Onychites quenstedti Engeser, 1987

Hammer, Øyvind, Hryniewicz, Krzysztof, Hurum, Jørn H., Høyberget, Magne, Knutsen, Espen M. & Nakrem, Hans A., 2013, Large onychites (cephalopod hooks) from the Upper Jurassic of the Boreal Realm, Acta Palaeontologica Polonica 58 (4), pp. 827-835 : 832-834

Onychites quenstedti Engeser, 1987

Figs. 3 , 4 .

1857 Onychites barbatus n. sp.; Quenstedt 1857: 804; pl. 99: 15.

cf. 1857 Onychites runcinatus n. sp.; Quenstedt 1857: 247; pl. 34: 4. 1912 Acanthoteuthis sp. ; Sokolov 1912: 10; pl. 1: 55.

1953 “ Onychites ” type I; Donovan 1953: 76–78; fig. 6a; pl. 15: 3–5. cf. 1953 “ Onychites ” type II; Donovan 1953: 76–78; fig. 6b; pl. 15: 6–7.

1987 Onychites quenstedti n. sp.; Engeser 1987: 14; pl. 2: 2, 4, 5. 1995 “Donovan−type” of onychite; Christensen 1995: pl. 1: 4, 5.

1999 Onychites barbatus Quenstedt, 1857 ; Schweigert 1999: pls. 5: 2, 5; 7: 1.

Material.—PMO 223.380 ( Fig. 3A, B ). This specimen was collected from a hydrocarbon seep carbonate near the top of the Slottsmøya Member at Knorringfjellet, Spitsbergen ( Hammer et al. 2011). Based on ammonite biostratigraphy, Wierzbowski et al. (2011) dated this particular carbonate body, seep no. 13, to the earliest Late Volgian. The shaft of the hook is preserved in three dimensions, while the uncinus is broken off, leaving a carbonaceous film. Length 3.2 cm (tip missing). PMO 223.378 ( Fig. 3C ). Level − 4 m, latest Early Volgian, Slottsmøya Member, Agardfjellet Formation, Janusfjellet, Spitsbergen. Basal part broken off. 4.0 cm long, external, flattened mould with thin carbonaceous film. PMO 223.379 ( Fig. 3D ), level − 4 m, latest Early Volgian, Slottsmøya Member, Agardhfjellet Formation, Janusfjellet, Spitsbergen. A complete hook, 4.3 cm long, preservation similar to PMO 223.378. PMO 223.382 ( Fig. 3E ). Level 14.6 m, Middle Volgian, Slottsmøya Member, Agardhfjellet Formation, Janusfjellet, Spitsbergen. A nearly complete hook with only a small part of the inner spur missing, 3.4 cm long, somewhat flattened, carbonaceous preservation. A relatively large number of additional, fragmented specimens were observed at the same stratigraphic level. PMO 210.229 ( Fig. 3F ). Statoil well 7/4−1, depth 3020.1 m, latest Early–early Middle Volgian, Farsund Formation, North Sea. Complete hook, 3.6 cm long. Preservation mainly as PMO 223.378, but with part of the shaft preserved in prismatic carbonaceous material. PMO 223.383 ( Fig. 3G ). Saga well 34/7−23A, depth 3284.5 m, Late Jurassic, Draupne Formation, northern North Sea. Nearly complete hook (tip missing), 2.8 cm long, preservation as PMO 210.229. PMO 74149 ( Fig. 3H ). Unknown level in drill core, Late Jurassic, “middle beds”, Andøya, northern Norway. 4.0 cm long, preservation as PMO 210.229. Illustrated by Sokolov (1912; pl. 1 fig. 5). PMO 223.381 ( Fig. 4 ). Probably from the Oppdalsåta Member (Kimmeridgian) of the Agardhfjellet Formation, Sassenfjorden area, Spitsbergen. Siltstone slab with three overlapping hooks, each ca. 2 cm long, preserved as carbonaceous films, but two of the hooks retain their tips relatively unflat−

tened. Description.—Variable size; 0.8–0.95 cm long in Germany

( Engeser 1987), circa 2 cm long in the Kimmeridgian of Spitsbergen (PMO 223.381), much larger, up to 4.4 cm, in the remaining Boreal material. Large curvature proximally (shaft), increasing distally (uncinus), approximating to a logarithmic spiral with the centre situated proximally. Whorl expansion rates variable, circa 0.5–1.5 (inner) and 0.3–0.7 (outer). Slender, lanceolate, tip of uncinus very sharp, nearly touching or projecting slightly beyond a line drawn through the base. Cross section lenticular. Inner spur short, robust, rounded, outer spur rudimentary or absent (slightly more extended in Germany; Engeser 1987). Base nearly straight or slightly convex. Orbicular scar (sensu Engeser 1987) broad but quite distinguishable, situated roughly half−way up the basal area. Shaft covered with weak, circular tubercles near the base, uncinus with weak chevron−type ornamentation in a herring−bone (reticulate) pattern.

