Rhynchorthoceras kranepuhlense, Aubrechtová & Korn, 2022

Aubrechtová, Martina & Korn, Dieter, 2022, Taxonomy and ontogeny of the Lituitida (Cephalopoda) from Orthoceratite Limestone erratics (Middle Ordovician), European Journal of Taxonomy 799 (1), pp. 1-108 : 26-27

Rhynchorthoceras kranepuhlense sp. nov.

urn:lsid:zoobank.org:act:C6275788-FF3A-4730-9E8B-237DC086E929

Figs 15B , 16 , Tables 2–3

Diagnosis

Species of the genus Rhynchorthoceras with expansion angles between 8° and 11°; whorl profile circular. Shell surface with transverse striae, up to 1 mm apart (at wh = 21 mm) and spaced irregularly. Conch slightly constricted, where the striae are finest. The striae extend oblique but straight laterally and directly transverse and straight ventrally, with a low projection dorsally. Siphuncle ca 0.12 in diameter, central or almost central in position.

Etymology

From the type locality Kranepuhl.

Type material

Holotype GERMANY • Brandenburg, Kranepuhl; Ordovician, Upper Red Orthoceratite Limestone (Aseri Regional Stage, middle Darriwilian); Kummerow Coll.; MB.C.11730 (illustrated in Fig. 15B ).

Paratypes GERMANY • 1 spec.; Brandenburg, Niederfinow; Ordovician, Upper Red Orthoceratite Limestone; Neben and Krueger Coll.; MB.C.30491 • 1 spec.; Brandenburg, Oderberg; Ordovician, Upper Red Orthoceratite Limestone; Neben and Krueger Coll.; MB.C.30492 .

POLAND • 1 spec.; West Pomerania, Dewitz Castle, Dobra ( former Dewitzburg bei Daber ); Ordovician, Upper Red Orthoceratite Limestone; MB.C.30493 .

Description

Holotype MB.C.11730 ( Fig. 15B ) is a fragment of an orthoconic phragmocone with 100 mm length. The conch has a circular whorl profile and expands with an angle of 11°. The shell ornament is preserved along the whole length of the specimen. It consists of transverse striae, which are up to 1.5 mm apart (at the maximum whorl height of 24 mm). The distance of the striae changes irregularly during ontogeny ( Fig. 16F–G ); at about 10 mm whorl height, the striae become extremely fine and the conch is slightly constricted at this position ( Fig. 15B ). The shell wall is slightly undulated in the second half of the specimen. The striae are oblique but straight on the flanks, completely transverse and straight on the venter; they possess a low projection on the dorsum ( Fig. 16A ). The siphuncle is seen at the latest preserved septum; it is narrow (0.12 of whorl height) and central in position.

Remarks

Rhynchorthoceras kranepuhlense sp. nov. is morphologically closest to R. rugium sp. nov. (described above) because of its striated shell surface. However, the striae in R. kranepuhlense sp. nov. stand much closer together and their distance is much more irregular. Also, at places where the distance of the striae is decreased, shallow conch constrictions ( Fig. 15B ) appear around the conch circumference.

Geographic and stratigraphic occurrence

Northern Germany and Poland (in erratics within Pleistocene gravels); late Kunda to early Lasnamägi regional stages (middle to late Darriwilian, Middle Ordovician).

Figures

Fig. 15.Species of Rhynchorthoceras from the Upper Red Orthoceratite Limestone.A. Rhynchorthoceras rugium sp. nov., holotype MB.C.11728 (Hoffmann & Gager 1972 Coll.) from Mönchgut (Island of Rügen); lateral, dorsal and ventral views. B. Rhynchorthoceras kranepuhlense sp. nov., holotype MB.C.11730 (Kummerow Coll.) from Kranepuhl (Brandenburg); ventral, lateral and dorsal views. Scale bar units = 1 mm.

Fig. 16. Rhynchorthoceras kranepuhlense sp. nov. from the Upper Red Orthoceratite Limestone. A. Striae of holotype MB.C.11730 (Kummerow Coll.) from Kranepuhl (Brandenburg), at wh = 16 mm. B–C. Ontogenetic development of striae distance (in mm) and striae distance/whorl height of specimen MB.C.30492 (Neben & Krueger Coll.) from Oderberg (Brandenburg). D–E. Ontogenetic development of striae distance (in mm) and striae distance/whorl height of specimen MB.C.30491 (Neben & Krueger Coll.) from Niederfinow (Brandenburg). F–G. Ontogenetic development of striae distance (in mm) and striae distance/whorl height of holotype MB.C.11730 (Kummerow Coll.) from Kranepuhl (Brandenburg). Blue dots = individual measurements, black lines = three data point averaged values. Scale bar units = 1 mm.