Chemical Geology 342 (2013) 44–62

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Chemical Geology

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Oxygen and strontium isotopes from fossil shark teeth: Environmentaland ecological implications for Late Palaeozoic European basins

Jan Fischer a,⁎, Jörg W. Schneider a, Silke Voigt b, Michael M. Joachimski c, Marion Tichomirowa d,Thomas Tütken e, Jens Götze d, Ulrich Berner f

a TU Bergakademie Freiberg, Geologisches Institut, Bereich Paläontologie, Bernhard-von-Cotta Straße 2, 09599 Freiberg, Germanyb Goethe-Universität Frankfurt am Main, Institut für Geowissenschaften, Altenhöferallee 1, 60438 Frankfurt, Germanyc Geozentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg, Schlossgarten 5, 91054 Erlangen, Germanyd TU Bergakademie Freiberg, Institut für Mineralogie, Brennhausgasse 14, 09599 Freiberg, Germanye Universität Bonn, Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Poppelsdorfer Schloss, 53115 Bonn, Germanyf Bundesanstalt für Geowissenschaften und Rohstoffe, Geozentrum Hannover, Stilleweg 2, 30655 Hannover, Germany

⁎ Corresponding author. Tel.: +49 3731 393812; fax:E-mail address: j.fischer1@yahoo.de (J. Fischer).

0009-2541/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.chemgeo.2013.01.022

a b s t r a c t

a r t i c l e i n f o

Article history:Received 18 July 2012Received in revised form 23 January 2013Accepted 28 January 2013Available online 8 February 2013

Editor: U. Brand

Keywords:Oxygen isotopesStrontium isotopesBioapatiteFreshwater sharkCarboniferousPermian

Fossil shark remains occur in both marine and nonmarine Late Palaeozoic deposits, therefore their palaeo-ecology is controversial. The oxygen and strontium isotopic composition of biogenic fluorapatite in 179teeth, scales and spines predominantly of hybodontid (Lissodus) and xenacanthiform (Orthacanthus,Xenacanthus, Bohemiacanthus, Triodus) sharks from various Late Carboniferous (Moscovian) to Early Permian(Artinskian) basins of Europe are used as ecological tracers to decipher diadromous or obligate freshwaterlifestyle of the investigated taxa. The δ18OP values of the different shark teeth range from 11.7 to 20.2‰within the different basins with mean values of 16.9±0.5‰ for the Bohemian Massif, 16.2±0.8‰ for easternGermany, 18.2±1.0‰ for southwestern Germany, 18.5±0.7‰ for southern-central Spain, 17.6±0.4‰ forSardinia, and 16.6±0.5‰ VSMOW for the French Massif Central. The tooth δ18OP values from the basinsare mostly depleted by 1–5‰ relative to those of shark teeth from contemporaneous marine settings. Oxygenisotope signatures of co-occurring taxa do not show systematic differences excluding habitat effects fordifferent shark groups. However, distinctly higher δ18OP values from Puertollano and Saar–Nahe can be at-tributed to significant evaporative enrichment in 18O of the ambient water in the ancient lacustrine environ-ments due to a warm and dry climate and sufficient residence time in the basins. The strontium isotopiccomposition of the teeth varies between 0.70824 and 0.71216 with a mean value of 0.71031. These 87Sr/86Sr ratios are always more radiogenic in comparison to the 87Sr/86Sr record of seawater of their stratigraphicage. Overall, the investigated tooth samples yield low δ18OP and high 87Sr/86Sr values deviating frombioapatite values expected for contemporaneous marine vertebrates and typical for freshwater settings.This indicates a fully freshwater adapted lifestyle for a variety of fossil shark taxa in Late Palaeozoic Europeanbasins.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Fossil shark remains are abundant in Late Carboniferous and EarlyPermian deposits of continental basins of Europe being mostly repre-sented by isolated teeth (e.g., Schneider, 1985; Hampe, 1994;Soler-Gijón, 1997; Štamberg and Zajíc, 2008; Fischer et al., 2010).Analyses of the spatial taxa distribution revealed a highly diverse,widespread, and uniform shark-association within the European ba-sins during the latest Carboniferous (Gzhelian) (Schneider and Zajíc,1994; Schneider et al., 2000) that became increasing patchy duringthe Early Permian (Fischer et al., 2010; Fig. 1). According to thisobservation, nearly all Carboniferous basins were connected by a

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complex drainage system that gave aquatic vertebrates the possibilityfor exchange. However, the presence of shark remains in continentalbasins together with contradicting facies interpretations of sedimen-tary deposits led to different interpretations concerning a marineinfluence during the late Palaeozoic in Europe. Two contrary assump-tions exist about the palaeoecology of these ancient shark communi-ties. On one hand, they are considered to have been euryhaline fishesin marginal marine coastal, lagoonal to estuarine influenced environ-ments (Soler-Gijón, 1999; Schultze and Soler-Gijón, 2004; Schultze,2009; Carpenter et al., 2011). This view is based on the record of sev-eral members of specific fossil shark families frommarine strata, theirglobal occurrence, and the marine restriction of extant shark eggcapsules as well as analogies with modern diadromous sharks (seealso Soler-Gijón, 1993, 1997). The similarity of aquatic shark faunasin different European basins is explained by those authors assuming

Fig. 1. Palaeogeographic overview map of important Latest Carboniferous and Early Permian basins of Europe (modified from Roscher and Schneider, 2006) with the currentlyknown palaeobiogeography of xenacanthiformes, hybodontids, sphenacanthids (modified from Schneider and Zajíc, 1994; Fischer et al., 2010). Numbers in the circles refer tothe localities in Figs. 2, 4, 5, and Tables 1–3. Shark taxa: B — Bohemiacanthus, L — Lissodus, O — Orthacanthus, P — Plicatodus, S — Sphenacanthus, T — Triodus, and X — Xenacanthus;below the horizontal line — occurrences during Stephanian C (late Gzhelian–early Asselian), and above the horizontal line — occurrences during Rotliegend (middle Asselian–earlyArtinskian). Basins: AU — Autun basin, BLG — Blanice Graben, BCG — Boskovice Graben, BU — Bourbon l'Archambault basin, CA — Carpathian basin, DB — Donetsk basin, DÖ —

Döhlen basin, EB — Erzgebirge basin, FL — Flechting Block, FR — Franconian basin, GP — Guardia Pisano basin, IF — Ilfeld basin, KP — Krkonoše Piedmont basin, LC — Lu Caparonibasin, LO — Lodève basin, MO — Montceau les Mines basin, NGVC — North German Volcanite Complex, NS — North Sudetic basin, PD — Perdasdefogu basin, PU — Puertollanobasin, RÜ — Rügen, SB — Saale basin, SH — Sprendlinger Horst, SNB — Saar–Nahe basin, ST — St. Etienne basin, SV — Salvan-Dorénaz basin, TF — Thuringian Forest basin, WCB —

Western and Central Bohemian basins, WE — Weissig basin, and ZÖ — Zöbingen.

45J. Fischer et al. / Chemical Geology 342 (2013) 44–62

marine conditions prevailing throughout these basins allowingmigration along marine seaways. In contrast, the second hypothesisnegates any marine influence, and assumes the full adaption ofthese sharks to an obligate freshwater lifestyle (Schneider and Zajíc,1994; Schneider et al., 2000) based on sedimentological criteria aswell as palaeogeographical and ecological arguments (see alsoSchneider and Reichel, 1989; Schneider, 1996; Boy and Schindler,2000; Fischer et al., 2010). Accordingly, faunal exchange betweenbasins is assumed to have occurred mainly within drainage systems,albeit faunal exchange between river mouths via coastal waters isnot completely excluded (Schindler and Hampe, 1996; Schneideret al., 2000).

Analyses of the phosphate oxygen (δ18OP) and strontium (87Sr/86Sr)isotope compositions of shark teeth are a worthwhile geochemical ap-proach to address this controversy, and test the two different modelsfor the shark palaeoecology and hence basin hydrography. Biogenicfluorapatite of fossil shark tooth enameloid is considered a valuablepalaeoecological and palaeoenvironmental archive (e.g., Kolodny andRaab, 1988; Kolodny and Luz, 1991; Koch et al., 1992; Vennemannand Hegner, 1998; Kohn and Cerling, 2002; Lécuyer et al., 2003;Kocsis et al., 2007, 2009; Zacke et al., 2009; Tütken et al., 2011) due tothe preservation of the aqueous conditions (i.e. isotope composition ofthe ambient water) at the time of tooth formation (Longinelli andNuti, 1973; Kolodny et al., 1983; Schmitz et al., 1991; Vennemannet al., 2001). Contrary to other vertebrate bioapatites, shark teethpossess several advantages as palaeoenvironmental archives: (1) theyare the most common phosphatic vertebrate remains in aquaticsediments with a wide spatial and stratigraphical distribution sincethe Devonian (Ginter et al., 2010), (2) the body temperature is relatedto the ambient water temperature because of shark ectothermy(Speers-Roesch and Treberg, 2010), (3) the body fluid of aquaticanimals is in isotopic equilibrium with the ambient water contrary to

semi-aquatic and terrestrial vertebrates, whose body waters areenriched in 18O by up to 2‰ (Amiot et al., 2007; Bernard et al., 2010),(4) the δ18OP of the tooth enameloid seems to be independent frommetabolic fractionation effects (the so-called vital effects) (Kolodnyet al., 1983), (5) no taxon-specific fractionation for sharks is reported(Vennemann et al., 2001), and (6) shark enameloid consists mainly ofstable fluorapatite (Ca5(PO4)F) with inferior amounts of hydroxyl-and carbonate apatite (Vennemann et al., 2001; Enax et al., 2012) com-pared to themetastable carbonate containing hydroxylapatite of bones.In addition, the fluorapatite of shark teeth has been considered to bemore robust against diagenetic alteration than either dentine or bonebecause of its high degree of mineralisation, large apatite crystal size,the low content of organic compounds, and the strong chemical bondbetween phosphor and oxygen (Kohn et al., 1999; Sharp et al., 2000;Kohn and Cerling, 2002; Enax et al., 2012). Hence original δ18OP valuesare likely preserved in fossil shark teeth. The rapid, lifelong toothreplacement in sharks takes place within days to weeks (Berkovitz,2000; Botella et al., 2009b). This makes their teeth short-term recordersof the isotope composition and temperature of the ambient water, inwhich the teeth were mineralised. Thus, tooth apatite of shark teethformed in thermally and geochemically different water masses vary inδ18OP and 87Sr/86Sr between marine and freshwater environments(Schmitz et al., 1991; Kohn et al., 1999; Koch, 2007), which enablesthe tracking of euryhaline or obligate habitat preferences in fossil spe-cies (Kocsis et al., 2007; Klug et al., 2010; Fischer et al., 2011, 2012).

