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New Triassic stem selachimorphs (Chondrichthyes,Elasmobranchii) and their bearing on the evolution ofdental enameloid in NeoselachiiPlamen S. Andreev a & Gilles Cuny ba Earth Sciences Department, University of Birmingham, Birmingham, B15 2TT, UnitedKingdomb Natural History Museum of Denmark, Øster Voldgade, 5-7, 1350, København K, Denmark

Version of record first published: 28 Feb 2012.

To cite this article: Plamen S. Andreev & Gilles Cuny (2012): New Triassic stem selachimorphs (Chondrichthyes,Elasmobranchii) and their bearing on the evolution of dental enameloid in Neoselachii, Journal of Vertebrate Paleontology,32:2, 255-266

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Journal of Vertebrate Paleontology 32(2):255–266, March 2012© 2012 by the Society of Vertebrate Paleontology

ARTICLE

NEW TRIASSIC STEM SELACHIMORPHS (CHONDRICHTHYES, ELASMOBRANCHII) ANDTHEIR BEARING ON THE EVOLUTION OF DENTAL ENAMELOID IN NEOSELACHII

PLAMEN S. ANDREEV*,1 and GILLES CUNY2

1Earth Sciences Department, University of Birmingham, Birmingham B15 2TT, United Kingdom, pxa012@bham.ac.uk;2Natural History Museum of Denmark, Øster Voldgade 5-7, 1350 København K, Denmark, gilles@snm.ku.dk

ABSTRACT—This study identifies three new neoselachian tooth taxa from the Middle and Upper Triassic. On the basis ofmorphological and histological characters, Rhomaleodus budurovi, nov. gen. et sp. (Anisian of Bulgaria), is resolved as stemselachimorph, with an additional specimen from the same stratigraphic level assigned to Synechodus sp. Selachimorph gradeof enameloid microstructural organization (crystalline bundles) was also identified during examination of the dental tissuesof “Polyacrodus” holwellensis (Rhaetian of England), necessitating its transfer to the new genus Duffinselache. The presentdata reveal several levels of increasing architectural complexity in the arrangement of the enameloid crystalline bundles ofstem selachimorphs, which are argued to convey a phylogenetic signal that can be used to establish relationships within thegroup. It is suggested that the evolution of the hypermineralized enameloid cover of neoselachian teeth progressed from aplesiomorphic single crystalline state, through amalgamation of individual crystals into loosely defined bundles (marking theappearance of Selachimorpha), and their subsequent differentiation into a highly ordered parallel bundles, followed by thedevelopment of an inner layer of haphazardly oriented bundles. The superficial shiny-layered enameloid of Neoselachii isinterpreted as remnant of a much reduced single crystalline layer.

INTRODUCTION

The Neoselachii unites crown elasmobranchs whose mono-phyly has been strongly supported through a series of phylo-genetic studies (to name a few: Compagno, 1977; Thies, 1983;Maisey, 1984; Shirai, 1992; de Carvalho, 1996; Maisey et al.,2004). The intergroup relationships within the clade, on the otherhand, have been a matter of contention, especially when re-garding the systematic position of Batomorphii (sensu Cappetta,1987) relative to the rest the neoselachians (united under Selachi-morpha Nelson, 1984, sensu Velez-Zuazo and Agnarsson, 2011).On the basis of morphological characters alone, batomorphs re-peatedly appear nested within selachimorphs (Thies, 1983; Thiesand Reif, 1985; de Carvalho, 1996; Shirai, 1992, 1996) or have un-resolved status at the base of the neoselachian phylogenetic tree(Compagno, 1977; Maisey, 1984). The molecular phylogenies,though, clearly suggest a sister-group relationship between Bato-morphii and Selachimorpha (Douady et al., 2003; Maisey et al.,2004; Naylor et al., 2005; Velez-Zuazo and Agnarsson, 2011),and as commented by Maisey et al. (2004), this discrepancywith the anatomical analyses might be due to employment ofhomoplasious characters in the latter, which leads to allyingtaxa with similar ecological specializations (batomorphs withsqualomorph sharks).

