A New Miocene Deep-Sea Chiton and Early Evidence for Teredinidae-Sustained Wood-Fall Communities
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Palaeontologia Electronica palaeo-electronica.org A new Miocene deep-sea chiton and early evidence for Teredinidae-sustained wood-fall communities Luca Bertolaso, Vittorio Garilli, Daniela Parrinello, Maurizio Sosso, and Bruno Dell’Angelo ABSTRACT Deep-sea wood-falls are important biodiversity hot spots for insights on chemo- synthesis-based communities. The study of deep-sea wood-fall-related palaeocommu- nities from the Neogene of north Italy shed light on interesting associations from the Miocene of Torrente Cinghio (Tortonian) and of Moncasale di Casina (Langhian). The most common components of this association are typical chemosynthetic/wood-fall molluscs, such as the gastropods Homalopoma sp. and Pseudonina bellardii, the bivalves Idas sp. and shipworms, and the chiton Leptochiton lignatilis n. sp., which belongs to a genus typical of recent sunken woods in tropical waters. The new species described is compared with other fossil and recent congeners, especially with those sharing the same kind of tegmental sculpture, fully covered with randomly or quincun- cially arranged granules. An overview of the sunken wood-related chitons is provided. Surprisingly no taxa of the boring bivalves of the family Xylophagidae, whose species have been known to be fundamental for sustaining this kind of deep sea chemosyn- thetic ecosystem, were found in the studied site; however, other boring Teredinidae bivalves have been abundantly recovered. This suggests that, conversely to what has previously been observed on sunken wood communities, Teredinidae may be viewed as a counterpart for the maintenance of deep-sea wood-fall ecosystems. Luca Bertolaso. Via Manzotti 35, 42015 Correggio (RE), Italy. [email protected] Vittorio Garilli (corresponding author). Paleosofia - APEMA Research & Educational Service, Via Alla Falconara, 34, 90136 Palermo, Italy. [email protected] Daniela Parrinello. Department of Biological, Chemical and Pharmaceutical Science and Technology, “Animal Biology Section”, University of Palermo, Via Archirafi 18, 90100 Palermo, Italy. [email protected] Maurizio Sosso. Via Bengasi 4, 16153, Genova, Italy. [email protected] Bruno Dell’Angelo. Museo di Zoologia, Via Selmi 3, 40126 Bologna, Italy. [email protected] Keywords: wood-fall; Polyplacophora; new species; Teredinidae boring bivalves; Miocene; Mediterranean area Submission: 21 March 2015. Acceptance: 9 July 2015 http://zoobank.org/17950F77-D49D-4D22-A0FD-77240FD36070 Bertolaso, Luca, Garilli, Vittorio, Parrinello, Daniela, Sosso, Maurizio, and Dell’Angelo, Bruno. 2015. A new Miocene deep-sea chiton and early evidence for Teredinidae-sustained wood-fall communities. Palaeontologia Electronica 18.2.41A: 1-15 palaeo-electronica.org/content/2015/1277-miocene-wood-fall-community Copyright: Palaeontological Association August 2015 BERTOLASO, ET AL.: MIOCENE WOOD-FALL COMMUNITY INTRODUCTION 1971; McKoy, 1980; Pailleret et al., 2007; Saito, 2013; Voight, 2015 with other references therein), Large nekton and wood-falls are important but it is still not clear how long they can survive at local resources of organic carbon in otherwise oli- such depths or, at least, whether “the considerable gotropic deep-sea environments. Recently an artifi- time they may survive” (Turner, 1968) is enough for cial deployment of a wood-fall in the Central Nile maintaining a chemosynthetic ecosystem. Evi- deep-sea fan delta in the Eastern Mediterranean dence is likewise lacking for the possibility of tered- (Bienhold et al., 2013) showed that, after only one inid larval colonization of deep-water wood-falls year, the presence of wood on the seafloor led to (Turner, 1968), because it has so far only been the creation of lower oxygen and sulfidic condi- detected at shallow depths, from 7.6-25.9 m tions, prerequisites for colonization by specialized (Edmonson, 1962) to 60.9 m (Haderlie and Mellor, and/or opportunistic wood-fall fauna. As suggested 1973), with increased settlement of some species by Distel et al. (2000), whale falls, wood-falls and at greater depths (Quayle, 1992 and references other organic falls may provide important steps for therein). Wood deployed on a 183-267 m deep bot- the introduction of recent benthos to vents and tom near the Bahamas, however, was recovered seeps biota. Kaim et al. (2008) achieved similar with two teredinid species (Heise et al., 2011). conclusions for the fossil record, postulating the Apart from the boring bivalves, other special- role of Mesozoic marine reptile carcasses as evo- ized, opportunistic molluscs may colonize sunken lutionary and dispersal stepping stones. Moreover, wood on deep bottoms, whereas colonizers at studies by McClain and Barry (2014) on