MARGINELLIFORM GASTROPODS FROM THE EARLY PLEISTOCENE OF GALLINA (REGGIO CALABRIA, SOUTHERN ITALY)

Marginelliforms are an informal group of marine gastropods including two families: Marginellidae Fleming, 1828 and Cystiscidae Stimpson, 1865. They are convergent families, mainly distributed in warm to warm-temperate waters, particularly difficult to be identified at species level, because of the their smooth, featureless shell. The present-day Mediterranean hosts a fairly diverse marginelliform fauna, but the genera with stronger tropical affinity, such as Marginella Lamarck, 1799, are missing since the Early-Middle Pliocene. Gallina is a fossiliferous locality on the Calabrian side of the Messina Strait. Its rich fossil fauna was studied by Seguenza (1879), who reported hundreds of species, mainly molluscs. He also remarked the unusual character of this “Astian” deposit as “facies misto”, as its rich assemblage consists of a mixture of shallow- and deep-water species. For this locality, Seguenza reported six species of marginelliforms. A small, poorly exposed outcrop, was recently discovered near Gallina. The outcrop contains a richly fossiliferous bed, 20 cm thick, consisting of clayey sands (level B), whose fauna corresponds to that studied by Seguenza. It overlays a clayey sandy bed with the Boreal Guest Pseudamussium septemradiatum (level A), and is overlaid by a poorly fossiliferous silty-sandy bed (level C). The nannoplankton assemblage from level A points to the large Gephyrocapsa Zone, while the assemblage from level C is indicative of the small Gephyrocapsa Zone (Early Pleistocene). The nannoplankton assemblage from the richly fossiliferous level B turned out to be totally reworked. All the three levels, particulalry the intermediate one (B), are interpreted as formed via gravitative flows. The marginelliform fauna from the “Seguenza level” (B) consists of some specie of the genus Granulina Jousseaume, 1888, two species of Gibberula Swainson, 1840 and one species of Marginella. One of these species corresponds to Marginella ovulaeformis Seguenza, 1879, described from Gallina. It seems a valid species, as Granulina ovulaeformis (Seguenza), but further studies are needed. The occurrence of a Marginella species at Gallina was quite unexpected, as none of the species reported by Seguenza can be actually referred to such a genus (widely used in the past literature). Furthermore, the species is relatively large (ca 10 mm in shell height) and fairly frequent in the assemblage. The abundant material (about 70 shells) is well preserved and reworking from older sediments is excluded. Most probably, it is an undescribed species, markedly different from the large sized M. aurisleporis (Brocchi, 1814), the last representative of Marginella in the Mediterranean Pliocene. It is worth remarking that several species of Marginella were reported from the Early-Middle Pliocene of Estepona, near the Gibraltar Strait (Landau et al., 2006). The Marginella species from Gallina testifies the local survival of this thermofilic genus through the Early Pleistocene in a Mediterranean “sanctuary”. Indeed, since the Pleistocene at least, the Messina Strait accommodates a high abundance and diversity of species, with many endemisms and primarily Atlantic species forming rich populations.