The fossil evidence indicates that the teeth of some of thestratigraphically oldest neoselachians (the Carboniferous–Permian genus Cooleyella Gunnell, 1933) possess only a singlecrystalline enameloid (SCE) cover (G.C., pers. observ.), whichwas retained in batomorphs (see Discussion for details), andopposes previous claims considering bundled enameloid as earlyneoselachian evolutionary development (Reif, 1977; Thies, 1983;Thies and Reif, 1985). As the vast majority of the Palaeozoic andEarly Mesozoic neoselachian skeletal remains are representedby isolated teeth, there is an increasing reliance on enameloid

*Corresponding author.

microstructural organization to distinguish between high-rankedtaxa within the group. This is of particular relevance to themost diverse early neoselachian fauna known to date, whichis of Triassic age. Presently, it includes nine validly recognizedgenera, with only a small number of them (Synechodus, Mu-crovenator, Rhomphaiodon) being assigned to a particular order(all three included within Synechodontiformes by Klug, 2010).The uncertain state of Triassic neoselachian systematics has beendictated by failure to establish diagnostic dental characters forstem members of the group.

In the current study, we try to address some of these issuesby describing a new genus and a new species of stem selachi-morphs from the Anisian of Bulgaria, accompanied by a revisionof “Polyacrodus” holwellensis (Duffin, 1998b), which is trans-ferred from Hybodontiformes to Neoselachii. These data help todifferentiate several grades of structural complexity of bundledenameloid, which are argued here to be characteristic for indi-vidual lineages of stem neoselachians.

MATERIALS AND METHODS

All material investigated in the present work consists ofisolated teeth. Specimens of Rhomaleodus budurovi, nov. gen. etsp. (BU5239, BU5240, BU5241, BU5242, BU5243, BU5244), andSynechodus sp. (BU5245) formed part of Prof. Kiril Budurov’sextensive microvertebrate collection acquired during the courseof his work on the Triassic conodont biostratigraphy of theTethys province (Budurov and Stefanov, 1972, 1973, 1974, 1975;Budurov, 1977; Sudar and Budurov, 1979; Budurov, 1980).The above-mentioned material comes from three separatesamples (93–3 quarry 1 km Bg P+K [BU5239, BU5240, BU5241,BU5242]; 98 7-f quarry 1 km WyBg P+1K [BU5243, BU5244];81 GII P+K [BU5245]) obtained from the sections “Quarries”(first two samples) and “Bobuk dol” (third sample), located inthe vicinity of Belogradchik (Vidin District, Bulgaria; Fig. 1);

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FIGURE 1. A, location of the town of Belogradchik and the surround-ing study area depicted as black rectangle on the geographical map ofBulgaria; B, geological map (modified from Angelov et al., 2006) of theregion demarcated in A, showing the locations of the two outcrops thathave yielded the presently examined Middle Triassic neoselachian fauna.

refer to Chatalov and Doneva (2009) for sedimentologicaldescription, and Stefanov (1977) and Muttoni et al. (2000) fordetails about the litho-, magneto-, and biostratigraphy of thestrata cropping out at the sites. The information accompanyingthe specimens allowed tracing their provenance to the Anisiansediments of the Babino Formation (Tronkov, 1973), belongingto the Balkanide-type Middle Triassic sequences of the IskarCarbonate Group (Tronkov, 1981).

Chondrichthyan microremains from the Babino Formationhave been reported in relation to their stratigraphical sig-nificance (Stefanov, 1977), but never properly figured nordescribed.

Prior to imaging, BU5242, BU5243, and BU5245 were surface-etched 5 seconds in 3.4% HCl for the purpose of revealing the mi-crostructural architecture of the enameloid layer. A 300 A thickcoat of gold-palladium alloy was subsequently applied to all stud-ied teeth of Rhomaleodus budurovi, nov. gen. et sp., and Syne-chodus sp., which were photographed using the FEI Inspect scan-ning electron microscope (SEM) of the Natural History Museumof Denmark with acceleration voltage of 10 and 15 kV, the 515Philips SEM of the Central Laboratory of Mineralogy and Crys-tallography (Bulgarian Academy of Sciences) with accelerationvoltage of 22 kV, and the JEOL JSM-5300LV SEM of the Schoolof Dentistry at the College of Medical and Dental Sciences (Uni-versity of Birmingham), with acceleration voltage of 20 kV. Thespecimens assigned to Rhomaleodus budurovi, nov. gen. et sp.,

and Synechodus sp. are deposited in the type collection of theLapworth Museum of Geology (University of Birmingham).