Besides teeth, chondrichthyan scales as well as spines providefurther material for study since they are also covered by a hyper-crystalline cap on their exposed parts (Reif, 1978; Cappetta, 1987).In particular, spines (fin spines in hybodontids, head/dorsal spinesin xenacanthiformes) as livelong growing, nonreplaced hard tissuescomprise an as yet unexplored isotopic time series of a shark's entirelife, in addition to the short-term ‘geochemical snapshots’ from teeth

46 J. Fischer et al. / Chemical Geology 342 (2013) 44–62

and/or scales. During growth new dentine was mainly added proxi-mally of the spine with the inner distal part (apex) being the oldestpart of the spine (Maisey, 1978; Soler-Gijón, 1999). Resultingincremental growth layers of spines provide an opportunity to tracevariations in its δ18OP during the life time of the shark.

Hitherto, the record of δ18OP and 87Sr/86Sr from Late Palaeozoicshark remains is sparse, mostly unsystematic, and from outside ofEurope (Kolodny and Luz, 1991; Schmitz et al., 1991; Calder, 1998;Falcon-Lang, 2005; Carpenter et al., 2011). Here, the first comprehen-sive δ18OP and 87Sr/86Sr dataset is presented from teeth, scales andspines of fossil sharks from several continental basins of western,southern, and central Europe as well as from marine shark teethfrom the European part of Russia (Fig. 1). The investigated samplescover a stratigraphic range from the late Early Carboniferous(Serpukhovian) to the late Early Permian (Artinskian) (Fig. 2).Cathodoluminescence microscopy and spectroscopy were made inorder to test the preservational state of the analysed bioapatite. Theisotope compositions of well-preserved specimens are interpretedto infer their lifetime habitats and possible mobility patterns of theinvestigated shark taxa evaluating the aforementioned two palaeo-ecological and environment models.

2. Geological setting

The analysed shark material derives from 21 localities of 13Central and East European basins and regions (Fig. 1) covering atime span of about 40 Ma from the Late Mississippian (Serpukhovian)to the Early Permian (Artinskian; Fig. 2).

Fig. 2. The stratigraphic position of the localities yielding the shark teeth and spine samples ainterglacial periods while white areas represent glacial periods, according to Roscher and S

2.1. Puertollano basin (1)

The Puertollano basin in the Central Iberian Zone of southernSpain exposes conglomerates, sandstones, mudstones, siderite car-bonates, pyroclastics, coal seams and black shales of Stephanian C(Gzhelian/Asselian) age (Schneider et al., 2000; Colmenero et al.,2002). Although, the coal seams are generally considered to haveformed under lacustrine endorheic conditions (Wagner, 1989;Borrego et al., 1996; Jiménez et al., 1999; Colmenero et al., 2002),the occurrence of shark remains in black shales together with sedi-mentological and geochemical data have been repeatedly interpretedas paralic indicators (Soler-Gijón, 1993, 1997; Alastuey et al., 2001;Soler-Gijón and Moratalla, 2001).

2.2. Bourbon l'Archambault basin (2)

The former open-cast coal mine of Buxières-les-Mines is situatedat the southern border of the Bourbon l'Archambault basin in thenorthern part of the French Massif Central. The basin fill consists ofconglomerates, alluvial arkoses, palustrine deposits with coal seams,followed by bituminous black shales and fluvial sandstones; interca-lated are thin horizons of intermediary pyroclastics (Roscher andSchneider, 2006). The shark teeth and spines derive from black shalesof the Buxières Formation, which have been biostratigraphically andisotopically dated as Sakmarian in age (Roscher and Schneider,2005; Schneider and Werneburg, 2006). While, generally the Bour-bon l'Archambault deposits are interpreted to have formed underfreshwater conditions (Steyer et al., 2000; Roscher and Schneider,

nalysed in this study. Numbers refer to basin numbers in Fig. 1. Grey shaded areas markchneider (2006) and Roscher (2009).

47J. Fischer et al. / Chemical Geology 342 (2013) 44–62

2006), a marine influence has been supposed based on comparisonsof aquatic faunas (Schultze and Soler-Gijón, 2004; Schultze, 2009).

2.3. Guardia Pisano basin (3)

Erosional remnants of this basin are located in southwesternSardinia, Italy. The basin fill consist of about 70 m of sandstones,grey to black pelites, and shark-remain yielding limestones withintercalated volcaniclastic deposits unconformably overlain by redcoarse clastics (Barca and Costamagna, 2006; Ronchi et al., 2008).The pyroclastics have been radiometrically U–Pb dated usingSHRIMP as 297±5 Ma in age, which supports a Gzhelian to Asselianage (Pittau et al., 2002; Fischer et al., 2010).

2.4. Perdasdefogu basin (4)

This half-graben basin is situated in southeastern Sardinia, Italy.The 120 m thick fining-upward sequence of the Rio su Luda Forma-tion starts with basal conglomerates on Variscan basement followedby an alternation of sandstones, siltstones and black shales with inter-calated pyroclastics, and bituminous black limestones and cherts ontop (Ronchi et al., 1998, 2008). Limestones with isolated fish remainsare exposed at the locality Ortu Mannu. Based on the occurrence ofbranchiosaurid amphibians the formation is dated to be late Asselian(Werneburg et al., 2007).

2.5. Saar–Nahe basin (5)

This largest Late Palaeozoic basin in Europe is situated at the south-eastern margin of the Rhenish Slate Mountains in western Germany.The basin fill comprises about 4500 m Late Carboniferous and about3000 m Permian (Rotliegend) sediments and volcaniclastics. The sed-iments of the Rotliegend are subdivided into the older Glan Subgroup(Gzhelian–Sakmarian) comprising lacustrine, deltaic to floodplaindeposits mainly in grey facies, and the younger Nahe Subgroup(Sakmarian–Wordian) consisting of volcaniclastics and reddish alluvi-al fan to playa deposits (Schindler, 2007; Boy et al., 2011; Schäfer,2011). For the Glan Subgroup the Altenkirchen locality exposes theFriedelhausen lake horizon of the early Asselian Remigiusberg Forma-tion (Boy and Schindler, 2000; Schneider and Werneburg, 2006). Forthe Glan Subgroup in the Lauterecken Formation the Blochersberglocality exposes the Odenbach lake horizon, while in the youngerMeisenheim Formation the Unkenbach and Alsenz localities exposethe Breitenheim and Raumbach lake horizons, respectively (Boyet al., 2011). The Sobernheim lake horizon is situated in the red bedsof the Wadern Formation of the Nahe Subgroup; for which a middleArtinskian age is assumed (Schneider and Werneburg, 2006, 2012).

2.6. Sprendlinger Horst swell (6)

Red alluvial fan to playa sediments with intercalated volcani-clastics as lateral equivalents of the basal Nahe Subgroup were deposit-ed on this swell (Marell, 1989; Kowalczyk et al., 1999). At theGötzenhain locality a 0.5 m thick horizon of oolitic to stromatoliticwell-bedded limestones (“Plattenkalk”) yields fish remains (Schindler,2010), and is dated as Sakmarian based on amphibians (Werneburg,2008).

2.7. Thuringian Forest basin (7)

Situated on the Mid-German Crystalline Zone the basin is filledwith up to 6000 m thick siliciclastics and volcaniclastics of latestCarboniferous (Gzhelian) to Late Permian (Wuchapingian) age(Lützner et al., 2007). The Moosbach and Silbergrund localities ofthe Möhrenbach Formation expose red and grey arkosic conglomer-ates and sandstones followed by aquatic-vertebrate-bearing black

shales, thin limestone beds, and minor coal seams. A late StephanianC (transitional Gzhelian/Asselian) age is based on amphibians(Werneburg and Schneider, 2006). The Sperbersbach locality exposesone of the black shale horizons in the Lower Rotliegend GoldlauterFormation, dated as middle Asselian by insects (Schneider andWerneburg, 2006, 2012).

2.8. Saale basin (8)

It represents a peri-montaneous basin on theMid-German Crystal-line Zone in the northeastern extension of the Thuringian Forest basin.Interrupted by several hiatuses, the basin fill consist of 2200 m thicksiliciclastics and volcaniclastics of Late Carboniferous (Stephanian)and Permian age deposited on older Early and Late Carboniferous sed-iments, which are part of the paralic influenced Variscan foreland(Schneider and Romer, 2010). Isolated fish remains were recoveredfrom a limestone, Stephanian C (transitional Gzhelian/Asselian) inage (Schneider and Werneburg, 2006; Werneburg and Schneider,2006; Schneider and Werneburg, 2012), at the Dobis locality, whichexposes mainly red beds as well as grey palustrine coal seams andblack shales of the Siebigerode Formation.

2.9. Central and Western Bohemian basins (9)

Situated on top of the Bohemian Massif, Czech Republic, theBohemian basins are filled with about 1500 m of grey and red alluvialto palustrine sediments with coal, black shales and horizons ofpyroclastics of Moscovian to Gzhelian (Westphalian C to StephanianC) age (Opluštil and Pešek, 1998; Pešek, 2004). The Nýřany localityexposes late Moscovian (Westphalian D) coal seams and vertebrate-rich sapropelites of the Kladno Formation. The Kounov localityexposes coal seams and vertebrate bearing sapropelites of the earlyGzhelian (Stephanian B) Slaný Formation (Schneider and Werneburg,2006; Štamberg and Zajíc, 2008; Schneider and Werneburg, 2012).

