Journal of Paleontology, 91(3), 2017, p. 444–466 Copyright © 2017, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2016.154
Chemosymbiotic bivalves from Miocene methane-seep carbonates in Italy
Steffen Kiel,1 and Marco Taviani2,3,4 1Swedish Museum of Natural History, Department of Palaeobiology, Box 500 07 104 05 Stockholm, Sweden ⟨
steffen.kiel@
nrm.se⟩ 2Institute of Marine Sciences, Italian National Research Council, Via Gobetti 101, 40129 Bologna, Italy 3Biology Department, Woods Hole Oceanographic Institution, 266Woods Hole Rd,Woods Hole,MA 02543, USA ⟨
marco.taviani@bo.ismar.cnr.it⟩ 4Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Naples, Italy
Abstract.—Eleven species of chemosymbiotic bivalves are reported from middle to late Miocene methane seep deposits (‘Calcari a Lucina’) in the Italian Apennines, including seven new species and one new genus. The new species are Bathymodiolus (s.l.) moroniae and B.(s.l.) miomediterraneus among the Bathymodiolinae and Archivesica aharoni, A. apenninica, A. strigarum,and ‘Pliocardia’ italica among the Vesicomyidae; specimens from the middle Miocene of Deruta are reported as Archivesica aff. aharoni. Samiolus iohannesbaptistae new genus new species is introduced for an unusual mytilid with a commarginally ribbed surface, which might be the first non-bathymodiolin mytilid obligate to the seep environment. The two large lucinid species from which these deposits derived their informal name ‘Calcari a Lucina’ are identified as Meganodontia hoernea (Des Moulins, 1868) and Lucinoma perusina (Sacco, 1901). With Chanellaxinus sp., we report the first thyasirid from a Neogene deep-water seep deposit in Italy and the first fossil occurrence of this genus.
Introduction
Limestone deposits yielding large lucinid bivalves have been known for centuries from the Miocene deposits in Italy, and were termed ‘Calcari a Lucina’ (Manzoni, 1876; Coppi, 1877; Scarabelli, 1880; Sacco, 1901; Di Stefano, 1903). Due to their isolated occurrence in deep-water sediments and the large bivalves preserved in them, they were considered to have been transported from shallow water (Ricci Lucchi and Veggiani, 1967). This view changed after the first discovery of faunal communities at methane seeps in the deep Gulf of Mexico with similarly large bivalves (Paull et al., 1984) and the recognition that methane seep carbonates can be identified based on their distinctive, light carbon isotope signature (Hovland et al., 1987). The ‘Calcari a Lucina’ deposits throughout Italy are nowconsidered as ancient deep-water methane seep deposits (Clari et al., 1988; Conti et al., 1993; Terzi, 1993;Aharon and SenGupta, 1994; Berti et al., 1994; RicciLucchi and Vai, 1994; Taviani, 1994; Terzi et al., 1994; Peckmann et al., 1999; Clari et al., 2004b; Conti et al., 2004, 2010). Despite this wealth of geologic literature on these deposits, modern studies on the macrofauna are relatively rare (Moroni, 1966; Taviani, 1994, 2011, 2014; Taviani et al., 2011). The purpose of the present contribution is to provide a revision of the major taxa of chemosymbiotic bivalves of the ‘Calcari a Lucina’ deposits, with exclusion of solemyids.
Materials and methods
Specimenswere coatedwith ammoniumchloride for photography. The material is from twelve seep deposits of middle to late Miocene age (Fig. 1) associated with deep-water hemipelagic marls or turbidites, mostly ascribed to the Marnoso-arenacea
Formation. Their geological and stratigraphic context is described in various publications (Vai et al., 1997; Conti and Fontana, 1999; Clari et al., 2004b; Taviani, 2011). A short description of the localities is provided in the Appendix.
Repositories and institutional abbreviations.—MGGC: Museo Geologico Giovanni Capellini, University of Bologna; MSF: Museo Civico di Scienze Naturali, Faenza; MZB: Museo dell’Evoluzione (formerly Zoologia), University of Bologna; MRSN: Museo Regionale di Scienze Naturali, Torino (managing the Bellardi and Sacco collection, property of the Turin University).
Systematic paleontology Class Bivalvia Linnaeus, 1758
Subclass Pteriomorphia Beurlen, 1944 Order Mytilida Férussac, 1822 Family Mytilidae Rafinesque, 1815
Genus Bathymodiolus Kenk and Wilson, 1985
Type species.—Bathymodiolus thermophilus Kenk and Wilson, 1985, Recent, Galapagos Rift Zone, by original designation.
Remarks.—Molecular phylogenetic studies have shown that species currently classified as Bathymodiolus belong to at least two clades within the bathymodiolins (Gustafson et al., 1998; Jones et al., 2006; Lorion et al., 2010, 2013; Thubaut et al., 2013), of which those related to B. childressi may be placed in a separate genus. This species group is often referred to as the ‘childressi clade’ and it is recommended to use “Bathymodiolus” only in quotationmarks for these species until the taxonomic uncertainties
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