Gzhelian–Asselian) of Guardia Pisano (Sardinia, Italy
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New hybondontoid shark from the Permocarboniferous (Gzhelian–Asselian) of Guardia Pisano (Sardinia, Italy) JAN FISCHER, JÖRG W. SCHNEIDER, and AUSONIO RONCHI Fischer, J., Schneider, J.W., and Ronchi, A. 2010. New hybondontoid shark from the Permocarboniferous (Gzhelian– Asselian) of Guardia Pisano (Sardinia, Italy). Acta Palaeontologica Polonica 55 (2): 241–264. Numerous isolated teeth, fin spine fragments and dermal denticles of a hybodont shark from a lacustrine limestone hori− zon at the top of lithofacies B of the Late Carboniferous to Early Permian succession of the Guardia Pisano Basin (Sulcis area, southwestern Sardinia, Italy) are assigned to a new species of the genus Lissodus Brough, 1935. Lissodus sardiniensis sp. nov. is erected on the basis of about 500 teeth, which show a unique feature of only one pair of lateral cusps that are bent in the direction of the prominent central cusp. Weak heterodonty allows distinction of symphyseal, mesial to anterolateral, and lateral teeth. Lissodus sardiniensis sp. nov. was a freshwater−adapted durophagous shark of bottom dwelling habit, an interpretation supported by general construction of the dentition and the morphology of the der− mal denticles. The association with Acanthodes, diplodoselachid sharks and branchiosaurs allows the reconstruction of a five−level trophic chain for the Guardia Pisano Basin. The discovery of Lissodus in Sardinia is presently the southernmost known occurrence of that genus in the Late Palaeozoic of Europe. This new find adds significantly to knowledge of mi− gration routes of aquatic organisms, especially freshwater sharks, between the single European basins in the Late Penn− sylvanian, and changes in palaeobiogeography during the Early Permian. Key words: Chondrichthyes, Hybodontoidea, Lissodus, taxonomy, palaeoecology, palaeobiogeography, Sardinia, Italy. Jan Fischer [[email protected]] and Jörg W. Schneider [[email protected]−freiberg.de], Department of Palaeontol− ogy, Geological Institute, Technische Universität Bergakademie Freiberg, Bernhard−von−Cotta Straße 2, 09599 Frei− berg, Germany; Ausonio Ronchi [[email protected]], Dipartimento di Scienze della Terra, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy. Received 30 January 2009, accepted 22 October 2009, available online 11 January 2010. Introduction ments, > 150 dermal denticles and numerous fin spine frag− ments from only a small limestone sample of about 1 kg. Isolated remains of the chondrichthyan hybodontoid genus Institutional abbreviation.—FG, Geological Institute, Tech− Lissodus are known so far from the European non−marine Late nical University Bergakademie Freiberg, Germany. Carboniferous to Early Permian of Spain, France, Germany, Czech Republic, and Ukraine (Gebhardt 1988; Soler−Gijón Other abbreviations.—LAD, last appearance datum; LOD, 1993; Soler−Gijón 1997; Steyer et al. 2000; Zajíc 2000; Duffin last occurrence datum; NM, find locality Niedermoschel, 2001). The first record of Lissodus from the Guardia Pisano Germany; SCE, single crystallite enameloid. Basin (Sulcis) in SW Sardinia (Fig. 1) was reported by Freytet et al. (2002), and subsequently mentioned by Schneider et al. (2003) and Fischer et al. (2003). Intensified micropalaeonto− logical processing of limestone boulders, sampled by J.S. dur− Geological and stratigraphical ing a field trip of the Brescia Symposium in 1999, has pro− setting vided an extremely fossiliferous and diverse assemblage of isolated fish remains (Fischer 2005) as well as indeterminable The Guardia Pisano Basin was a small intramontane trough branchiosaur−like jaw fragments (Werneburg et al. 2007). The located in the Sulcis area of SW Sardinia, Italy (Fig. 1), close fish assemblage is dominated by teeth, dermal denticles and to the village of Gonnesa (Barca et al. 1992; Pittau et al. fin spine fragments of a previously unknown species of Lisso− 1999). Today, what remains of this basin is only an about 130 dus, and scales and fin spine fragments of Acanthodes sp. metre−thick continental volcano−sedimentary succession The material described below is exceptional because of (Pittau et al. 2002; Barca and Costamagna 2006; Ronchi et al. the large number (> 500) of isolated teeth and tooth frag− 2008), which crops out on the road to Portoscuso. The depos− Acta Palaeontol. Pol. 55 (2): 241–264, 2010 doi:10.4202/app.2009.0019 242 ACTA PALAEONTOLOGICA POLONICA 55 (2), 2010 its are generally divided into four informal lithostratigraphic 9° units, separated by facies changes or unconformable strati− graphic contacts and covered by Eocene marine limestones (Fig. 2). The lower section comprises two units (Pittau et al. 1999): lithofacies A (Fig. 2), 6–7 m (base not exposed) 