Specimens of “Polyacrodus” holwellensis studied by one of us(G.C.) between 1997 and 1999 belong to the Moore Collectionof the Bath Royal Literary and Scientific Institution (lot num-ber BRLSI M0067). The specimens were found in the Late Tri-assic fissure fillings of Holwell in Somerset (England). We referto Duffin (1998a) for more details about the origin and historyof this collection. A total of four teeth were prepared for enam-eloid microstructure study, two of which are figured in the presentwork. The first one was surface-etched in 10% HCl for 5, 5, 30,and 30 seconds. After each etching, the tooth was coated with apalladium-gold alloy and pictures of the surface of the enameloidwere taken using a Cambridge Stereoscan 250MK3 scanning elec-tron microscope with an acceleration voltage of 25 kV. The sec-ond tooth was embedded in resin and cut through the middlealong its labio-lingual axis. The section was then polished man-ually using a number 400 silicon carbide waterproof paper andetched 5 seconds in 10%. The specimen was subsequently coatedand photographed with SEM.

Terminology

The descriptive terms of neoselachian dental morphology fol-low with slight modification (lateral cusplet instead of lateralcusp) those introduced by Johns et al. (1997).

SYSTEMATIC PALEONTOLOGY

Superclass CHONDRICHTHYES Huxley, 1880Class ELASMOBRANCHII Bonaparte, 1838

Cohort EUSELACHII Hay, 1902Subcohort NEOSELACHII Compagno, 1977

Superorder SELACHIMORPHA Nelson, 1984Order SYNECHODONTIFORMES Duffin and Ward, 1993

Family PALAEOSPINACIDAE Regan, 1906Genus SYNECHODUS Woodward, 1880

Type Species—Synechodus dubrisiensis (Mackie, 1863), fromthe Cenomanian (Upper Cretaceous) of England.

Remarks—The genus Synechodus was introduced by Wood-ward (1888) for a set of articulated elasmobranch Meckeliancartilages with preserved in situ dentition from the Upper Creta-ceous Chalk of Sussex (England). Previously, similar teeth withassociated jaw cartilages have been referred by Mackie (1863)to Hybodus dubrisiensis, but Woodward (1888) justified theerection of a new taxon by emphasizing the specialized natureof the heterodont clutching-type dentition revealed in the newspecimen.

More recently, Duffin and Ward (1993) reaffirmed the va-lidity of the genus by defining the following diagnostic den-tal characters: lateral cusplets confluent with one another andthe main cusp, overhang of the tooth neck by the labial crownface, and strongly diminishing or completely missing cusps inposterior tooth rows. On these grounds, they assigned to Syne-chodus only one Triassic species, S. rhaeticus Duffin, 1981, knownfrom the Rhaetian of England (Duffin, 1982, 1998b). In thefollowing years, an increasing number of Permo–Triassic toothspecies, often of contrasting dental morphologies, have been as-signed to this genus. These include S. antiquus (Ivanov, 2005),the stratigraphically oldest (Sakmarian–Artinskian) member ofSynechodontiformes, and the Triassic species S. triangulatus, S.sp. (Yamagishi, 2004); S. sp. (Ivanov and Klets, 2007); S. volati-cus, S. multinodosus, S. incrementum, S. sp. 1, S. sp. 2 (Johns et al.,1997).

In her phylogenetic study of Synechodontiformes, Klug (2010)regarded pre-Jurassic Synechodus species as taxa with un-certain systematic position compared to the better-definedpost-Jurassic forms, known in some instances from partial

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FIGURE 2. Fragmentary tooth (BU5245) of Synechodus sp. from the Babino Formation, Anisian of Bulgaria. Surface-etched 5 seconds in 3.4%HCl. SEM micrographs. A, labial view; B, lingual view; C, mesial? view; D, occlusal view. Scale bars equal 200 µm.

(Woodward, 1888, 1911; Maisey, 1985; Klug, 2009) or com-plete skeletons (Leidner and Thies, 1999; Kriwet and Klug,2004). The character matrix used by Klug (2010) identifies sev-eral key features of Permo–Triassic Synechodus teeth: clutching-or grinding-type dentition, triple-layered enameloid structure,pseudo-polyaulacorhize root vascularization, baso-labial root de-pression, and lateral cusplets. It became apparent in the presentstudy, though, that only one species (S. multinodosus) can con-fidently be recognized under these criteria, because some pre-Jurassic taxa have not been examined histologically, whereas oth-ers lack tangled-bundled enameloid (TBE) or can possess anaula-corhize vascularization. Here we present a modified list of dentalcharacters that are considered to apply to Synechodus, althoughonly full revision of the genus can resolve the affinities of pre-Jurassic forms affiliated with it. These include: crown cusps notdistinctly separated from each other, crown base overhangingthe crown-root junction, presence of baso-labial root concavity,pseudo-polyaulacorhize type of root vascularization occasion-ally changing to anaulacorhize in lateral or posterior tooth files,clutching-type dentition, gradual decrease of tooth height to-ward the commissure, enameloid layer containing shiny-layeredenameloid (SLE), and well-structured parallel-bundled enam-eloid (PBE) with developed thick radial bundles (sensu Guinotand Cappetta, 2011).

