Revision of the pragian Rutoceratoidea Hyatt, 1884 (Nautiloidea, Oncocerida) from the Prague Basin

Abstract

Superfamily Rutoceratoidea Hyatt, 1884 (Pragian to Frasnian, Devonian) includes nautiloid cephalopods having exogastric cyrtoceracone or coiled shells with periodic walls or raised growth lines (megastriae) forming ridges, sometimes modified in various ways into collars, frills, or different outgrowths. High disparity and intraspecific variability of the shell form and sculpture of the rutoceratoids are conspicuous among Early Palaeozoic nautiloids. Consequently, rutoceratoids are divided according to different patterns of growth structures into three families. Parauloceratidae fam. nov. (Pragian to Emsian) contains taxa with cyrtoceracone shells and simple recurrent ribs with ventral sinus. Family Hercoceratidae Hyatt, 1884 (Pragian to Givetian) comprises forms with periodically raised ridges with three lobes forming ventrolateral outgrowths during shell growth such as wings, nodes or spines. Family Rutoceratidae Hyatt, 1884 (Pragian to Frasnian) encompases taxa having growth ridges with ventral lobe transforming into undulated frills or distinct periodic collars (megastriae). All of these families had already appeared during early radiation of rutoceratoids in the Pragian. The early radiation of rutoceratoids is, however, adequately recorded only from the Prague Basin. Rutoceratoids become widespread within faunas of Old World and Eastern American realms later during the Emsian and especially Middle Devonian. Three new genera are erected: Parauloceras gen. nov., Otomaroceras gen. nov. and Pseudorutoceras gen. nov. The Pragian Gyroceras annulatum Barrande, 1865 is assigned to the genus Aphyctoceras Zhuravleva, 1974. Rutoceratoids are thus represented by seven genera and eight species in the Pragian Stage of the Prague Basin. In addition, variability of shell coiling among rutoceratoids and its significance for their systematics are discussed.