2.10. Krkonoše Piedmont basin (10)

This basin is one of the Sudetic basins that are east of the Centraland Western Bohemian basins. Late Moscovian (Westphalian D) toearly Gzhelian (Stephanian B) sediments of around 650 m thicknessare developed in alluvial grey and red bed facies similar to theBohemian basins. The Permian basin fill of mainly alluvial red bedsof about 2000 m yields several large hiatuses (Opluštil and Pešek,1998; Pešek, 2004). The Krsmol locality exposes the red pelitic,partially tuffitic, Plouznice horizon of the Gzhelian (Stephanian B/C)Semily Formation (Štamberg, 2001; Schneider and Werneburg,2006, 2012).

2.11. Donetsk basin (11)

This basin is located in the central part of the northwest–southeasttrending Dnieper–Donets rift basin of the Eastern European Craton,which is linked via the Uralian seaway to the Tethys. It is filled withDevonian to Early Permian fluvio-deltaic and nearshore marinemixed siliciclastic–calcareous sediments of 20 km thickness. Sharkteeth occur in brackish, marine, and lacustrine limestones of differentage, whereby marine limestone and coal beds serve as marker hori-zons (Eros et al., 2012). The age of individual beds is determined bybiostratigraphy and calibrated with radiometric methods. According-ly, the Kalinovo locality exposes limestones M7 and M8 (middleMoscovian [Westphalian C]), and limestone P1 (early Gzhelian[Stephanian B]), and Luganskoje locality exposes limestone P6(Gzhelian [Stephanian B/C]) (Schneider and Werneburg, 2006;Davydov et al., 2010).

48 J. Fischer et al. / Chemical Geology 342 (2013) 44–62

2.12. Moscow Syneclise (12) and the South Urals (13)

These two regions represent unequivocal marine facies from theMississippian–Pennsylvanian transition (Namurian A–B) in the ma-rine realm of the East European Platform. In the Moscow Syneclise

Fig. 3. Cathodoluminescence microphotographs of polished thin sections showing the enameFischer et al., 2010 (A) and Triodus kraetschmeri Hampe, 1989 (B). The enameloid shows thpears brown to orange. The CL spectra of enameloid (A1) and dentine (A2) show a broad banbetween 480 and 890 nm that are distinct smaller for enameloid than for dentine (the grey lof the outer layer and dentine in Triodus (B1–2) demonstrate comparable robustness of the

at the Kalinovskie Vyselki locality shark teeth and conodonts derivefrom marine siltstones of early Serpukhovian age (Ivanov andGinter, 1996; Duffin and Ivanov, 2008). The Sholak-Say locality atthe eastern side of the South Urals exposes deep-water limestonesof Bashkirian age (Ivanov, 1996).

loid/outer hypermineralised cap and dentine of tooth specimens of Lissodus sardiniensise dark violet luminescence of intrinsic apatite whereas the CL colour of the dentine ap-d emission centred at ca. 585 nm due to Mn2+ and characteristic REE3+ emission peaksow spectra-line in A2 represents the scaled intensity counts of A1). The same CL spectrahypermineralised cap to classical shark enameloid.

Table 1Mean δ18OP values (in VSMOW) and 87Sr/86Sr ratios of shark tooth apatite from the dif-ferent localities. CZE, Czech Republic; ESP, Spain; GER, Germany; FRA, France; ITA, Italy;RUS, Russia; and UKR, Ukraine. Locality numbers refer to basin numbers in Fig. 1.Palaeotemperature estimates TW are based on the equations of Pucéat et al. (2010).

Locality Meanδ18OP

Std.(1σ)

n Mean87Sr/86Sr

n TW(°C)

Kalinovskie Vyselki, 12, RUS 19.6 0.6 8 0.70818 5 32.2Sholak-Say, 13, RUS 21.6 – 1 – – 19.5Nýřany, 9, CZE 16.9 0.4 5 0.71045 3 43.5Kounov, 9, CZE 16.8 0.5 16 0.71029 5 44.0Krsmol, 10, CZE 17.6 0.2 3 0.70998 1 40.6Kalinovo, 11, UKR 15.0 0.8 11 0.70881 7 47.4Luganskoje, 11, UKR 14.8 0.3 2 0.70974 2 52.4Puertollano, 1, ESP 18.5 0.7 7 0.71190 3 32.6Guardia Pisano, 3, ITA 17.6 0.4 23 0.71032 4 36.4Ortu Mannu, 4, ITA 12.4 0.3 4 – – 58.4Moosbach.,7, GER 15.7 0.7 7 0.70973 2 44.4Silbergrund, 7, GER 12.8 0.7 17 0.70963 1 56.7Sperbersbach, 7, GER 13.0 1 3 0.71784 2 60.0Dobis, 8, GER 15.3 0.7 4 0.71028 1 46.1Altenkirchen, 5, GER 18.6 0.5 15 0.71112 5 32.2Blochersberg, 5, GER 16.3 1 8 0.71077 4 46.1Unkenbach, 5, GER 18.4 0.6 10 0.71030 3 37.3Alsenz, 5, GER 18.2 0.3 3 0.71046 3 38.1Götzenhain, 6, GER 14.2 1 4 0.70830 4 55.0Sobernheim, 5, GER 16.1 – 1 0.70995 1 42.7Buxiéres, 2, FRA 16.6 0.5 17 0.71065 4 40.6

49J. Fischer et al. / Chemical Geology 342 (2013) 44–62

3. Material and analytic methods

Altogether, 179 tooth, scale and spine samples of different Late Car-boniferous and Early Permian shark taxawere analysed. Themajority ofthe fossil material derives from the hybodontid Lissodus Brough, 1935and the diplodoselachid Orthacanthus Agassiz, 1843, some specimensbelong to xenacanthids (Xenacanthus Beyrich, 1848, Triodus Jordan,1849 [sensu stricto — see Schneider, 1996], Bohemiacanthus Schneiderand Zajíc, 1994), sphenacanthids (Sphenacanthus Agassiz, 1843,Turnovichthys Štamberg, 2001), symmoriids (Stethacanthus Newberry,1889), falcatids (Stethacanthulus Zangerl, 1990), and ctenacanthids(GlikmaniusGinter et al., 2005). In addition, one samplewith conodontscomes from Kalinovskie Vyselki. The material was either obtainedfrom collected and handpicked screen washed residues (processingwith 10% formic acid) or was taken from collections of the followingfacilities: TU Bergakademie Freiberg, Naturhistorisches MuseumSchloss Bertholdsburg Schleusingen,Museum für Naturkunde Berlin,Generaldirektion Kulturelles Erbe Mainz/Landessammlung fürNaturkunde Mainz, Museum of Eastern Bohemia, National MuseumPrague, St. Petersburg University, and Lugansk National University“Taras Shevchenko”, as well as from private collections of T. Schindler(Spabrücken), and K. Krätschmer (Odernheim).

The greatest possible number of oxygen isotope analyses wasperformed on single teeth. In order to obtain sufficient enameloid orenameloid-rich material (0.5–1.2 mg) of the small-sized PalaeozoicLissodus teeth (≤1 mm mesiodistal), oxygen isotope analyses wereperformed on samples comprising several individual crown frag-ments (Supplement). Material from spine growth layers was ob-tained as powder using a micro drill. Fluorapatite was dissolved innitric acid and the phosphate group precipitated as trisilverphosphate(Ag3PO4) (Joachimski et al., 2006, 2009). Isotope analyses wereperformed in triplicate using a high-temperature conversion-elemental analyser (TC-EA) coupled online to a ThermoFinniganDelta Plus mass spectrometer in Erlangen, Germany. All values arereported in ‰ relative to VSMOW (Vienna Standard Mean OceanWater) with reproducibility better than ±0.2‰ (1σ). The value ofthe internationally used standard NBS 120c is still debated withreported values around 21.7‰ VSMOW (21.5±0.5‰ VSMOW,Chenery et al., 2010, 21.7±0.2‰ VSMOW, Lécuyer et al., 1993,1996, 21.8±0.2‰ VSMOW, O'Neil et al., 1994; Fricke et al., 1998;Halas et al., 2011, and 22.6±0.1‰ VSMOW, Vennemann et al.,2002). In this study, NBS 120c was measured as 22.4±0.2‰VSMOW (n=64). All measured δ18OP values were normalised tothe accepted value of NBS 120c of 21.7‰ by deducting 0.7‰.

Strontium isotope analyses were performed on a selection of toothsamples used for oxygen isotope analyses (n=62) (Supplement).About 0.5–8.0 mg of tooth material was decomposed in 2.5 Nhydrochloric acid, passed through Sr-Spec preconditioned cation-exchange micro columns (Pin and Bassin, 1992), and loaded with atantalum activator onto pre-degassed tungsten filaments. The 87Sr/86Sr ratios were determined on a Finnigan MAT 262 mass spectrome-ter at the TU Freiberg, Germany. Samples were measured in 20 blockswith mean analytical uncertainty (1σ) for the measured 87Sr/86Sr ra-tios b0.00002 (n=56). All samples were normalised to 86Sr/88Sr=0.1194. Repeated analyses of the NBS 987 standard gave a value of0.71020±0.00003 (n=19). All measured 87Sr/86Sr of the sampleswere normalised to the accepted value for NBS 987 of 0.71025(Faure and Mensing, 2004) by adding +0.00005.