SYNECHODUS sp.(Figs. 2, 6D)

Material—A single, partially preserved tooth (BU5245) com-prised of a main cusp and a flanking mesial crown shoulder sup-ported by the root. The specimen was treated with 3.4% HCl for5 seconds, with no significant removal of the mineralized tissuescaused by the procedure.

Locality—Bobuk dol Section (Stefanov, 1977; Muttoni, et al.,2000), situated 3.5 km north of the town of Belogradchik (VidinProvince, NW Bulgaria), near the village of Granitovo (Fig. 1).

Occurrence—Babino Formation, Paragondolella bifurcataConodont Zone (Budurov and Stefanov, 1972), Illyrian Substageof the Anisian Stage (Middle Triassic).

Description

Morphology—The specimen attains its greatest dimension of0.8 mm along the mesio-distal axis; the actual size of the toothmust have exceeded 1 mm, because the entire distal portion of thecrown is missing. BU5245 achieves maximum height of 0.6 mm atthe apex of the main cusp. A ratio of 1.27:1 is measured betweenthe lingual root face and crown height, but labially these propor-tions change to 0.9:1 because of the reduced root thickness.

The preserved part of the crown consists of a conical main cuspconfluent with an elongate mesial shoulder region. The cusp has a

noticeable lingual curvature and slightly symmetrical appearancedue to its moderate distal inclination (Fig. 2B, C). It displays ablunt apical region caused by abrasion of the enameloid coverthat reveals the internal organization of the crown’s dental tissues(Fig. 2B). The labial crown surface possesses flat to moderatelyconcave profile at the base of the cusp, in contrast to the bulgedlingual face.

The labial crown face is ascended by multiple ridges that tendto converge towards the tooth apex (Fig. 2A, D). Those devel-oped on the crown shoulder never attain its apical extremity, fad-ing out at half distance. In comparison, all of the more linearand much shorter lingual vertical ridges reach the occlusal crest(Fig. 2B). The crest itself shows strong displacement in lingualdirection, being continuous throughout the observable portionof the tooth (Fig. 2D). Midway along the crown shoulder thereis a pronounced hump, interpreted as incipient lateral cusplet.The shoulder and the cusplet are strongly labio-lingually com-pressed and clearly set apart from the more robust crown base.The latter is marked by the circumferential rim of the longitu-dinal shoulder line (LSL), which reaches the vertical ornamen-tation. Another notable feature in the lower crown region is thestrong bifurcation of the ridges running on both sides of the maincusp.

BU5245 demonstrates root extension beyond the labial and lin-gual limits of the crown (Fig. 2D). The moderately developed lin-gual torus thickens at the mid-region of the tooth, where there isconcentration of foramina (Fig. 2B) of varying diameter (26–100µm) and shape (circular to elliptical); additionally, a single fora-men is present close to the thinner mesial root extremity. Thesefeatures are characteristic for the lower lingual root face, whichpasses apically into a much constricted neck region. This upperroot face attains 40% of the height of the lingual torus and is de-void of vascular openings or any kind of ornament.

The presence of a deep basal concavity causes the labial rootface to exhibit a low-arching profile (Fig. 2A). The latter in-creases gradually in height and thickness towards the midsectionof the tooth, following the maximal apical extension of the crownat the region of the main cusp. A longitudinal furrow divides theroot into unequal upper and lower faces. They are missing vascu-lar canal openings except for two small foramina midway up ofthe lower root face, contrasting with the more vascularized lin-gual torus.

The basal outline of the root is elongate, with a rounded mesialextremity. The lingual half of the basal surface is flat and feature-less, whereas the labial one is characterized by a deep depressionmarked by labio-lingually extended oval canal openings (140–200µm in diameter). The vascularization type is considered to beanaulacorhize with concave baso-labial surface (see Johns et al.,1997:fig. 7B), on grounds that no clear grooves are detected onthe root base.

