A new discosorid and some other nautiloids from the Givetian of the Rhenish Massif, Germany

Abstract

Nautiloids were subordinate inhabitants of Middle Devonian Rhenish reefs and in surrounding neritic carbonate facies. However, a literature review shows the presence of more than 45 orthoconic, cyrtobreviconic, and gyroconic taxa, which are mostly insufficiently known. We report the first discovery of an orthobreviconic representative of the order Discosorida from the initial phase (Binolen Member) of the thick Hagen-Balve Reef Complex in the Hönne Valley (northern Sauerland). It belongs to a new genus and species (Binoleniceras stichlingi n. gen. n. sp.) that is characterised by fast conch expansion, fine longitudinal ribbing, and a marginal siphuncle with short, recumbent cyrtochoanitic (dorsally) and suborthochoanitic (ventrally) septal necks, rounded adapical thickenings (bulletes), strongly thickened connecting rings, and irregular lamellae in the septal opening. It has no described relative in the Middle Devonian of Central or Southern Europe. Other taxa discussed are the oncoceratoid Cranoceras Hyatt, 1884, with the first Rhenish record of Cranoceras subdepressum (Roemer, 1850), and the archiacoceratid Cyrtoceratites, with a possibly new species with very large-sized siphuncle.