Remarks.—The mega−onychites O. runcinatus as illustrated by Quenstedt (1857) in his pl. 34: 4 is identical with the material described herein. However, Engeser (1987) could not locate this specimen in the collections at Tübingen, and also observed that it does not resemble the O. runcinatus shown as fig. 5 on the same plate. He therefore removed this specimen from O. runcinatus .

A specimen of O. barbatus illustrated in the same volume ( Quenstedt 1857: pl. 99: 15) is also a close match. Engeser (1987), however, observed that the specimens included in O. barbatus by Quenstedt (1857) belong to more than one form species, and erected O. quenstedti for the one resembling our material (but see also Schweigert [1999] for taxonomical comments on O. barbatus and the priority of Fraas [1855] for the species name). The three hooks on PMO 223.381 are more than twice the size of Engeser’s (1987) illustrated specimens ( Schweigert 1999: pl. 6: 5 shows a larger specimen), have slightly more rounded, shorter internal spurs, and external spurs are practically absent, but these differences do not appear sufficient to separate the three hooks from O. quenstedti . The whorl expansion rates are also very similar ( Fig. 8 ).

Our remaining Boreal mega−onychites have considerably larger whorl expansion rates and are also much larger in size than the type O. quenstedti , but we do not find sufficient grounds for erecting a new form species for them. Sokolov (1912) appears to be the first author to describe this larger form, from the Upper Jurassic of Andøya, northern Norway. Sokolov claimed a similarity to Onychites Fraarsi (sic!) Quenstedt, 1857, however, O. fraasi is of completely different shape with an enormous inner spur, and is only a third the size. He suggested the hook came from the belemnoid Acanthoteuthis , but this was probably based only on the general fact that arm hooks had been observed on Acanthoteuthis specimens with soft−body preservation. However, these are small and of totally different shape, with long and straight shaft and weakly curved uncinus ( Donovan and Crane 1992; Fuchs 2006).

Donovan (1953) described five specimens of mega−onychites from the Kimmeridgian of Greenland. Referring to the hooks figured on plate 24 in Quenstedt’s (1857) monograph, he did not find a perfect match, and therefore used open nomenclature. The similar hooks figured by Christensen (1995) were referred to by him as “Donovan−type”. However, as mentioned above, we see strong similarity with hooks illustrated on other plates in Quenstedt (1857).

Geographic and stratigraphic range.—Possibly Lower Toarcian of Germany (the lost “ O. runcinatus ” illustrated by Quenstedt 1857); Upper Kimmeridgian to Lower Tithonian of Nusplingen, Germany ( Quenstedt 1857; Engeser 1987; Schweigert 1999);?Lower Kimmeridgian of East Greenland (Dono−

http://dx.doi.org/10.4202/app.2012.0020

van 1953); Draupne Formation spanning the Kimmeridgian– Ryazanian in the northern North Sea ( Christensen 1995); Lower–Middle Volgian Farsund Formation in the North Sea; Volgian at Andøya, northern Norway ( Sokolov 1912); Volgian Agardhfjellet Formation in the Sassenfjorden area, Spitsbergen (herein);?Kimmeridgian of the Agardhfjellet Formation in the Sassenfjorden area, Spitsbergen (herein).

Figures

Fig. 3. Belemnoid mega−onychites Onychites quenstedti Engeser, 1987 from Boreal localities. A. PMO 223.380, seep carbonate, earliest Late Volgian, Knorringfjellet, Spitsbergen; entire specimen. B. Close−up of shaft on PMO 223.380, showing rows of circular tubercles. C. PMO 223.378, latest Early Volgian, Janusfjellet, Spitsbergen. D. PMO 223.379, latest Early Volgian, Janusfjellet, Spitsbergen. E. PMO 223.382, Middle Volgian, Janusfjellet, Spitsbergen. F. PMO 210.229, latest Early or early Middle Volgian, well 7/4−1, North Sea. G. PMO 223.383, Late Jurassic, well 34/7−23A, North Sea. H. PMO 74149, Late Jurassic, Andøya, northern Norway.

Fig. 4. Belemnoid mega− (Onychites quenstedti Engeser, 1987) and microonychites from the Agardhfjellet Formation (probably Oppdalsåta Member), Upper Jurassic, Spitsbergen. PMO 223.381. A. Photograph. B. Explanatory drawing. Micro−onychites marked as hooks (complete specimens), lines and dots (incomplete specimens). Density of micro−onychites in gray scale, computed using the kernel density method.

Fig. 8. Whorl expansion coefficients (b) for inner and outer spirals. Onychites quenstedti as figured by Engeser (1987: pl. 2: 5).