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Histology—The tooth crown consists of orthodentine coveredby a hypermineralized enameloid layer (see Fig. 6D). The enam-eloid microstructure was investigated on the worn out apical por-tion of the main cusp. It reveals the presence of a superficial SLElayer with thickness varying from 2.5 µm at the inter-ridge spacesto ∼5 µm within the ridges. The individual rod-shaped crystal-lites that constitute this layer have no preferential orientationand measure ∼2 µm long. Situated beneath the SLE is a highlystructured PBE. The extent of this layer cannot be accuratelydetermined due to a lack of available specimens for sectioning.What can be estimated from the studied fractured surface is thatit reaches at least 30 µm in thickness in this part of the crown. Thebundles of the PBE are organized into distinct radial and parallelsets. The radial component is strongly developed in the externalportion of the tissue (bundle thickness approaching 4 µm), buttends to fade out towards the interior of the tissue. These bundlesare evenly spaced at 4-µm intervals, occupied by the orthogonalsurface parallel bundles. The deeper portions of the enameloidlayer are almost entirely masked by a diagenetic crust, which pre-vents the identification of a possible TBE in this region.

Comparison

BU5245 most closely resembles Synechodus sp. described byYamagishi (2004) from the Olenekian–Anisian of Japan. It showssimilar distally inclined main cusp with vertical ridges convergingtowards its apex, labio-lingually compressed crown shoulders, ar-cuate root profile, uneven distribution of foramina on the lingualroot face, and anaulacorhize vascularization. The only notabledifference is seen in the crown shoulder region, where BU5245possesses a single lateral cusplet contrasting with the multiplecusplets developed on the mesial shoulder in posterolateral teethof Synechodus sp. (Yamagishi, 2004). BU5245 is left in opennomenclature because no additional material is available to jus-tify the erection of a new species.

Order and Family incertae sedisGenus RHOMALEODUS, nov. gen.

Etymology—From ‘Rhomaleos’ (robust in Ancient Greek), re-ferring to the stout, compact nature of the teeth, and ‘Odous’(Ancient Greek), meaning tooth.

Type Species—Rhomaleodus budurovi, nov. sp.; neoselachianspecies known only from isolated teeth.

Included Species—The type species and “Hybodus” sp. (Sos-son and Martin, 1985:fig. 2b, b’).

Diagnosis—Tooth crown supported by a symmetrical toslightly asymmetrical, broad-based, triangular main cusp flankedby one or two pairs of smaller (less than 50% of main cusp height)lateral cusplets. All cusps and cusplets lingually inclined and or-namented with bifurcating, vertical ridges. A LSL runs parallel tothe crown-root interface. The root has a prominent lingual toruspenetrated by single row of large foramina; another row of foram-ina opens labially. Flat basal root face, except for a pronouncedlabial depression marked by large, circular foramina. Root vascu-larization of a primitive pseudo-polyaulacorhize type. A ratio of1.5:1 between the maximum baso-apical extent of the labial crowface and that of the labial root face. Noticeable heterodonty man-ifested by an increasing number of lateral cusplets (from one totwo pairs) and extent of the lingual torus from lateral towardsmore anterior files; posterior teeth low-crowned without devel-oped cusps. Microstructurally distinct enameloid tissue formedof a SLE covering a PBE layer lacking a radial component andconsisting of mutually subparallel bundles.

Distribution—The genus is recorded in the Anisian of Bulgariaand the Upper Triassic of the U.S.A.

Remarks—The presence of parallel-bundled enameloid iden-tifies Rhomaleodus, nov. gen., as a selachimorph neoselachian(following Reif, 1977, and Maisey et al., 2004). The ordinal affini-

FIGURE 3. Simplified line drawings of teeth of Rhomaleodus budurovi,nov. gen. et sp., representing the characteristic morphological features ofthe genus. A, the holotype (BU5240) in labial view; B, BU5243 in basalview with lingual face towards the top. Scale bars equal 200 µm.

ties of the genus, though, remain uncertain, considering that theoccurrence of SLE and a poorly structured PBE in the teeth ofRhomaleodus deviates from the better-organized triple-layeredenameloid of Synechodontiformes (Klug, 2010).

RHOMALEODUS BUDUROVI, nov. sp.(Figs. 3, 4, 6A–C)

Etymology of the Specific Name—Named after Dr. KirilBudurov, in recognition of his contribution to the biostratigraphyof the Triassic System.

Type Locality—Quarries Section (Stefanov, 1977; Muttoni,et al., 2000), 1 km north of the town of Belogradchik (VidinProvince, NW Bulgaria) along the Belogradchik-Gara Oreshetstertiary road.

Holotype—Completely preserved isolated tooth (BU5240;Figs. 3A, 4I–L), considered as belonging to the lateral dentition.