Cathodoluminescence (CL)microscopy and spectroscopy of selectedtooth samples from most localities were performed on carbon-coatedpolished thin sections using a ‘hot cathode’ CL microscope at 14 kV ac-celerating voltage with a current density of about 10 μA/mm2 (Neuseret al., 1995; Kempe and Götze, 2002). CL images were captured onlineby a KAPPA 961-1138 CF 20 DXC digital video camera with coolingstage. An Acton Research SP-2356 digital triple-grating spectrographwith a Princeton Spec-10 CCD detector attached to the CL microscope

recorded the CL spectra in the wavelength range 380–1000 nm. Allmeasurements were made under standardised conditions (wavelengthcalibration by anHg lamp, spotwidth 30 μm,measuring time 2 s) at theTU Freiberg, Germany.

4. Results

4.1. Cathodoluminescence

The inner dentine core of the teeth differs in its yellow orange tobrown luminescence from the intrinsic blue hypermineralised outerenameloid layer (Fig. 3A). The CL spectra show a broad emissionband of Mn2+ (585 nm) and characteristic REE emission peaks be-tween 480 and 890 nm (Fig. 3A) resting on the Mn2+ band, wherebythe REE emission intensity of the enameloid layer (Fig. 3A1) is dis-tinctly lower than that for dentine (Fig. 3A2). Differences in intensitygenerally change from one locality to another.

Most Palaeozoic shark teeth possess a hypermineralised layer ofsingle crystallite enameloid (SCE) (Reif, 1973; Gillis and Donoghue,2007; Botella et al., 2009a). Xenacanthiform sharks (diplodoselachids,xenacanthids), instead, lack such an enameloid cap (Hampe, 1991;Hampe and Long, 1999; Hampe, 2003; Stiernagle and Johnson,2004; Ginter et al., 2010) but have a hypermineralised outer layer oforthodentine resembling SCE (Schneider, 1996; Johnson, 2003; Gillisand Donoghue, 2007; Turner and Burrow, 2011). In this study, mea-sured CL spectra of the outer layer and dentine in xenacanthiformteeth show the same pattern of REE enrichment as between SCE anddentine in hybodontid sharks (Fig. 3B). This indicates comparable highcompactness, low organic carbon content, and large crystallites of theouter hypermineralised layer. The preservational state of the outerorthodentine layer in xenacanthiform teeth, thus, appears to be compa-rable to the robust SCE, and has the high potential to preserve the prima-ry oxygen isotope composition in Palaeozoic bioapatite. Therefore, it wasused for isotope analyses just as ‘ordinary’ shark tooth enameloid.

4.2. Oxygen isotope composition

The shark teeth δ18OP values show a large variability in the differ-ent European Palaeozoic basins ranging from 11.7 to 20.2‰ with

50 J. Fischer et al. / Chemical Geology 342 (2013) 44–62

different mean δ18OP values for each basin (Table 1, Fig. 4). Further-more, variability in δ18OP is also observed between different strati-graphic levels within the same basin (Table 1), especially amonglocalities of the Saar–Nahe basin, and between shark taxa of one local-ity (Table 2). The highest δ18OP values measured in this study arefrom Puertollano, Altenkirchen and Unkenbach with an overallmean δ18OP value of 18.6±0.6‰ VSMOW (Table 1), whereas the low-est values occur in specimens from Ortu Mannu, Silbergrund andSperbersbach with a mean δ18OP value of 12.8±0.7‰ VSMOW(Table 1). Samples from all other localities have intermediate meanvalues (16.7±1.3‰ VSMOW). Additionally, the marine samplesfrom the East European Platform provide high mean δ18OP values of19.6±0.6‰ VSMOW (n=8) for shark teeth and 21.2‰ VSMOW forconodont bulk material from the Kalinovskie Vyselki quarry of theMoscow region as well as 21.6‰ VSMOW for shark material from

Fig. 4. Box and Whisker plot of tooth δ18OP for the different localities (A) and the differentgrey shaded area while the lower limit of the grey field marks the lowest marine values knowand sharks from the East European Platform are shown for comparison. Data sets regardedorder with oldest left; bottom numbers refer to basin numbers in Fig. 1.

Sholak-Say of the South Urals. These δ18OP values are higher thanthose of shark teeth from all other continental basins except for a sin-gle value (20.2‰) from Puertollano (Fig. 4).

4.3. Strontium isotope composition

The 87Sr/86Sr ratios from all basins vary between 0.70824 and0.71216 (Fig. 5, Table 1). However, most of the values are clearlywithin a more narrow range of 0.70951 and 0.71119 with a meanvalue of 87Sr/86Sr=0.71036 (n=43). The most radiogenic valuesare recorded from Puertollano (mean 87Sr/86Sr=0.71190, n=3)(Fig. 5), and Sperbersbach (0.72522; not shown in Fig. 5). More-over, two different groups of 87Sr/86Sr, Kalinovo (mean 87Sr/86Sr=0.70881, n=7) and Götzenhain (mean 87Sr/86Sr=0.70830, n=4),have values lower than the mean range but are still more radiogenic

shark genera from the basins (B). The range of full marine conditions is marked by then from the late Carboniferous (Joachimski et al., 2006). Marine δ18OP data of conodontsas diagenetic altered are encircled by a dashed line. Data are arranged in stratigraphic

Table 2Mean δ18OP values (in VSMOW) and 87Sr/86Sr ratios of tooth apatite from specific shark taxa. CZE, Czech Republic; ESP, Spain; GER, Germany; FRA, France; ITA, Italy; RUS, Russia;and UKR, Ukraine. Locality numbers refer to basin numbers in Fig. 1.Palaeotemperature estimates TW are based on the equations of Pucéat et al. (2010).

Species Locality Meanδ18OP

Std.(1σ)

n Mean87Sr/86Sr

n TW (°C)

Stethacanthus Kalinovskie Vyselki, 12, RUS 19.4 0.3 2 0.70810 2 33.0Glikmanius Kalinovskie Vyselki, 12, RUS 19.8 0.6 6 0.70818 3 31.3Stethacanthulus Sholak-Say, 13, RUS 21.6 – 1 – – 19.5Orthacanthus Nýřany, 9, CZE 16.9 0.4 5 0.71045 3 43.6Orthacanthus Kounov, 9, CZE 16.8 0.5 16 0.71029 5 44.0Turnovichthys Krsmol, 10, CZE 17.6 0.2 3 0.70998 1 40.6hybodont indet Kalinovo, 11, UKR 15.5 0.3 5 0.70881 3 45.3cladodont indet Kalinovo, 11, UKR 14.3 0.3 5 0.70880 3 50.3cladodont indet Kalinovo (P1), 11, UKR 16.3 – 1 0.70896 1 46.1Orthacanthus Luganskoje, 11, UKR 14.8 0.3 2 0.70974 2 52.4Lissodus Puertollano, 1, ESP 18.0 – 1 – – 34.7Triodus Puertollano, 1, ESP 18.3 – 1 – – 33.5Orthacanthus Puertollano, 1, ESP 18.6 0.8 5 0.71190 3 32.2Lissodus Guardia Pisano, 3, ITA 17.6 0.4 23 0.71032 4 36.4Bohemiacanthus Ortu Mannu, 4, ITA 12.4 0.3 4 – – 58.4Lissodus Moosbach, 7, GER 15.7 0.7 7 0.70973 2 44.4Orthacanthus Silbergrund, 7, GER 12.8 0.7 17 0.70963 1 56.7Lissodus Dobis, 8, GER 16.6 – 1 – – 40.6Xenacanthus Dobis, 8, GER 15.2 0.1 3 0.71028 1 46.5Bohemiacanthus Sperbersbach, 7, GER 13.0 1 3 0.71784 2 60.0Lissodus Altenkirchen, 5, GER 18.6 0.6 9 – – 32.2Xenacanthus Altenkirchen, 5, GER 18.3 – 1 – – 33.5Sphenacanthus Altenkirchen, 5, GER 18.6 0.3 5 0.71112 5 32.2Xenacanthus Blochersberg, 5, GER 16.4 0.1 3 0.71071 2 45.7Triodus Blochersberg, 5, GER 16.2 1.1 4 0.71083 2 46.5xenacanthid indet. Blochersberg, 5, GER 18.5 – 1 – – 36.8Orthacanthus Unkenbach, 5, GER 18.4 0.6 10 0.71030 3 37.3Orthacanthus Alsenz, 5, GER 18.2 0.3 3 0.71046 3 38.1Bohemiacanthus Götzenhain, 6, GER 14.2 1 4 0.70830 4 55.0Triodus Sobernheim, 5, GER 16.1 – 1 0.70995 1 42.7Lissodus Buxiéres, 2, FRA 16.6 0.5 9 0.71070 3 40.6Orthacanthus Buxiéres, 2, FRA 16.6 0.5 8 0.71061 1 40.6

51J. Fischer et al. / Chemical Geology 342 (2013) 44–62

than the expected strontium isotope composition of contemporane-ous seawater (Fig. 5). The 87Sr/86Sr ratios, measured on samplesfrom Kalinovskie Vyselki (mean 87Sr/86Sr=0.70818, n=5), are theonly values that match the seawater strontium isotope compositionof their stratigraphic age (0.70812; Denison et al., 1994) (Fig. 5).There is no trend in the distribution of the 87Sr/86Sr ratios withinor between the different basins, neither spatial nor temporal.

Fig. 5. 87Sr/86Sr ratios of teeth and spines from the different localities in comparison to the colevel (grey bars after data from Denison et al., 1994; Veizer et al., 1999; Korte et al., 2006).diagram. The analytical error is smaller than the symbol size. EEP, East European Platform. Dabers in Fig. 1.

5. Discussion

5.1. Preservational status of the bioapatite isotope composition

For palaeoclimatological or palaeoecological interpretations thepreservation of the primary isotope ratios has to be ascertained.Shark tooth enameloid is usually considered to be most resistant

ntemporaneous seawater strontium isotopic composition of the according stratigraphicThe highest measured value from Sperbersbach (0.72522) is outside the scope of thista arranged in stratigraphic order with oldest left; bottom numbers refer to basin num-

Fig. 6. δ18OP values of outer hypermineralised layer (equals ‘normal’ shark enameloid)and dentine from four teeth of Orthacanthus (Lebachacanthus) senckenbergianusFritsch, 1889 (LE UNK 1–2, 5284, 5286) from Unkenbach, and one tooth of axenacanthid indet. (XE OD 1) from Blochersberg, both Saar–Nahe basin. δ18OP valuesof outer hypermineralised layer are only 0.05 to 0.8‰ higher than the respective den-tine values from the same teeth.

