Zadelsdorfia crassa ( Schmidt, 1924 )

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 : 136-143

Zadelsdorfia crassa ( Schmidt, 1924)

Figs 80–85 ; Tables 78–79

Gattendorfia crassa Schmidt, 1924: 151 , pl. 8 figs 9–11.

Gattendorfia crassa – Schmidt 1925: 535, pl. 19 fig. 9. — Librovitch 1940: pl. 4 fig. 4. — Pfeiffer 1954: 100, pl. 7 fig. 3. — Vöhringer 1960; 154, pl. 4 figs 1–4, pl. 5 fig. 8, text-figs 30, 36. — Weyer 1965: 447, pl. 7 fig. 1. — Popov 1975: 115, pl. 36 fig. 9, pl. 46 fig. 8. — Bartzsch & Weyer 1982: 21, text-fig. 6. — House 1985a: 126, pl. 6.7.14 fig. c. — Bartzsch & Weyer 1986: pl. 2 fig. 3. — Korn 1994: 73, text-figs 66b–c, 67b, 68a, 69a–d; 2006: text-fig 3k. — Dzik 1997: 107, text-fig. 28g. — Kullmann 2000: text-fig. 4k. — Sprey 2002: 53, text-fig. 18e. — Korn & Vöhringer 2004: 426, text-figs 3–4, 6.

non Gattendorfia crassa – Librovitch 1940: 45, pl. 4 figs 1–3. — Schindewolf 1952: 296, pl. 2 fig. 5. — Bockwinkel & Ebbighausen 2006: 109, text-figs 26, 27g –j.

Diagnosis

Species of Zadelsdorfia with a conch reaching 70 mm diameter. Conch at 5 mm dm thinly discoidal, very evolute (ww/dm = 0.35–0.45; uw/dm = 0.60–0.65); at 15 mm dm thickly discoidal to thinly pachyconic, evolute (ww/dm = 0.55–0.65; uw/dm = 0.45–0.55); at 40 mm dm thickly discoidal to thinly pachyconic, subinvolute (ww/dm = 0.55–0.65; uw/dm ~0.20–0.30). Whorl profile in the juvenile stage depressed oval, at 40 mm dm weakly depressed (ww/wh = 1.20–1.50); coiling rate low to moderately high (WER = 1.60–1.80). Venter flattened in the juvenile stage, umbilical margin subangular in the adult stage. Growth lines lamellar, wide-standing, with convex course. Faint constrictions on the shell surface and prominent internal shell thickenings. Suture line with lanceolate, weakly pouched external lobe and V-shaped adventive lobe.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone ; Schmidt Coll.; illustrated by Schmidt (1924: pl. 8 figs 9–11), Korn & Vöhringer (2004: text-fig. 3) and Korn (2006: text-fig. 3k); re-illustrated here in Fig. 80 ; BGR X5714.

Additional material

GERMANY • 9 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 2 ; Vöhringer Coll.; GPIT-PV-63924, GPIT-PV-63944–GPIT-PV-63945, GPIT-PV-63947, GPIT-PV-63953–GPIT-PV-63957 • 30 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 2 ; Vöhringer Coll.; MB.C.5346–MB.C.5358, MB.C.31166.1– 17 • 2 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3b; Vöhringer Coll.; MB.C.31167.1–2 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , loose material; Vöhringer Coll.; MB.C.31168 • 3 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , loose material; Korn 1977 Coll.; MB.C.31169.1–3 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 2 ; Weyer 1993–1994 Coll.; MB.C.31170 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 2 a; Weyer 1993–1994 Coll.; MB.C.31171 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3b; Weyer 1993–1994 Coll.; MB.C.31172 • 1 specimen; Rhenish Mountains, Oberrödinghausen , road cutting; Hangenberg Limestone , bed 3b; Korn & Weyer 2000 Coll.; MB.C.31173.