Paratypes—Five isolated teeth: BU5239 (Fig. 4E–H), BU5241(Fig. 4M–P), BU5242 (Fig. 4A–D), BU5243 (Figs. 3B, 4Q–S),BU5244 (Fig. 4T). The first four possess but display intact rootsbut displaying damage to the main cusp or lateral cusplets.BU5244 is a fragment of low-crowned posterior tooth.

BU5242 and BU5243 were treated with 3.4% HCl, which re-sulted in an extensive removal of the enameloid cover in BU5243;in contrast, BU5242 appears to be less affected structurally by theacid etching.

Occurrence—Babino Formation cropping out at the type local-ity (Fig. 1). Paragondolella bulgarica Conodont Zone (Budurovand Stefanov, 1975), Bithynian-Pelsonian Substages of theAnisian Stage (Middle Triassic).

Diagnosis—As for the genus.

Description

Morphology—Teeth of very small size, with the largest one(BU5241) having a crown mesio-distal length of 0.95 mm; thesmallest tooth of the type series is the holotype (BU5240),measuring 0.6 mm mesio-distally. BU5244 attains a mesio-distallength of 0.7 mm, but considering that this specimen is only par-tially preserved its real dimensions could be substantially greater.Maximum tooth height (baso-apical dimension) is attained at thelevel of the main cusp and reaches values of 0.4–0.5 mm. A ra-tio of ∼1.5:1 between labial crown and root height could be ac-curately determined only in the completely preserved BU5240tooth. Nevertheless, approximately the same dimensions can alsobe inferred with high degree of confidence for specimens BU5241and BU5243.

The crown bears a massive, triangular main cusp delimitedfrom a pair of flanking lateral cusplets by shallow notches on thelabial and lingual crown faces. The cusplets are in contact withthe main cusp and can attain 50% of its height. The mesial anddistal crown extremities of some specimens (BU5240, BU5241,

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FIGURE 4. Teeth of Rhomaleodus budurovi, nov. gen. et sp., from the Babino Formation, Anisian of Bulgaria. SEM micrographs. A–D, anterior?tooth BU5242 in labial (A), lingual (B), mesial (C), and occlusal (D) views; E–H, anterolateral? tooth BU5239 in labial (E), lingual (F), distal? (G),and occlusal (H) views. I–S, lateral? teeth; I–L, BU5240 in labial (I), lingual (J), mesial? (K), and occlusal (L) views; M–P, BU5241 in labial (M),lingual (N), mesial? (O), and occlusal (P) views; Q–S, BU5243 (surface-etched 5 seconds in 3.4% HCl) in labial (Q), lingual (R), and occlusal (S)views; T, fragmentary posterior? tooth (BU5244) in occlusal view. Scale bars equal 200 µm.

and BU5243) are slightly pointed and curved apically, closely re-sembling a pair of incipient cusplets apart from the lack of theircharacteristic ornamentation (Fig. 4I, M, Q). A second pair of lat-eral cusplets is positively identified, though, only in the crowns ofBU5239 and BU5242, with the mesial cusplet being the largerof the two (Fig. 4A, E). An uninterrupted occlusal crest runsmesio-distally through the apex of all cusp and cusplets. It is

offset lingually due to the curvature of the crown in that direc-tion. The labial crown face has flat to moderately concave pro-file and meets at an acute angle the labio-lingual plane of theroot. Labially, the crown ornamentation consists of prominentparallel to subparallel undulating, vertical ridges, which originatefrom the apices of all cusps. They tend to bifurcate halfway downthe crown face, whereas the areas between cusp and cusplets

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remain smooth. Basally, most of the ridges connect with the LSL,which runs close to the root-crow junction. The lingual crownface is moderately convex, contrasting with the flat to concaveat places (the regions of the inter-cusp hollows) labial surface(Fig. 4C, G, K, O). Wavy vertical ridges are descending from theapex of each cusp and are markedly shallower than their labialcounterparts. Most of these lingual ridges bifurcate basally nearthe LSL, yet not all of the resulting ramifications reach it. Thecrown extends beyond the mesial and distal margins of the root,but it also overhangs the entire neck portion of the tooth when inocclusal view.