52 J. Fischer et al. / Chemical Geology 342 (2013) 44–62

against diagenetic alteration compared to bone or dentine due to itshigh crystallinity of the bioapatite, and low organic content(Kolodny and Raab, 1988; Sharp et al., 2000; Koch, 2007; Kohnand Dettman, 2007; Enax et al., 2012). However, the stability ofenameloid has been repeatedly questioned (e.g., Kohn et al., 1999;Zazzo et al., 2004; Kocsis et al., 2009). Moreover, isotopic exchangewith pore waters during diagenesis may affect poorly ordered phasesof apatite and change primary 87Sr/86Sr values (Hoppe et al., 2003;Martin and Scher, 2004). Various approaches and indicators havebeen proposed to evaluate the preservational state of bioapatite(e.g., Shemesh, 1990; Habermann et al., 2000; Lécuyer et al., 2003;Eagle et al., 2011; Gehler et al., 2011; Thomas et al., 2011; Tütken,2011; Tütken and Vennemann, 2011) but to date there is no unequiv-ocal method to ensure pristine preservation (Pucéat et al., 2004;Tütken et al., 2008; Joachimski et al., 2009; Herwartz et al., 2011).

Two different points argue for a preservation of the originalisotope composition in the bioapatite from most localities. A distinctdiagenetic overprint should normally result in a homogenisation ofthe isotope signatures. The observed intra-site variability, however,shows heterogeneity in the δ18OP (up to 2‰; Fig. 4) and 87Sr/86Sr(Fig. 5) values that appear comparable to biological variationsmeasured in recent shark teeth (Vennemann et al., 2001; Kocsiset al., 2009), and to data measured from other fossil localities(Vennemann and Hegner, 1998; Fischer et al., 2012). The observedrange in δ18OP and 87Sr/86Sr argues for biological, ecological andsource effects being responsible for this variability rather than diage-netic alteration.

In addition, CL microscopy and spectroscopy were applied toevaluate possible diagenetic processes due to the spatially-resolveddetection of traces of rare earth elements (REE) in apatite(Habermann et al., 2000; Ségalen et al., 2008). In-vivo REE concentra-tions in shark tooth apatite are usually very low, while a strongincorporation in the apatite lattice may hint at early diagenetic ex-change with ambient fluids post mortem (Staudigel et al., 1985;Vennemann et al., 2001; Kocsis et al., 2009; Zacke et al., 2009). LowREE concentrations in apatite are characterised by an intrinsic blue lu-minescence colour (Habermann et al., 1999), whereas the substitu-tion of REE3+ (Dy, Ho, Sm, Eu, Tm, Nd) and/or Mn2+ for Ca2+

results in orange to brown luminescence colours (Gaft et al., 1996;Habermann et al., 1999; Ségalen et al., 2008). However, in any caseit has to be considered that oxygen, strontium, and REE are incorpo-rated into biogenic apatite through different pathways, and are likelyto behave differently during burial and diagenesis. While oxygen andstrontium isotope composition are acquired during sharks life, REEare indeed mainly incorporated into bioapatite during diagenetic pro-cesses, but through pathways that are most probably different thanthe processes that can induce a modification of the original oxygenand strontium isotopic composition (Martin and Scher, 2004). There-fore, CL provides only an empirical indication and no final evidencefor occurrence or absence of diagenetic alteration. The enameloid/outer layer of hybodont and xenacanthiform teeth (Fig. 3A, B) showa blue to dark violet luminescence, characteristic for a low degree ofREE uptake. Thus, the preservation of original isotope compositionsin these specimens is likely. In contrast, the dentine of the sametooth is characterised by an orange to brown luminescence(Fig. 3B). Related REE3+-peaks between 400 and 900 nm rest on adistinct Mn2+-band (Fig. 3A1–2, B1–2). Intensity counts of the CLspectra always show an enrichment of up to an order of a magnitudein REEs for the dentine compared to the more compact enameloid/outer layer (Fig. 3A2, B2).

To determine if enameloid and dentine yield significantly differentδ18OP values due to their different resistance against diagenetic alter-ation both dental tissues have been sampled and analysed separatelyfor several larger Orthacanthus (Lebachacanthus) teeth (LE UNK 1–2,5284, 5286) and one xenacanthid tooth (XE OD 1) from the Saar–Nahebasin. Accordingly, the δ18OP values of outer hypermineralised layer are

only slightly higher (b0.8‰) than those of respective dentine from thesame teeth (Fig. 6). Offsets of up to 3‰, as reported by Sharp et al.(2000), could not be observed. Hence, diagenetic alteration has notshifted dentine values to much lower δ18OP values for these teeth. Al-though, a diagenetic overprint of the original δ18OP and the 87Sr/86Srvalues cannot completely be ruled out, for most of the teeth a significantalteration of the studied tooth enameloid seems unlikely.

However, some diagenetic bias cannot be fully excluded asenameloid/dentine mixtures were analysed due to the small size ofseveral teeth. Some of the sampled localities exhibit features indica-tive for intense post-depositional alteration and recrystallisation(Fig. 4), and were excluded from the subsequent discussion. Toothcrowns of Orthacanthus from the Silbergrund locality show a sul-phide mineralisation in fissures. The fine-clastic host sediment is cov-ered by up to 1000 m of pyroclastics and lavas (Lützner et al., 2007),which might have caused alteration by burial diagenesis. Teeth ofBohemiacanthus from Ortu Mannu, which are derived from a cherty-carbonate lithofacies interfingering with volcaniclastics (Werneburget al., 2007; Ronchi et al., 2008), also show mineralised fissures inthe tooth crowns. Finally, teeth of Bohemiacanthus from Sperbersbachare considered to be altered because of the very large differencein 87Sr/86Sr (0.71046, 0.72522) between two teeth of a single denti-tion. As the δ18OP values of the same teeth do not show a difference,this 87Sr/86Sr offset cannot be attributed to different ambient watermasses of the shark's lifetime habitat.

The single dorsal spine of Orthacanthus from Nýřany shows nei-ther fissures nor structures indicative for diagenetic alteration (ex-cept for an alteration of the central pulpa cavity). However, itsoxygen isotopic composition is depleted by 4–5‰ in comparison tothe CL evaluated enameloid-like outer layer in co-occurringOrthacanthus teeth. This strong deviation is either related to diagene-sis or to metabolic effects, wherefore the isotopic data of this dorsalspine are not further considered.

5.2. Oxygen isotopes of bioapatite from Carboniferous–Permian marinesettings

The bioapatite in shark teeth and spines is frequently used as an ar-chive to reconstruct seawater palaeotemperatures because δ18OP is afunction of temperature and the oxygen isotope composition (δ18OW)of ambient water (Longinelli and Nuti, 1973; Kolodny et al., 1983).

53J. Fischer et al. / Chemical Geology 342 (2013) 44–62

Palaeotemperatures were calculated using the revised phosphate-waterfractionation equation given by Pucéat et al. (2010) instead of the classi-cal equation of Kolodny et al. (1983) due to the use of modern analyticaltechniques and different standards for calibration. A typical seawaterδ18OW of −1‰ for an ice-free and 0‰ for a glacial world (Kolodny andLuz, 1991; Kocsis et al., 2009) has been assumed. This general assumptionfor seawater δ18OW is in accordance with mean seawater differences be-tween late Palaeozoic glacial and interglacial stages documented inconodonts (Joachimski et al., 2006). In contrast, studies of Palaeozoic sea-water δ18O values from the oxygen isotope composition of biogeniccalcite postulate a general long-term increase in δ18O values of about8‰ since the Cambrian (Shemesh et al., 1983; Veizer et al., 1999;Wallmann, 2001; Kasting et al., 2006). However, the biogenic apatite ofconodonts appears to record δ18O and palaeotemperatures of Palaeozoicoceansmore faithfully (Wenzel et al., 2000; Joachimski et al., 2004, 2006,2009). Based on these results significant differences in δ18O of Palaeozoicseawater relative to the modern ocean are not supported by thebioapatite δ18O values, and the typical Cenozoic seawater δ18OW areused here.

The climate of Middle–Late Carboniferous and Early Permiantimes witnessed repeated glaciations and deglaciations of southern-most Gondwana accompanied by glacioeustatic sea-level changes(Roscher and Schneider, 2006; Roscher, 2009; Eros et al., 2012). Thedifferent sedimentary successions studied represent various glacialor interglacial-related wet and dry cycles (Fig. 2). The water temper-atures calculated from shark tooth δ18OP values cover a wide rangefrom 26 to 60 °C for all European localities (Tables 1–2, Supplement).For δ18OP values lower than 17‰ (deglaciation) and 18‰ (glaciation),respectively, the calculated palaeotemperature exceeds the tolerancelimit for modern fishes (38–40 °C; Brock, 1985; Rothschild andMancinelli, 2001). Hence, body temperatures >38 °C of Palaeozoicsharks seem unlikely. Moreover, studies in extant euryhaline sharks(Carlson et al., 2010) as well as in early Jurassic fossil relatives(Dera et al., 2009) indicate conditions of the occupied environmentswith water temperatures in the range of 26–32 °C not exceeding36 °C (Fischer et al., 2012). Therefore, only δ18OP values ≥18‰seem to represent marine water conditions. There is no significantdifference between water temperatures obtained using the marinepalaeotemperature equations of Pucéat et al. (2010) and Kolodnyet al. (1983). Although, temperatures according to Pucéat et al.(2010) are by average 3.5–5 °C higher than those calculatedaccording to Kolodny et al. (1983), both equations result in a multi-tude of seawater temperatures beyond the biological tolerance limit

Fig. 7. Hopane and isoprenoid ratios of sediment extracts allow discrimination of the dClassification diagram modified after Peters et al. (2005).

