Rineceras Hyatt, 1893

Korn, Dieter & Bockwinkel, Jürgen, 2022, Early Carboniferous nautiloids from the Central Sahara, southern Algeria, European Journal of Taxonomy 831, pp. 67-108 : 71-72

Genus Rineceras Hyatt, 1893

Type species

Gyroceras propinquum de Koninck, 1880 ; subsequent designation by Foord (1900).

Diagnosis

Genus of the family Trigonoceratidae with evolute conch; whorls detached or slightly in contact; whorl profile elliptical or rounded-triangular with broad venter. Ornament with coarse growth lines and fine or coarse spiral lines; coarse granulation at the crossing points of growth lines and spiral ridges. Suture line with shallow external and lateral lobes. Siphuncle small with subcentral position (after Kummel 1964; emended by Korn et al. 2022).

Included Early Carboniferous species

Rhineceras alapaevskensis Kruglov, 1934 , Urals; Pararineceras balladoolense Turner, 1954 , Isle of Man; Nautilus canaliculatus von Eichwald, 1857 , South Urals; Rineceras carinatiforme Shimansky, 1967 , Kazakhstan; Nautilus carinatus von Eichwald, 1857 , Western Russia; Nautilus (Discus) digonus Meek & Worthen, 1860 , Indiana; Nautilus Luidii Fleming, 1828 , Derbyshire; Gyroceras Meyerianum de Koninck, 1844 , Belgium; Rineceras multituberculatum Korn, Miao & Bockwinkel, 2022 , Algeria; Rineceras ohioense Miller & Garner, 1953 , Ohio; Triboloceras patteiskyi Schmidt, 1951 , Rhenish Mountains; Gyroceras propinquum de Koninck, 1880 , Belgium; Rineceras rectangulatum Korn, Miao & Bockwinkel, 2022 , Algeria; Nautilus rhenanus Holzapfel, 1889 , Rhenish Mountains; Rineceras tenerum sp. nov., Algeria.

Remarks

Due to differing opinions on the significance of the general shape of the conch, there is disagreement on the species spectrum of the genus Rineceras . Turner (1953) revised the species originally described by Martin (1793, 1809) as “Conchyliolithus N. Ammonites (Luidii)”, and subsequently, he introduced the genus Pararineceras on the basis of this species ( Turner 1954). This species differs from the type species of Rineceras only by the more densely coiled conch and the supposed “straightening out in late maturity”. The first of these two characters might be gradual and not useful for a separation of genera and the second cannot really be demonstrated in the holotype, which has a conch diameter of only 28 mm.

Kummel (1964) accepted both genera without providing clear distinguishing characters, but Shimansky (1967) and Dzik (1984) regarded Pararineceras as a synonym of Rineceras . In the following, we treat Pararineceras as a junior synonym of Rineceras until a clear separation can be demonstrated.

Rineceras is restricted here to those species that have a whorl profile with a rounded outline. This means that the species Nautilus (Trematodiscus) Meekianus Winchell, 1862 and Nautilus (Trematodiscus) strigatus Winchell, 1862 , both with longitudinal grooves on the venter, placed in Rineceras by Miller & Garner (1953), are excluded from Rineceras and listed in the new genus Stroborineceras gen. nov.

Rineceras belongs to the ancestral Early Carboniferous genera in the evolution of the nautilid family Trigonoceratidae . This is supported not only by the early stratigraphic occurrence in strata of the early late Tournaisian, but also by the morphology with a rather simple overall whorl profile without the longitudinal grooves and ridges often present in many derived forms, which there lead to a more complex geometry.