The root has a bulky, compact appearance and provides strongsupport for the crown. It has an approximately trapezoidal out-line in basal view (Fig. 3B), with the lingual side being the short-est. A longitudinal furrow is developed circumferentially aroundthe root and divides it into an upper and a lower face. The con-stricted upper root face forms a conspicuous neck, which is de-void of foramina but marked by deep vertical striae. The lowerlabial root face exhibits a concave profile beneath the main cuspand is penetrated by a row of rounded foramina of varying size.The lingual extension of the lower root face forms a pronouncedtorus, pierced basally by a row of large, elliptical openings of un-equal diameter (60–87 µm). Additionally, the lingual root facebears a pair of smaller circular foramina situated at its distal?extremity (Fig. 4 G, K, R). They lie just beneath the longitudi-nal furrow and probably represent a continuation of the labialrow of foramina. The lingual section of the neck (upper rootface) is deeper (ratio of 1.4:1) than its labial half, resulting ina baso-apically shorter lingual crown face. The basal surface ofthe root is predominantly flat and featureless, except for a mesio-distally orientated depression close to the labial margin. In allspecimens it bears a minimum of two large (∼40 µm) foraminathat produce a series of indentations on the basal margin of thelabial root face; no grooves are associated with the openings inthis region.

BU5244 differs in certain aspects of its crown morphologywhen compared to the described above specimens. The tooth isdevoid of cusps; instead, the most prominent feature on the api-cal crown surface is the strong occlusal crest. Because of its pro-nounced lingual displacement, the ridges descending the labialcrown face are much longer than their lingual counterparts. Mostof the ridges originate independently from the occlusal crest, butsome diverge from a common apical starting point. All ridges de-scend the crown in a slightly undulating path and tend to bifurcate

just before merging with the LSL. The main root features complywith those diagnostic for the genus.

The examined specimens can be grouped into the three mor-photype categories, although determining the full range of toothmorphology variation of Rhomaleodus budurovi, nov. gen. etsp., is not possible at present due to paucity of the availablematerial:

Type A: Includes teeth (BU5239 and BU5242) with moderatelingual curvature of the main cusp, two pairs of lateral cusps,and weakly to well-developed lingual torus.

Type B: This morphology is encountered in BU5240, BU5241,and BU5243 and can be distinguished from the Type A spec-imens by the presence of only a single pair of lateral cuspsand extremely broad, strongly inclined main cusp.

Type C: Characteristic for BU5244.This tooth lacks developedcups; instead, the most elevated feature on the crown is thelingually displaced occlusal crest that traverses its length.The root has a pronounced labial projection but does notdisplay the medial thickening found in the remainder of thespecimens.

It is tentatively proposed that teeth of Type A occupied theanterior/anterolateral dental series, those of Type B formed partof the lateral tooth rows, whereas the one identified as Type Cbelonged to the posterior dentition.

Histology—The enameloid microstructure of Rhomaleodusbudurovi, nov. gen. et sp., is revealed by two surface-etched spec-imens (BU5242 [Fig. 6A, B] and BU5243 [Fig. 6C]). None of theteeth were sectioned because of their limited number; instead,the natural fractures occurring on the cusps of BU5243 were usedto discern the organization of the enameloid layer across its fullthickness.

At the level of the crown apex, the enameloid tissue is com-posed of two histologically distinct zones: an outer SLE and aninner PBE. Characteristic of the SLE are individual, randomlyoriented crystallites with rod-like appearance, varying in lengthbetween 0.9 and 1.2 µm. Their chaotic arrangement does notchange at the occlusal crest and the vertical ridges, where the SLEis more strongly developed (3–5.6 µm) in comparison to the thin(1.2–1.5 µm) covering between them. A PBE layer of an approx-imate 3 µm thickness, containing no traces of radial bundles, canbe observed beneath the SLE. This simple crystalline architec-ture could be a direct consequence of the limited depth of thePBE, leaving no adequate space for the formation of bundles

FIGURE 5. Tooth of Duffinselache holwellensis,nov. gen. (BRLSI M0067), from the Westbury For-mation, Rhaetian of England. SEM micrographs.A, lingual view; B, occlusal view; C, labial view; D,mesial view. Scale bars equal 1 mm in A–C and 200µm in D.