(Supplement) indicating freshwater environments instead of marineconditions.

This lower limit of 18‰ is also in accordance with the oxygenisotope composition of apatite precipitated from Late Palaeozoic sea-water. Bioapatite of sharks and conodonts from marine deposits wasmeasured for comparison to determine the range in δ18OP of theCarboniferous marine realm (Fig. 4). These data indicate δ18OP valuesfor bioapatite from marine vertebrates between 18.7 and 21.2%VSMOW for the late Early Carboniferous and values of around21.6‰ VSMOW for the early Late Carboniferous (Fig. 4). This is wellin agreement with δ18OP values of late Carboniferous (Moscovian–Gzhelian) conodonts (18.2–21.5‰ VSMOW, Joachimski et al., 2006;values are corrected from the originally used NBS 120c=22.4‰ to21.7‰ VSMOW used here). Independent from the interglacial-glacial range of δ18OP values (1.7‰; Joachimski et al., 2006), all avail-able δ18OP values suggest that apatite precipitated from Carboniferousseawater in the range of average 18 to 22‰ VSMOW. Although for theEarly Permian comparative δ18OP values from marine settings are notavailable, δ18OP values from the ice-free marine Triassic (Sharp et al.,2000; Rigo and Joachimski, 2010; Fischer et al., 2012) show a compa-rable range (17.8–22.3‰ VSMOW after a correction to NBS 120c=21.7‰ VSMOW). Therefore, the reconstructed Carboniferous marineδ18O range appears to be also plausible for the Permian marine glaci-ation and deglaciation periods.

5.3. Oxygen isotopes of bioapatite from Carboniferous–Permian conti-nental basins

The δ18OP values from the basins are mostly depleted by 1–5‰ rel-ative to those of contemporaneous marine settings. This difference inδ18OP is too large to solely reflect changes in temperature (1‰≈4 °C)and, thus, suggest tooth mineralisation in freshwater environments.However, several values from the Puertollano as well as Saar–Nahebasin (Altenkirchen, Blochersberg, Unkenbach, Alsenz) are less de-pleted in 18O (Fig. 4A, Table 1). These elevated δ18OP values seem tobe in accordance with the palaeoenvironmental interpretation ofthese basins as transgressive marine influenced to marginal marine(Soler-Gijón, 1997; Schultze and Soler-Gijón, 2004; Schultze, 2009)contradicting the generally accepted interpretation as fluvial to lacus-trine (Boy, 1989; Stapf, 1989; Wagner, 1989; Colmenero et al., 2002;Schäfer, 2011). The latter view has been, however, recently corrobo-rated by geochemical evidence derived from elemental data andorganic geochemical investigations (for methods see Berner, 2011)

epositional environments of Puertollano, Kounov, Nýřany, and Buxière-les-Mines.

54 J. Fischer et al. / Chemical Geology 342 (2013) 44–62

on a representative sample of a thermally low mature (early oil win-dow) black shale from Puertollano. The contents of total organic car-bon in the black shales of Puertollano amounts to more than 16 wt.%(weight percent of dry sediment), while the relative concentration oftotal sulfur is below 1 wt.%, which is typically observed for lacustrineenvironments (Leventhal, 1995). Furthermore, a hydrogen index of735 mg HC per g Corg suggests a Type I kerogen typically related to la-custrine deposits (Peters et al., 2005, and references cited therein).Also, aliphatic isoprenoids pristane and phytane (Pr/Phy: 2) in combi-nation with low hopane-biomarker ratios (C31-22R-hopane/C30-hopane: 0.12) and low sterane/hopane ratios (C29-sterane/C30-hopane: 0.1) strongly argue for a lacustrine depositional environment(Peters et al., 2005) of the organic matter (Fig. 7).

Altogether, a direct marine influence in both basins is not con-firmed based on the present data base, neither by the sedimentary fa-cies and the organic and isotope geochemistry of the teeth-yieldingstrata nor by the palaeogeographic position of the basins. The only ex-planation to support the interpretation of marine traits for thesesharks and to produce marine-like isotopic values within the teethwould be migration behaviour of the ancient fishes between sea-and freshwater. These teeth likely were mineralised when the sharkswere in marine to brackish environments recording high δ18O signa-tures, and were shed during tooth replacement in the nonmarinebasin environments. Such diadromous behaviour, the migration offishes between fresh and salt water, is well documented by the recentbull shark Carcharhinus leucas (Valenciennes in Müller and Henle,1841), even if latest observations suggest anadromy restricted topregnant females and juveniles (Heupel and Simpfendorfer, 2011;Werry et al., 2011). In fossil sharks solely teeth from the LowerMiocene of the Swiss Molasse basin document similar behaviourdue to unequivocal freshwater signatures in several teeth comparedto other homotaxial teeth from the same locality with marine values(Kocsis et al., 2007).

However, there are further possibilities to generate marine-likeδ18OP values also from freshwater settings without any marine influ-ence. In lacustrine environments under semi-humid conditions thenormally 18O-depleted meteoric water can be enriched in 18O up tovalues equalling or even surpassing seawater values due to stagnationand evaporative enrichment (Talbot, 1990; Holmden et al., 1997;Müller et al., 2006; Tütken et al., 2006; Kohn and Dettman, 2007).Such an increasing pattern in continental interiors is linked to thepresence of a strong monsoonal climate (Dettman et al., 2001). Inthis scenario, the most depleted δ18O values would reflect wet seasonconditions whereas less depleted or even elevated values would rep-resent dry seasons (Fig. 8A). Studies on the evolution of the EarlyPermian Odernheim lake of the Saar–Nahe basin (Müller et al.,2006) also suggest that elevated δ18O values may indicate aclosed-basin lake, while lower δ18O values result from fluvial domi-nated lake phases. Furthermore, shallow water reservoirs such asswamps and ponds undergo more intense evaporation and areenriched in 18O in comparison to open lake waters (Otero et al.,2011). Thus, a difference of up to 5‰ between open freshwatersand nearshore waters, with lower δ18O values in the open waterareas, can be obtained in tropical settings (Fig. 8B).

Some of the elevated shark tooth δ18OP values do not enable aclear differentiation whether the according teeth mineralised infresh- or seawater because they fall within the range of potential ma-rine values. Only very low δ18OP values have clearly characterised an-cient shark habitats as nonmarine so far (Kocsis et al., 2007; Klug etal., 2010; Fischer et al., 2011). Thus, for the sharks with ambiguoustooth δ18OP values the environmental conditions at the time oftooth formation and thus ancient shark behaviour could be eitherinterpreted as euryhaline or stationary freshwater lifestyle in an18O-enriched water body. For refined palaeohydrological reconstruc-tions of the fish habitats, 87Sr/86Sr of the same shark teeth was usedas additional geochemical proxy.

5.4. Strontium and oxygen isotopes as habitat indicators for the sharks

The Late Palaeozoic 87Sr/86Sr record of seawater is characterisedby major fluctuations between 0.7075 and 0.7085 (Fig. 5) caused byvariations in the Sr-flux from continental weathering releasing radio-genic Sr with high 87Sr/86Sr and seafloor basalt alteration releasing Srwith low 87Sr/86Sr (McArthur et al., 2001). Solely the 87Sr/86Sr ratiosof shark teeth from Kalinovskie Vyselki are comparable to thecontemporaneous seawater values (Fig. 5). Teeth from all otherremaining localities are distinctly more radiogenic relative to respec-tive marine 87Sr/86Sr ratios (Fig. 5). Given that freshwater (i.e. riverwater) is generally enriched in 87Sr due to radiogenic Sr inputfrom continental weathering in comparison with coeval seawater(Goldstein and Jacobsen, 1987; Schmitz et al., 1991; Holmden et al.,1997), the high 87Sr/86Sr obtained for the fossil shark teeth from theEuropean basins clearly points to Sr isotope signatures typical fornonmarine environments. This conclusion is supported by the factthat the recorded offset from the contemporaneous strontium seawa-ter curve is at least one magnitude higher than the potential offsetcaused by diagenetic processes (Martin and Scher, 2004).

However, plotting 87Sr/86Sr and δ18OP values of the same sharkteeth yields partly opposing patterns that are not in accordancewith a simple freshwater classification for these specimens (Fig. 9).Since freshwaters and their strontium and oxygen isotope composi-tions are much more influenced by local and regional factors com-pared to the well buffered water masses of the ocean, each basinand each locality may be characterised by individual regional tolocal hydrochemical and climatic conditions.

The isotope data from Kalinovskie Vyselki are plotting within themarine field (Fig. 9A). This is in accordance with previous litho- andbiofacies interpretations of these strata as representing a fully marineenvironment (Ivanov and Ginter, 1996; Duffin and Ivanov, 2008).

In contrast, the isotope values from the localities of the basins ofBourbon l'Archambault, Guardia Pisano, Thuringian Forest, Saale, Bo-hemia and Krkonoše Piedmont plot distinctly outside the marine field(Fig. 9B). δ18OP values from Guardia Pisano that are slightly lowercompared to marine δ18OP values may reflect the vicinity to thePalaeotethys (Fig. 1; Ronchi et al., 2008) leading to a less pronouncedcontinental effect and a minor depletion in 18O (Blisniuk and Stern,2005). The large variability in the 18OP values from the other localitiesseems to be caused by the imprint of local precipitation, river influxand possible groundwater discharge on lake waters. Moreover, therange in δ18OP values from these basins (15.2–18.2‰), which weresituated within tropical latitudes during the late Palaeozoic(Roscher and Schneider, 2006), does not exceed the range of δ18OP

values by fishes from Neogene tropical freshwater environments ofAfrica (17.1–19.3‰; Otero et al., 2011). Furthermore, organic geo-chemical data generated according to the methods of Berner (2011)suggest that sediments from Kounov, Nýřany, and Buxière containvariable mixtures of terrestrial and aquatic organic matter as seenfor example from the hydrogen indices (Peters et al., 2005). Theirnumber ranges from 587 mg HC per g Corg in the sample from Buxièreto about 305 mg HC per g Corg in the Kounov and Nýřany sediments.Low to moderate hopane-biomarker ratios (C31-22R-hopane/C30-hopane: 0.12 to 0.26) in combination with low sterane/hopane ratios(C29-sterane/C30-hopane: 0.03 to 0.1) strongly argue for a fluvial/palustrine or lacustrine environment (Peters et al., 2005), in whichthe organic matter was deposited at Kounov, Nýřany, and Buxière(Fig. 7).

