Rhynchorthoceras Remelé, 1882

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 : 12-13

Genus Rhynchorthoceras Remelé, 1882

Type species

Lituites Breynii Boll, 1857 ; subsequent designation by Furnish & Glenister (1964).

Diagnosis

Genus of the family Sinoceratidae with orthoconic, longiconic conch, slightly curved in the apical part; expansion angle between 8° and 17°; whorl profile circular or compressed. Shell surface smooth or decorated with transverse lirae or striae. Siphuncle ca 15% of whorl height, central or subcentral in position, displaced towards the convex side of the conch; septal necks orthochoanitic, connecting rings tubular or slightly expanded within chambers. Cameral deposits with single vertical lamellae on the concave side of the conch (after Kröger et al. 2007, emended).

Species included

Lituites angelini Boll, 1857 ; Rhynchorthoceras Beyrichii Remelé, 1882 ; Lituites Breynii Boll, 1857 ; Rhynchorthoceras blackduckense Stait, 1988 ; Rhynchorthoceras concavum Lai & Wang, 1986 ; Orthoceratites conicus Hisinger, 1837 ; Cyrtoceras damesi Dewitz, 1879 ; Rhynchorthoceras guanyinqiaoense Lai, 1986 ; Rhynchorthoceras helgoeyense Sweet, 1958 ; Rhynchorthoceras jurongense Zou, 1988 ; Rhynchorthoceras kranepuhlense sp. nov.; Rhynchorthoceras lineatum Lai, 1987 ; Rhynchorthoceras lunshanense Zou, 1988 ; Rhynchorthoceras minor Kröger et al., 2007 ; Rhynchorthoceras paucisinum Lai, 1987 ; Rhynchorthoceras rugium sp. nov.; Rhynchorthoceras yizanense Fang et al., 2021 ; Rhynchorthoceras Zaddachi Remelé, 1882 ; Rhynchorthoceras zhejiangense Zou, 1987 .

Geographic and stratigraphic occurrence

Argentine Precordillera, Canada, Baltoscandia, Wales (?), northern Germany, Poland, the Kaliningrad Region of Russia, northern Poland, Bohemia and China; Middle to Late Ordovician.

Remarks

Rhynchorthoceras includes the stratigraphically oldest, Dapingian, lituitid species ( Kröger et al. 2007; Aubrechtová & Turek 2018; Fang et al. 2021).

Species of Rhynchorthoceras differ from the species of Sinoceras by a greater expansion angle and shorter septal necks, and from the species of Tyrioceras in shorter phragmocone chambers. Fang et al. (2021) suggested to synonymise Tyrioceras with Rhynchorthoceras , but the collection studied here is not sufficient to address this issue.

Species of Ancistroceras and Holmiceras of the family Lituitidae differ from the species of Rhynchorthoceras in the coiled juvenile conch. Also, the conchs in the species of Ancistroceras and Holmiceras usually expand more strongly and are more prominently ornamented (with annuli). However, some species of the three genera might be difficult to separate, if apical portions of the conchs are missing ( Kröger et al. 2007; Aubrechtová & Meidla 2020; Fang et al. 2021).