woods shallow sites are unspecialized species that are deployed on deep-sea bottoms have provided con- normally present in the background fauna (Santha- vincing estimates of how wood-fall environments kumaram and Sneli, 1984; Berg et al., 1987). For may contribute to biodiversity. example, several taxa in the class Polyplacophora Many observations on naturally sunken and Gray, 1821 (i.e., chitons), particularly in Lepido- deployed woods (e.g., Bernardino et al., 2010; pleurida Thiele, 1909, may colonize sunken wood Samadi et al., 2010; Heise et al., 2011) have high- in deep waters. Chitons are closely related to, and lighted the importance of factors such as wood in some cases specialized for, this kind of substrate type and size, position on wood logs, time after especially in tropical waters. Documentation of chi- deployment, water temperature and depth in influ- tons in the fossil record that are related to wood-fall encing the pattern of wood colonization, a situation ecosystems are generally rare, however, thus mak- analogous to that evidenced for whale falls (e.g., ing the origin of their possible specialization on Lundsten et al., 2010). wooden substrates, as well their phylogenetic rela- The wood-boring bivalves of the family Xylo- tionship, a matter of debate. phagidae Purchon, 1941 are the main colonizers of Here we describe the first results of taxonomic naturally and artificially sunken woods in deep and palaeoecological analyses of the invertebrate water, usually in 400-3203 m (Turner, 2002; Voight, assemblages from some Italian Neogene deposits 2007, 2015). These bivalves have an important along the foothills of the northern Apennine Moun- role in the initial degradation of the wood, as they tains, with special regard to molluscs from organic- transform the energy accumulated in the wood tis- rich marine palaeoenvironments. Specifically the sue into nutrients that are available for other ani- goals of this work are to characterize the main mol- mals (Turner, 1973, 1978). This transformation is luscan species recovered from a wood-fall associa- accomplished by both the decomposition of woody tion, which is the first described Italian Miocene material and the contribution of faecal pellets and wood-fall deposit, and to provide larval stages that rain down to the sediment sur- preliminarily discussion of the role of boring Tered- face (Bernardino et al., 2010), setting up the best inidae bivalves in the trophic structure of a deep- conditions for bacterial exploitation and for activat- sea wood-fall community. Our report also ing a chemosynthesis-based chain. The develop- includes the description of a new species of the ment of a chemically reducing habitat allows for the chiton genus Leptochiton Gray, 1847. colonization of taxa capable of sustaining elevated concentrations of sulfide. Geological Setting and Stratigraphy of the The drifting/floating wood may, however, be Study Sites colonized by bivalves of the family Teredinidae The study sites are located in the domains Rafinesque, 1815. Some of these bivalves have resulting from a compressional tectonic regime, been found alive in sunken wood retrieved from the between the Adriatic-Apulian foreland structural deep sea (Turner, 1968; Nair and Saraswathy, 2 PALAEO-ELECTRONICA.ORG 6° E 10° E 1 Molasse Basin 1 3 2 46° N Emilia-Romagna Po Basin Adriati N Italy o*rt c foreland he rn 44° N A p en n in e s 250 km Foreland area Alpine thrusting N Foredeep deposits Area with extensional tectonics Domains with Apennine compression Main thrusts 2 * 3 Moncasale * Torrente Cinghio Casatico 44°39’03’’N 44°31’19’’N Casalio 500 m 10°15’36’’E 500 m 10°30’24’’E Continental deposits, Quaternary Cigarello Formation, early Serravallian Lugagnano clays, Pliocene Pantano Formation, late Burdigalian-early Langhian Colombacci Formation, Messinian Contignaco Formation, Aquitanian-early Burdigalian Termina Formation, Tortonian Undifferentiated Palaeogene (Lutetian-late Rupelian) FIGURE 1. Location of the study area and of the Torrente Cinghio and Moncasale sites (asterisks) in the structural map (1) of northern Italy (modified from Scrocca et al., 2003) and in their respective geological setting (2-3) as modi- fied from Papani (2002) and Di Dio and Zanzucchi (2005). domain and the main thrust of the Northern Apen- Emilia, N Italy), in a gully situated on the left side of nines (Figure 1.1), a rapidly migrating thrust belt the “Fosso di Moncasale” (Figure 1.3). The lower developed mainly in Neogene times during the and middle parts of the exposure belong to the eastward roll-back of the subducting Adriatic plate Pantano Fm, aged late Burdigalian - Langhian (Scrocca et al., 2003). (Amorosi et al., 1993). This material comes from Most of the studied material comes from the sediment that contains Praeorbulina glomerosa cir- sediments of