Noticeable is the situation in the Donetsk basin where all samplesfrom Kalinovo are characterised by 87Sr/86Sr ratios close to theexpected marine ratios and by low δ18OP values typical for freshwaterenvironments (Fig. 9C). While near-marine strontium isotope ratiossuggest a certain influence of marine waters, in accordance to previ-ous facies interpretations as nearshore (Eros et al., 2012), the lowδ18OP values document a predominantly freshwater setting similar

Fig. 8. Schematic illustration for possible mechanisms of 18O-enrichment in lacustrine environments and hence elevated δ18OP values in shark teeth from the Late Palaeozoic basin set-tings: (A) strongmonsoonal conditionsmay cause a 18O-enrichment due to stagnation and intense evaporation during dry seasons, while input of 18O-depletedwater in the course of thewet seasons via the precipitation and strong fluvial input into the water reservoir may cause a 18O-decrease (Dettman et al., 2001); and (B) variation in δ18O values up to 5‰ betweendifferent water masses (open lake waters, restricted littoral and swamps, fluvial input) due to stagnation, surface/volume ratio and evaporation (Otero et al., 2011).

55J. Fischer et al. / Chemical Geology 342 (2013) 44–62

to modern estuarine conditions. In contrast, values from the youngerLuganskoje limestone with low δ18OP values and relatively high 87Sr/86Sr ratios are similar to the range of the other Mid European basins(Fig. 9B, C). Here, it indicates tooth formation under freshwater con-ditions as previously proposed (Schneider et al., 1992).

Data from Götzenhain show similarities with Kalinovo inasmuch as87Sr/86Sr ratios are close to the contemporaneous strontium seawaterrange while δ18OP values are depleted in 18O by 3–5‰ relative toexpected marine signals (Fig. 9D). Since the palaeogeographic settingof the Sprendlinger Horst does not support a marginal marine position(McCann et al., 2008), seawater influx cannot be put forward to explainthe low, seawater-like 87Sr/86Sr. Instead, these values likely reflectlow 87Sr/86Sr of the bedrock weathering in the drainage area. TheSprendlinger Horst is part of the Spessart Crystalline and thus theMid-German Crystalline High, consisting of intermediate to alkalinemagmatites with typically low 87Sr/86Sr ratios (0.7077; Dombrowskiet al., 1995). Weathering of these silicate rocks served as a source for

the Permian sediments (Okrusch et al., 2000) supporting the idea ofbedrock induced low 87Sr/86Sr ratios instead of near marine signatures.

The most contrasting patterns are recognisable in the isotopevalues from localities of the Saar–Nahe basin as well as thePuertollano basin. While all 87Sr/86Sr ratios are more radiogenic incomparison to seawater ratios, several δ18OP values are close to orwithin the proposed marine δ18O range (Fig. 9E, F). Such a patternof Sr and O isotope composition cannot be explained by diadromousbehaviour of the accorded sharks. The evaporative enrichment in18O of the ambient freshwater in which the shark teeth mineralisedis more likely to explain these marine-like δ18OP values andfreshwater-like 87Sr/86Sr ratios.

The elevated δ18OP values in the Saar–Nahe basin may reflect thespecific drainage situation of the basin. The fauna is characterised bya variety of endemic species such as Orthacanthus (Lebachacanthus)senckenbergianus Fritsch, 1889, Rhizodopis hanbuchi Schultze andHeidtke, 1993, Archegosaurus decheni Goldfuss, 1847, and different

Fig. 9. δ18OP vs 87Sr/86Sr plot of shark teeth displaying the environmental conditions (i.e. the isotopic composition of the ambient water in the shark habitat) at the time of toothformation for the single localities. The horizontal grey bar represents the range of the seawater strontium isotopic composition for the according stratigraphic age of each locality(Denison et al., 1994; Veizer et al., 1999; Korte et al., 2006) while the vertical grey bar shows the proposed marine δ18O range (see text for more details). The intersection betweenboth bars characterises bioapatite values expected for unequivocal fully marine conditions. A — Moscow Syneclise (Serpukhovian), B — basins of Central Europe (Gzhelian–Sakmarian), C — Donetsk basin (Moscovian–Gzhelian), D — Sprendlinger Horst (Sakmarian), E — Saar–Nahe basin (Gzhelian–Artinskian), and F — Puertollano basin (Gzhelian).

56 J. Fischer et al. / Chemical Geology 342 (2013) 44–62

branchiosaurs (Werneburg and Schneider, 2006). This fauna pointsto an endorheic basin with rare ephemeral external drainage duringmost of the Late Carboniferous and Early Permian (Boy andSchindler, 2000).

The Altenkirchen packstone of the Saar–Nahe basin, with δ18OP

values close to the marine range (Fig. 4), were deposited in a smalland shallow lake under semi-humid climatic conditions (Boy andSchindler, 2000; Schindler, 2007). Such hydrodynamic and climaticconditions should result in high δ18OP values of fishes living in such

a water body according to Otero et al. (2011) (Fig. 9E). The Alsenzand Unkenbach localities of the Raumbach and Breitenheim lakehorizons, respectively, are representative of basin-wide lakes inthe Saar–Nahe basin, both consisting of 2.5 m laminated (varved)claystones with intercalations of marls and pyroclastics. Both locali-ties show elevated δ18OP values plotting close to the lower range ofmarine environments. The lamination (varvites) indicates the preva-lence of a monsoonal climate (Boy, 2003; Schindler, 2007) during themiddle Asselian dry phase (Roscher and Schneider, 2006), which

57J. Fischer et al. / Chemical Geology 342 (2013) 44–62

could have lead together with endorheic conditions to elevated δ18OP

values. The Sobernheim sharks, instead, lived in a small lake con-nected to a river course in a fluvial dominated depositional environ-ment (Boy, 2003). The low δ18OP value seems to be the result ofincreased riverine input of 18O-depleted meteoric waters (Fig. 9E). Ifthe low δ18OP values from the Odenbach lake of Blochersberg repre-sent a wet season or are the result of more depleted open lake watersremains, however, speculative.

High δ18OP values from teeth of the Puertollano black shales(Fig. 9F) seem to be caused by higher evaporation in a stratifiedlake due to warm and seasonally dry climate conditions and sufficientresidence time of the water in the basin. Such effects are likewiseapplicable for some other Mid European lakes though not to thesame extent as for the Saar–Nahe and Puertollano basin, at least notpreserved in the here investigated teeth.

No δ18OP signatures pointing to glacier water influence (b10‰;Mook, 2000) were detected in the present samples as it should beassumed by Carboniferous and Permian basins situated in elevationsin excess of 2000 to 5000 m (Becq-Giraudon et al., 1996; Boy andSchindler, 2000). On the contrary, the studied basins were situatedin an altitude ranging from close to the sea-level to a low-mountainrange topography (Schneider et al., 2005). This is further supportedby the absence of any topography-related differentiations in thefloras (Kerp, 2000; Opluštil et al., 2005; Bashforth et al., 2011), andcalculations of the denudation rate of the Variscides (Roscher andSchneider, 2006; Pešek and Martínek, 2012).

Altogether, combined δ18OP and 87Sr/86Sr analyses of shark teethfrom the different Late Carboniferous to Early Permian Europeancontinental basins do not support the often proposed marine traitsfor these sharks. No convincing marine isotope signatures could bedetected, wherefore the bioapatite mineralisation of the investigatedshark teeth most likely took place in freshwater environments.

5.5. Palaeoecologic implications for the sharks from the Late Palaeozoicbasins

Extant sharks from subtropical and cold seawater show δ18OP

variability in the range of up to 1.1‰ within a single dentition, of upto 1.2‰ for intra-species variation, and of up to 2.5‰ for interspeciesvariation due to individual habitats with different temperatures in thewater column (Vennemann et al., 2001). For fossil shark taxa, it has tobe tested whether the δ18OP range is within the ‘normal’ biologicalvariation. Assuming that fossil sharks had the same intraspeciesδ18OP variability like extant relatives the mean standard deviation ofsingle species at most localities is within this range (0.1–0.6‰;Table 2). Several taxa at single localities, however, show a larger var-iability of 1.4–2.2‰ (Orthacanthus/Puertollano, Lissodus/Moosbach,Triodus/Blochersberg, Bohemiacanthus/Götzenhain; Table 2) clearlyexceeding that recorded for modern sharks. This may to some degreerepresent the effect of recurring stagnation and evaporation of lakewaters as discussed before. Alternatively, shark movements between18O-depleted fluvial affected freshwater environments or open lake

Table 3Mean δ18OP values (in VSMOW) and 87Sr/86Sr ratios of apatite from different shark spines. Cin Fig. 1.Palaeotemperature estimates TW are based on the equations of Pucéat et al. (2010).