41° of dark grey carbonaceous shales with sporadic sandstone lenses; and lithofacies B (Fig. 2), about 15 m of alternating carbon−rich shales, sandy dolostones, tuffs and brecciated rhyolitic and rhyodacitic lavas. Following an erosional un− conformity, lithofacies C (Fig. 2) of the upper section fol− lows with about 45 m of medium–fine−grained reddish sand− stones and micaceous siltstones with interstratified conglom− erate layers and dark shale lenses. This is unconformably overlain by lithofacies D (Fig. 2) with 60–70 m of pur− plish−red sandstones and pelites with repeatedly intercalated pebbly fine sandstones and conglomerates. The depositional environment associated with volcanic ac− tivity shifts from blackish−grey sediments of a predominantly palustrine and fluvio−lacustrine system (lithofacies A, B) to grey and reddish sediments of a fluvial (C) to an alluvial plain 40° system (D) under a hot and humid climate (Pittau et al. 1999, 2002; Barca and Costamagna 2006; Ronchi et al. 2008). The lower unit yields a macroflora of pecopterid and coni− Perdasdefogu fer remains. Furthermore, lithofacies A has provided a micro− Basin floral assemblage (21 spore and 23 pollen genera, Pittau et al. 1999, 2002) in a very good state of preservation, indicating a Guardia meso− to xerophilic flora, which grew in a dry environment Pisano at tropical−subtropical latitudes. This palynological association Basin allows a biostratigraphic comparison with the Gzhelian–As− selian of the Donetsk and Ural basins, the Early Wolfcampian (Asselian) of the North American Midcontinent and the Stephanian–Autunian (Gzhelian–Asselian) transition of West− ern Europe (Pittau et al. 1999). Radiometric determinations (SHRIMP and lead−zircon evaporation method) on the interca− lated calcalkaline volcanic rocks of lithofacies B delivered a date of 297 ± 5 Ma (Pittau et al. 2002) that is in good agreement 39° with palynological data. For the upper unit only an imprecise 02550kmpost−Asselian age can be assumed because of the absence of time−indicative fossils (Pittau et al. 2002; Ronchi et al. 2008). Variscan The isolated vertebrate remains reported here were ex− batholith tracted from an 80–90 mm thick brownish−grey lacustrine high to low grade micritic limestone, which covers a black pelite in the upper metamorphic complex part of lithofacies B (Fig. 2) with an erosive junction. From the Adriatic Sea main fault bottom to the top of the bed a transition from a peloidal micrite Mesozoic and about 15 mm thick into a fine sandy siliciclastic micrite is ob− Italy Corsica N Cenozoic cover served with a concomitant increase in larger clasts from 2 to Permian and Triassic 10%. The peloids have a diameter of 0.2–2 mm, and associ− continental deposits ated cellular plant fragments (?wood particles) have a size Sardinia and volcanic complexes range of 1–5 mm. The siliciclastic components are clay, silt Tyrrhenian Sea and fine sand particles. The larger clasts consist of grey to beige, rounded limestone intraclasts of 1–5 mm diameter and Sicily 2–4 mm large charcoal particles. Pieces of twig−like petrified 0 100 200 km wood in the upper part of the limestone reach 20 mm in diame− ter. Aquatic invertebrates, ostracods and small (3 mm−long) Fig. 1. Geological map of Sardinia with the locations of the Guardia Pisano gastropods, are rare. The C−org rich black pelite below the and Perdasdefogu basins (modified from Werneburg et al. 2007). limestone contains isolated vertebrate remains in much higher FISCHER ET AL.—NEW HYBONDONTOID SHARK FROM SARDINIA 243 siltstone Serie Systematic palaeontology and shales lignitifera Auct coarse-to-fine Eocene sandstones The fossil record of Lissodus shows a widespread modern conglomerates stratigraphic gap geographical distribution from Europe (Schneider et al. and breccias volcaniclastic 2000; Steyer et al. 2000; Duffin 2001; Duncan 2004), Asia deposits (Chang and Miao 2004; Prasad et al. 2004; Rees and Under− dolostones wood 2006, Prasad et al. 2008), Australia (Trinajstic and limestones and George 2007; Susan Turner, personal communication 2008), lithofacies clay-sandy North America (Zidek et al. 2004; Hunt et al. 2006; Milner limestones D and Kirkland 2006) and Africa (Brough 1935; Antunes et al. (60–70 m) tuff 1990; López−Arbarello 2004). The stratigraphic record com− fish teeth prises about 300 million years from the Late Devonian (Fras− and remains nian) to the Late Cretaceous (Maastrichtian) (Duffin 2001; macro Fischer 2008). Although Lissodus is found in rocks of marine and microfloras origin in the oldest deposits, it occurs frequently in brackish Permian 297±5Ma stratigraphic gap (SHRIMP age) and freshwater deposits (Duffin 1985, 2001; Cappetta 1987; lithofacies C Fischer 2008). There is the distinct possibility that many spe− (ca. 45 m) cies of Lissodus were either