Descubren un nuevo género de molusco en el Toarciense de la Península Ibérica

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

Resumen : Historically, most of the nautiloids arisen during the Early Jurassic have been assigned initially to the genus Nautilus LINNAEUS, 1758, and subsequently to Cenoceras HYATT, 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 fourneti DUMORTIER, 1874 (selected as type species), Nautilus inornatus d'ORBIGNY, 1843, Nautilus anomphalus PIA, 1914, Nautilus jurensis QUENSTEDT, 1846-49, and, with doubts. Cenoceras globulus RULLEAU, 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.

Autores : Fernando Barroso-Barcenilla, Maria Jose Comas-Rengifo, Luis Vitor Duarte, Antonio Goy, Gemma Martinez.

Direcciones :
1. Univ Complutense Madrid, Fac Ciencias Geol, Dept Paleontol, E-28040 Madrid, Espana, Spain
2. Univ Alcala de Henares, Grp Invest IBERCRETA, Alcala De Henares 28871, Espana, Spain
3. Univ Coimbra, Fac Ciencias & Tecnol, Dept Ciencias Terra IMAR CMA, P-3000272 Coimbra, Portugal