Species Material Locality Meanδ18OP

Orthacanthus Dorsal spine Kounov, 9, CZE 17.3Turnovichthys Fin spine Krsmol, 10, CZE 17.6Orthacanthus Dorsal spine Buxiéres, 2, FRA 16.6Lissodus Fin spine Buxiéres, 2, FRA 16.8Lissodus Fin spine Buxiéres, 2, FRA 16.6Lissodus Fin spine Buxiéres, 2, FRA 15.6Lissodus Fin spine Guardia Pisano, 3, ITA 17.6

areas and 18O-enriched waters encountered in nearshore to restrictedlake bay settings (Fig. 8B; Otero et al., 2011) may also contribute tothe observed higher variability. Movements of up to a few km werelikely within the typical home range, as seen in recent relatives,while longer distances suggest periodic home range shifts, possiblydue to prey shortage, disturbance, or search for a mate (Whitneyet al., 2012). The detection of ontogenetic shifts in the habitat useby Palaeozoic and Triassic xenacanthiformes and hybodontids in thenonmarine realm suggest pronounced periodic movements to specif-ic nursery areas and back to the normal life habitats more distantfrom the nursery, at least by gravid females (Maisey, 1989;Schneider and Reichel, 1989; Fischer et al., 2011).

In spines of Lissodus, Turnovichthys and Orthacanthus δ18OP varia-tions between single layers exhibit a variability of 0.2–1.2‰ (n=25), while variability between different Lissodus spines from GuardiaPisano is of 0.6‰ (n=14) (Tables 2–3, Supplement) congruent to theintra-specific range in δ18OP of the teeth (Table 2). Thereby, Lissodusand Turnovichthys show less variation between single layers(0.2–0.4‰, n=12) while Orthacanthus spines preserved variationsup to 1‰ (n=13). More pronounced migration behaviour inOrthacanthus is, however, not supported neither by δ18OP variationsin associated teeth nor by the small number of spines investigatedso far. Furthermore, neither spine δ18OP values nor 87Sr/86Sr ratiosprovide indication for tidal conditions as proposed on the basis ofregular alteration of growth layers for Orthacanthus from the LateCarboniferous of Robinson, Kansas (Soler-Gijón, 1999). The observedvariations in δ18O values may simply reflect seasonal growth causedby a seasonal climate and/or reproduction cycles. All shark toothisotope data from Europe in this study support shark migrations infreshwater environments only.

For the investigated shark taxa freshwater habitats have beeninferred from a variety of facies patterns of shark-yielding strata inMiddle Europe (Schneider and Zajíc, 1994; Boy and Schindler,2000). Thus, Orthacanthus generally occurred in large river systemsand extended perennial lakes. Bohemiacanthus preferentially lived inthe littoral and pelagial realm of mostly eutrophic lakes. Xenacanthusseemed to have been a euryoecious form living in rivers and oligotro-phic to eutrophic lakes. Triodus (sensu stricto — see Schneider, 1996)occurred rarely in the European realm in eutrophic lakes andfluvial-lacustrine habitats. The littoral of large oligotrophic and eutro-phic lakes were the assumed habitats for the hybodontid Lissodus andthe sphenacanthid Sphenacanthus (Schneider, 1986; Gebhardt, 1988;Boy and Schindler, 2000). Under the assumption that species-specificoxygen isotope fractionation in fossil sharks are negligible as inmodern relatives (Vennemann et al., 2001), different δ18OP values ofco-site taxa (Fig. 4, Table 2) could be ascribed to varying habitatclaims. Nevertheless, such an interpretation is in part complicatedby shark migration or the small number of studied teeth. Normally,at least 6–10 teeth per species are required to obtain an accurateisotopic resolution (Clementz and Koch, 2001; Kohn and Dettman,2007). In this study some taxa are represented by only 1–3 samplesper site (Table 2), and when a numerically sufficient data base is

ZE, Czech Republic; FRA, France; and ITA, Italy. Locality numbers refer to basin numbers

Std.(1σ)

n Mean87Sr/86Sr

n TW (°C)

0.5 6 0.71029 2 41.90.2 3 0.70998 1 40.60.6 7 – – 40.60.1 2 0.71070 1 39.80.1 4 0.71058 1 40.80.2 3 0.71077 1 44.90.3 14 0.71036 2 36.4

58 J. Fischer et al. / Chemical Geology 342 (2013) 44–62

available as in Buxière, no significant differences can be recognised(Fig. 4B; Table 2). It is, therefore, not evident from the available iso-tope values if apparent differences between co-site taxa (Puertollano,Dobis, Blochersberg; Fig. 4B) reflect differences in the habitat claimsor simply represent artefacts of the low number of teeth investigatedfrom each site due to sample bias. Further investigations of largernumbers of teeth from co-site taxa are required.

Carpenter et al. (2011) claimed a salinity tolerance of xen-acanthids like Xenacanthus and Triodus (sensu lato — the figuredteeth [Carpenter et al., 2011: Fig. 7K–L] belongs sensu stricto toBohemiacanthus Schneider and Zajíc, 1994) to near-stenohaline con-ditions, while solely Orthacanthus is expected to tolerate brackishwater environments. These salinity tolerance estimates were derivedfrom facies interpretations in the Permian of North America (Sander,1989; Johnson, 1999). The geochemical results of this study togetherwith the lithofacies and palaeogeography recorded for the Palaeozoicbasins of Europe do not support this assumption. The oxygen isotopiccomposition of shark-teeth from the Variscan basins of Europeclearly demonstrate that xenacanthiform but also hybodontid andsphenacanthid taxa had no salinity restrictions to near marine condi-tions affirming the general interpretation of a variety of Palaeozoicshark taxa as obligate freshwater fishes (Masson and Rust, 1983;Schneider and Zajíc, 1994; Schneider, 1996; Dick, 1998; Kriwetet al., 2008; Fischer et al., 2010). Existing isotopic variations in thefossil shark teeth are related either to the local hydrology or to thetype of habitat.

This conclusion does not automatically exclude the euryhalinecapability and facultative/obligate migrations between marine andnonmarine habitats of xenacanthiform, sphenacantid and hybodontidsharks in other palaeogeographic regions as in Nova Scotia, MazonCreek or Texas (Calder, 1998; Johnson, 1999; Janvier, 2007;Schultze, 2009; Carpenter et al., 2011). The depositional environ-ments as well as faunal associations of Carboniferous to Early Permianbasins in North America were intensely influenced by repeatedtransgressive/regressive cycles (Belt et al., 2011), and thus werecompletely different from those of post-Moscovian basins in Europe(Schneider and Romer, 2010). The latter were located hundreds ofkilometres away from any coast (Fig. 1; Opluštil and Pešek, 1998;Roscher and Schneider, 2006; Schneider and Romer, 2010). In theEuropean realm, the adaption of sharks to fluvial-lacustrine habitatsstarted latest in the Mississippian (Late Viséan) as indicated by amass-occurrence of xenacanthid and hybodontid egg capsules in flu-vial sand- and siltstones of an alluvial plain of the Hainichen basin,Germany (Schneider et al., 2005).

6. Conclusions and perspectives

In total, 179 samples of teeth and spines of different Late Carbonif-erous and Early Permian shark taxa from several European basinswere analysed for their oxygen and, partly, strontium isotope compo-sition to infer the hydrochemistry of their ambient water, and contrib-ute to the controversial question of their ancient palaeoecologyregarding an obligate freshwater or euryhaline diadromous lifestyle.The tooth δ18OP valuesmeasured in this study provide strong evidencefor an obligate freshwater lifestyle for the investigated sharks. Al-though the δ18OP values at some sites are in the order of the estimatedmarine range, the nonmarine 87Sr/86Sr ratios clearly indicate that theaquatic environments in which the sharks formed their teeth wereinfluenced bymeteoric waters enriched in 18O by evaporation. This in-terpretation is concordant with current Late Palaeozoic climaticmodelling results (Roscher and Schneider, 2006). Furthermore, theisotopic analysis of the non-replacement shark spines, reflectinglife-long environmental conditions, does not show different resultsthan the teeth. Therefore, the presented geochemical data supportan obligate freshwater lifestyle for the hybodontid, xenacanthiform,

and sphenacanthid sharks in the European basins. Euryhaline adapta-tion cannot be confirmed.

The inter-tooth δ18OP variation for most localities exceeds theintraspecies δ18OP range observed for modern sharks. This is inter-preted to reflect either migrations of the sharks between differentfreshwater habitats such as more restricted areas in lakes and fluvialinfluenced environments in the course of foraging or reproduction oralso seasonal changes in lake water oxygen isotopy depending onprecipitation and evaporation. However, based on the oxygen isotopesignatures no systematic habitat differences could be determined forthe different shark taxa. Thus, further geochemical studies on largernumbers of both fossil and recent shark teeth, as well as articulateddentitions, are required to study the migration behaviour of sharkswith higher temporal resolution. Such analyses will help to determinepatterns of habitat change and migrational behaviour and to clarify towhat extent inter- and intraspecies variations of δ18OP values inextant sharks are applicable to their fossil extinct sister groups.

Acknowledgements

We would like to thank B. Gaitzsch (TU Freiberg), R. Soler-Gijón(Museum für Naturkunde Berlin), N. Klein (University Bonn), B. Ekrt(National Museum Prague), S. Štamberg (Museum of EasternBohemia Hradec Králové), T. Schindler (Büro PSG Spabrücken), R.Werneburg (Naturhistorisches Museum Schleusingen), M. Wuttke(Generaldirektion Kulturelles Erbe Mainz), N. Udovichenko (NationalUniversity Lugansk), A. Ivanov (St. Petersburg University), K.Krätschmer (Odernheim), and J-M. Pouillon (Nivolas-Vermelle) forgenerously providing tooth material for this study. Special thanksgot to S. Sekora (TU Freiberg) for laboratory work, J.M. Wargenau(TU Freiberg) for assistance in strontium isotope measurement, andD. Dettmar (Bochum) for the preparation of thin sections for CL mea-surements. S. Evers (Munich) is acknowledged for the meticulousseparation of enameloid and dentine of some shark teeth. Shark andplant inlets were made by F. Spindler (TU Freiberg). We appreciateconstructive reviews of two unknown reviewers as well as linguisticassistance of A.J. Lerner (Albuquerque). This research was financedby the German Research Foundation (DFG-SCHN 408/14-1, and par-tially DFG-TU 148/2-1).

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.chemgeo.2013.01.022.

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