First record of the enigmatic coleoid genus Longibelus from Sakhalin (Far East Russia): a contribution to our understanding of Cretaceous coleoid habitats in the Pacific Realm

Abstract

A newly collected specimen of the enigmatic coleoid genus Longibelus is recorded from lower Turonian strata along the River Shadrinka in Sakhalin (Russian Far East). To date, this is the first record of Late Cretaceous coleoid cephalopods from the island and, in fact, from the entire Pacific coast of the Russian Federation. Lithological characteristics, coupled with published geochemical analyses (δ13C and Corg content), suggest the habitat of this coleoid taxon to have been the middle to outer (i.e. distal) shelf. Its provenance from the stratigraphical level that is known as the Scaphites Event, characterised by a mass occurrence of Scaphites and Yesoites, may be indicative of occasional or marginal overlap in ranges, rather than life in similar habitats. On the basis of lithological features and in view of the extremely rare occurrence of Longibelus in rich ammonite assemblages with clear ecological/bathymetric preferences, the natural habitat of Longibelus may have comprised neritic to mesopelagic zones over distal shelves and slopes.