Description

Holotype BGRB X5714 is a slightly deformed specimen with 45 mm conch diameter ( Fig. 80 ) that has fallen apart; however, several pieces of the inner whorls show the characteristic conch and ornamental features of the species. At a diameter of 45 mm, the conch is thinly pachyconic (ww/dm ~0.68 after correction of deformation) and thus belongs to the stouter specimens within the species. The umbilicus is moderately narrow (uw/dm ~0.27); the umbilical margin is subangular and separates the broadly rounded flanks from the steep, slightly flattened umbilical wall. The shell surface bears lamellar, irregularly distributed, sharp growth lines on the flanks with a convex, backwardly directed course. They form a broadly V-shaped ventral sinus. One narrow shell constriction can be seen; it largely follows the course of the growth lines and is present on flanks and venter.

The four specimens GPIT-PV-63953, GPIT-PV-63955, GPIT-PV-63957 and GPIT-PV-63947 give an insight into the conch morphology and intraspecific variation between 30 and 57 mm conch diameter ( Fig. 81 ). These specimens show the differences in the width ratio of the conch, in the expression of the growth lines and the constrictions. Specimen GPIT-PV-63953 is most similar to the holotype with regard to the ornament. It has only two constrictions on the last whorl; the first begins on the inner half of the flank and is clearly less pronounced on the shell surface than on the internal mould. The second constriction follows 90 degrees later and is restricted to the venter ( Fig. 81A ).

The two smaller specimens MB.C.31169.2 (18.8 mm dm; Fig. 83B ) and MB.C.31169.1 (23 mm dm; Fig. 83A ) demonstrate the variation in the ontogenetic conch development within the species, as outlined by Korn & Vöhringer (2004). The uw/dm ratio is, at 18.8 mm dm, ~ 0.51 in specimen MB.C.31169.2 but only ~0.40, at 23 mm dm, in specimen MB.C.31169.1, meaning that the latter specimen had a slightly faster ontogenetic development and passed through the evolute stage at a smaller conch diameter. Both specimens show lamellar growth lines with backwardly directed course and shell constrictions of variable strength; they follow the course of the growth lines.

The extensive material with a total of 17 cross sections ( Figs 84A–B , 85 ) allows a detailed study of conch ontogeny and intraspecific variation ( Korn & Vöhringer 2004). The trajectories of the individual conch parameters show the following characteristics:

The ontogenetic trajectories of the ww/dm ratio show a triphasic development ( Fig. 84E ). They describe a rapid decrease in the value to ~0.35 at 5 mm conch diameter, then increasing again to an average value of ~0.70 at 25 mm dm and finally decreasing again to ~0.55 at 55 mm dm. The variation is about the same in all stages of growth.

The uw/dm ratio undergoes striking ontogenetic changes, which can be seen in the illustrations of the cross-sections ( Fig. 84E ). In the early stages, the umbilicus has a width of ~0.30 of the conch diameter. Up to a diameter of about 3.5 mm, a continuous increase can be observed; between 3.5 and 9 mm diameter, the median value of the uw/dm ratio is greater than 0.60. Specimens larger than 9 mm then show a relatively steady decrease, so that at 40 mm diameter, the umbilicus has a width of only ~0.20 of the conch diameter. This value shows little intraspecific variation; the variation is greatest at the stage between 3 and 15 mm.

The ww/wh diagram clearly shows ontogenetic changes in the shape of the whorl profile. After an initial decline, a minimum value (~1.65) is reached at a conch diameter of 2.5 mm. Between 2.5 and 10 mm diameter there is a continuous increase to a median value of ~2.00, while for diameters greater than 15 mm there is a marked decrease to about 1.20 at 40 mm diameter ( Fig. 84F ). The intraspecific variation is not particularly high at any growth stage. As for the uw/dm ratio, the middle stages, between 7 and 20 mm diameter of the conch, are less variable than for the early juveniles and adults.

During ontogenetic development, the coiling rate (WER) shows only slight fluctuations ( Fig. 84G ). The coiling rate has highest values in the early juvenile stage at a conch diameter up to 2 mm (median value 1.70–1.80). During early ontogeny, this value decreases to less than 1.50 at stages between 5 and 8 mm diameter, and increases again at the adult stage, reaching a value of ~1.75 at 40 mm conch diameter. The intraspecific variation is relatively low at all growth stages. In the intermediate stages between 4 and 16 mm conch diameter, there is a tendency towards slightly lower variation, but the differences between the growth stages are inconspicuous.

