A new genus of nautiloid in the Toarcian of the Iberian peninsula (Spain and Portugal)

• DOI: 10.2113/gssgfbull.182.5.391
• Publication Date: 2011-11-01T23:48:54Z
• Authors: Fernando Barroso-...; María José Coma...; Luís Vítor Duarte; Antonio Goy; Gemma Martínez
• Keywords: Portugal; Nouveau genre; Espagne; 594.52"622.428"(46); Nautiloidea; Toarcien; Toarcian; Jurassique inférieur; 2416.02 Paleontología de Los Invertebrados; Iberian peninsula; Péninsule ibérique; 01 natural sciences; Paleontología; Lower Jurassic; Spain; New genus; 0105 earth and related environmental sciences

Abstract Historically, most of the nautiloids arisen during the Early Jurassic have been assigned initially to the genus NautilusLinnaeus, 1758, and subsequently to CenocerasHyatt, 1884. At present, a tendency to rehabilitate other genera or to describe new ones predominates among the few authors who try to classify and to group these problematic cephalopods. In the present work, the new genus Ligeiceras has been described for remarkably small and involute nautiloids with notably retrogressive suture lines. It has a smooth or slightly ornamented external surface, limited to thin tenuous, ventraly retroverse and distant growth lines and longitudinal and transversal striae. This group, seemingly, appeared after the biotic crisis of the end of the Tenuicostatum/Polymorphum Zone, evolved during the radiation of the Early Toarcian Serpentinum/Levisoni Zone and the Late Toarcian, and survived at least until the Aalenian. New specimens from the Iberian peninsula (Basque-Cantabrian and Iberian basins, Spain; and Lusitanian basin, Portugal), belonging to the taxa Nautilus fournetiDumortier, 1874 (selected as type species), Nautilus inornatusd’Orbigny, 1843, Nautilus anomphalusPia, 1914, Nautilus jurensisQuenstedt, 1846-49, and, with doubts, Cenoceras globulusRulleau, 2008, have been collected, described and assigned to this systematic group. Although some of these species have already been cited in the literature, Ligeiceras fourneti, Ligeiceras jurensis and Ligeiceras? globulus have never been previously clearly described or illustrated, and their stratigraphic distribution has not been determined accurately for the Iberian peninsula, as has been done here for these taxa and for Ligeiceras inornatus and Ligeiceras anomphalus. Therefore, the present work on the new genus Ligeiceras constitutes a notable advance in the knowledge of these nautiloids, and seems to confirm that the dwarfism could have been a relatively generalized tendency in the Upper Toarcian of southwestern Europe, possibly due to palaeoenvironmental causes.