Rhynchorthoceras beyrichii Remele 1882
| Main Authors: | Aubrechtová, Martina, Korn, Dieter |
|---|---|
| Format: | info publication-taxonomictreatment Journal |
| Terbitan: |
, 2022
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/6347598 |
Daftar Isi:
- Rhynchorthoceras beyrichii Remelé, 1882 Fig. 14D, Tables 2–3 Rhynchorthoceras Beyrichii Remelé, 1882: 128, pl. 5 fig. 3a–b. Orthoceratites – Breyn 1732: 33, pl. 4 figs 1–3. Ancistroceras Breynii – Remelé 1881: 194. Rhynchorthoceras beyrichi – Foerste 1930: 277, pl. 42 fig. 2a–c. — Balashov 1962: pl. 7 fig. 3. Diagnosis Species of the genus Rhynchorthoceras with an expansion angle of 15–17°. Shell surface with pronounced lirae, straight in the apical part but faintly sinuous later in ontogeny. Distance of lirae increasing up to 1.5 mm during ontogeny; distance and thickness of lirae might be irregular. Siphuncle eccentric in position (after Remelé 1882). Type material Not available for study; Remelé (1882: pl. 5 fig. 3a–b) did not specify a type, but he mentioned and illustrated only one specimen from Szczecin (formerly Stettin; West Pomerania, Poland), found in Upper Grey Orthoceratite Limestone erratics in Pleistocene gravel (late Darriwilian, Middle Ordovician). Material examined POLAND • 1 spec.; Osselsk; Ordovician; Henke 1901 Coll.; MB.C.11718. Description Specimen MB.C.11718 (Fig. 14D) is a 50 mm long fragment of an orthoconic phragmocone; it is sectioned along the median plane (a thin section was also produced by a previous researcher). The conch expands with an expansion angle of 17°. The ornament consists of flat, asymmetric lirae (the steeper side facing the aperture), which form a shallow lateral sinus and a low dorsal projection. The shell wall is not preserved on the ventral side. During ontogeny, the siphuncle shifts slightly in position (from 0.40–0.45); it has a diameter of 0.15 of the whorl height. The connecting rings are slightly expanded in their first half. The chamber length is stable (CLR = 0.25–0.27). Remarks Rhynchorthoceras beyrichii is distinguished from the other species of the genus by the moderately high expansion angle (15°–17°) and an ornament with sinuous lirae. The lirae are much less sinuous and narrower than in the otherwise similar R. breynii (from Middle Ordovician erratics of northern Germany) and R. zaddachi (Remelé, 1882) (from Darriwilian erratics of the Kaliningrad Region, Russia). Rhynchorthoceras beyrichii is a rare species that is unequivocally known only from two specimens figured by Remelé (1882) and Foerste (1930); the latter specimen was available for study herein. Dzik (1984) figured a specimen of Rhynchorthoceras from Volkhovian (early Middle Ordovician) strata of Poland that he assigned to R. aff. beyrichi. Geographic and stratigraphic occurrence Poland (in erratics within Pleistocene gravels); Upper Grey Orthoceratite Limestone, late Lasnamägi Regional Stage (late Darriwilian, Middle Ordovician).
- Published as part of Aubrechtová, Martina & Korn, Dieter, 2022, Taxonomy and ontogeny of the Lituitida (Cephalopoda) from Orthoceratite Limestone erratics (Middle Ordovician), pp. 1-108 in European Journal of Taxonomy 799 (1) on pages 21-24, DOI: 10.5852/ejt.2022.799.1681, http://zenodo.org/record/6341270