Remarks

Material from the type locality was described in detail by Vöhringer (1960) and in greater detail by Korn & Vöhringer (2004). Thanks to the many well-preserved specimens available, Zadelsdorfia crassa is a well-known species and can be characterised by the morphology and ontogenetic development of the conch.

Zadelsdorfia crassa belongs to the stout, in the adult stage rather narrowly umbilicate species of the subfamily Gattendorfiinae and is thus easily distinguishable from most of the other species. Species with stout conch are G. costata (with much wider umbilicus) and Z. oblita sp. nov. (with concavo-convex constrictions). Among the species from the Rhenish Mountains, G. corpulenta sp. nov. has the most similar morphology, but possesses short, sharp riblets on the inner flank half. Furthermore, G. corpulenta is stouter at the adult stage (ww/dm ~0.80 at 30 mm dm, but only ~ 0.65 in Z. crassa ).

Zadelsdorfia crassa has been mentioned several times from other regions, but it is not clear whether these specimens actually belong to this species. The following mentions of presumed occurrences of Z. crassa are probably not correct:

Librovitch (1940): The specimens shown are much too narrowly umbilicate; they have an almost closed umbilicus and are therefore clearly distinguishable from Z. crassa .

Bockwinkel & Ebbighausen (2006): The specimens are smaller than the type material, for example the largest specimen shown has only 18 mm diameter. At this stage, the Moroccan material is a little more narrowly umbilicate. The same applies to the cross sections shown. The main difference, however, can be seen in the course of the constrictions, which in the Anti-Atlas specimens are straight or extend with a very shallow sinus across the flank and form a shallow ventral sinus.

Figures

Fig. 80. Zadelsdorfia crassa (Schmidt, 1924), holotype BGRB X5714 (Schmidt 1920 Coll.) from the Oberrödinghausen railway cutting. Scale bar units=1 mm.

Fig. 81. Zadelsdorfia crassa (Schmidt, 1924) from bed 2 of the Oberrödinghausen railway cutting, all Vöhringer Coll. A. Specimen GPIT-PV-63953. B. Specimen GPIT-PV-63955. C. Specimen GPIT- PV-63957. D. Specimen GPIT-PV-63947. Scale bar units =1 mm.

Fig. 82. Zadelsdorfia crassa (Schmidt, 1924), paratype GPIT-PV-63954 (Vöhringer Coll.) from the Oberrödinghausen railway cutting, bed 2. Photograph of the unwhitened specimen showing exemplary the often poorly preserved shell surface of the material from Oberrödinghausen. Scale bar units =1 mm.

Fig. 83. Zadelsdorfia crassa (Schmidt, 1924) from the Oberrödinghausen railway cutting, both Korn 1977 Coll. A. Specimen MB.C.31169.1. B. Specimen MB.C.31169.2. Scale bar units=1 mm.

Fig. 84. Zadelsdorfia crassa (Schmidt, 1924) from the Oberrödinghausen railway cutting. A. Cross section of specimen GPIT-PV-63944 from bed 2. B. Cross section of specimen MB.C.5355 from bed 2. C. Suture line of specimen GPIT-PV-63955 from bed 2, at dm =35.0 mm, ww = 23.5 mm, wh =14.5 mm. D. Growth line course of specimen GPIT-PV-63953 from bed 2, at wh =24.0 mm ww, wh =16.0 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.

Fig. 85. Zadelsdorfia crassa (Schmidt, 1924) from the Oberrödinghausen railway cutting, cross sections, bed 2; all Vöhringer Coll. A. Specimen MB.C.5347.B. Specimen MB.C.5348. C. Specimen MB.C.5346. D. Specimen GPIT-PV-63956. E. Specimen MB.C.5349. F. Specimen MB.C.5353. G. Specimen MB.C.5351. H. Specimen MB.C.5352. I. Specimen MB.C.5350. J. Specimen MB.C.31166.1. K. Specimen MB.C.5354. L. Specimen MB.C.5358. M. Specimen MB.C.5357. N. Specimen MB.C.5356. O. Specimen MB.C.31166.2. Scale bar units =1 mm.