectotype. They are very discoidal and serpenticonic (ww/dm = 0.28–0.36; uw/ dm = 0.46–0.48) with a more or less circular whorl profile (ww/wh = 0.93–1.14). All three show a rather coarse ornament with coarse growth lines directed backwards on the flank, between which finer spiral lines are formed. The growth lines themselves are not crossed by the spiral lines and therefore do not show granulation. The course of the growth lines is biconvex and rursiradiate.

The sectioned specimen MB.C.31234.2 allows the study of conch ontogeny up to 22 mm diameter ( Fig. 120A ). At all stages the whorl profile has a similar shape; it is widest at the broadly rounded umbilical margin and shows weakly converging flanks and a broadly rounded venter.

The ontogenetic trajectories of the cardinal conch parameters are rather simple ( Fig. 120D–F ). The uw/ dm ratio remains almost constant between 1 and 25 mm conch diameter at a value around 0.50 and the whorl expansion rate is stable at about 1.80. In contrast to this, the shape of the whorl profile changes continuously; the ww/wh ratio decreases from about 2.15 to 0.93. Correspondingly, the ww/dm ratio also decreases from ~0.60 to ~0.30.

The suture line of specimen GPIT-PV-63968 has a lanceolate, rather distinctly pouched external lobe, an inflated ventrolateral saddle and a distinctly asymmetric adventive lobe. This has a vertical, sigmoidal ventral flank and a very strongly sigmoidal dorsal flank ( Fig. 120B ). The lateral lobe is small and V-shaped.

Remarks

Schmidt (1925) as well as Vöhringer (1960) and Korn (1994) united two forms under the species Eocanites nodosus ; they assumed that the ribbed adult stage with concave venter belongs to the subadult form with very coarse, crenulated growth lines. However, there is no evidence for this assumption, because the ribbed species E. ruani already has an almost rectangular profile and strong radial ribs at a whorl height of 10 mm, where specimens of E. nodosus do not possess ribs. The selection of the lectotype led to the somewhat peculiar situation that the species name E. nodosus is now used not for the nodose form (later described as E. ruani ), but for the non-nodose form.

Figures

Fig. 119. Eocanites nodosus (Schmidt, 1925) from the Oberrödinghausen railway cutting. A. Specimen GPIT-PV-63968 (Vöhringer Coll.) from bed 3d. B. Specimen GPIT-PV-63972 (Vöhringer Coll.) from bed 3d. C. Specimen MB.C.31234.1 (Weyer 1993–1994 Coll.) from bed 3d1b. D. Reproduction of the figure of “Gattendorfia nodosa” of Schmidt (1925, pl. 23 fig. 2). Scale bar units =1 mm.

Fig. 120. Eocanites nodosus (Schmidt, 1925) from the Oberrödinghausen railway cutting. A. Cross section of specimen MB.C.31234.2 (Weyer 1993–1994 Coll.) from bed 3d1b. B. Suture line of specimen GPIT-PV-63968 from bed 3d, at dm =18.6 mm, ww =5.5 mm, wh=5.5 mm. C. Growth line course of specimen GPIT-PV-63968 from bed 3d, at dm= 22.5 mm, ww =6.4 mm, wh =6.9 mm. D–F. 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.