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FIGURE 6. A–C, microstructure of the enameloid layer in the teeth of Rhomaleodus budurovi, nov. gen. et sp. SEM micrographs. A, fracturedsurface at the apex of the first distal lateral cusplet of BU5242 showing the full thickness of the exposed enameloid layer and parts of the underlyingdentine. Tooth surface etched 5 seconds in 3.4% HCl. Scale bar equals 10 µm. B, detailed view of the upper right corner of image A, revealing theorganization of the superficial SLE (lower right) and the poorly structured crystalline bundles of the deeper PBE. Scale bar equals 2 µm. C, surfaceof the mesial? lateral cusplet of BU5243 after being surface etched 5 seconds in 3.4% HCl, demonstrating badly defined PBE bundles. Apical side tothe left. Scale bar equals 5 µm. D, SLE (bottom of the image) and PBE with well-developed parallel and radial bundles at the abraded apico-lingualsurface of the main cusp of Synechodus sp. (BU5245). Tooth surface-etched 5 seconds in 3.4% HCl. Scale bar equals 8 µm. SEM micrograph. E,F, enameloid microstructure of teeth of Duffinselache holwellensis, nov. gen. (BRLSI M0067). SEM micrographs. E, well-structured PBE devoid ofradial bundles at the surface of a tooth etched 40 seconds in 10% HCl. Scale bar equals 8 µm. F, transverse section along the mid region of a secondtooth, depicting the superficial parallel-bundled and the deeper tangled-bundled components of the enameloid layer, bordering the inner dentinaltissue. Tooth etched 5 seconds in 10% HCl. Scale bar equals 25 µm. Abbreviation: d, dentine.

perpendicular to the tooth’s long axis. All bundles are orientedin a general direction that is parallel to the outer crown surfaceand the long axis of the cusp. They attain a diameter of ∼1.5 µmand show density of approximately five bundles per every 10 µm.The bundles themselves consist of easily distinguishable, looselypacked crystallites, some of which may be slightly offset from themain course of each bundle. These crystallites have the same ul-trastructure as those described from the SLE.

In BU5243, the remaining patches of enameloid on one of theincipient lateral cusplets demonstrate grouping of single crystal-lites into ill-defined units of predominantly parallel orientationto the tooth surface, giving the tissue a loosely tangled appear-ance. These units are rarely organized into actual bundles andare not overlain by a SLE layer, which in all probability wasdissolved during the acid attack on the specimen. The loss ofstructure near the crown base commonly occurs in neoselachian

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enameloid (Cuny and Risnes, 2005), and apparently a unit rem-iniscent to the one described above was defined as primitivetangled-fibered enameloid in the Norian species Grozonodoncandaui (Cuny et al., 1998:fig. 4f).

The excessive removal of the enameloid covering fromBU5243 reveals the underlying orthodentine tissue, which en-closes an extensive pulp cavity. After etching, the orthodentinesurface is seen to be pitted by vast number of openings (diameter1.5–2 µm) that represent exposed dentinal tubules close to thejunction with the enameloid layer.

Comparison

Rhomaleodus, nov. gen., is defined on the basis of a uniquedental morphology combined with specific enameloid organiza-tion, which sets it apart from other neoselachian genera. Thissection serves the purpose of providing a differential analysis ofdental characters between Rhomaleodus, nov. gen., and other es-tablished or putative Triassic Selachimorpha.

Based on the presence of PBE microstructure, the tooth taxon?Palaeospinax sp. (Thies, 1982), reported from the Induan ofTurkey, is considered the stratigraphically oldest Triassic selachi-morph, whereas Synechodus antiquus (Early Permian of Russia)is recognized as the earliest known selachimorph, although itsenameloid histology is yet be studied (Ivanov, 2005). The Turk-ish material consists of a single incomplete tooth with faintly or-namented, acuminate main cusp, and at least one (probably apair) lateral cusplet. This contrasts strongly with the more blunt,triangular-shaped primary cusp of Rhomaleodus budurovi, nov.gen. et sp., and the prominent ridges of its crown ornament. How-ever, the enameloid tissue in both species is similarly organizedinto a superficial SLE of randomly orientated crystallites and aninner PBE without apparent radial bundles.

The rather squat, triangular-shaped cusps and bulky root, de-void of basally open grooves, allow differentiating the teeth ofRhomaleodus, nov. gen., from those of “Synechodus” sensu latoand Rhomphaiodon (Duffin, 1993; Johns et al., 1997; Cuny andBenton, 1999; Klug, 2010). Mucrovenator shares with Rhomale-odus, nov. gen., a lingually thickened root and a possible lackof TBE, but in contrast possesses radially parallel bundles andavascular labial root face (Cuny et al., 2001). The lack of typi-cal pseudo-polyaulacorhize root vascularization and descernableTBE casts doubt upon the inclusion of Mucrovenator withinSynechodontiformes according to the characters presently defin-ing the order (Klug, 2010). Hence, it is probably better to con-sider the genus a stem selachimorph.

Reifia minuta is another enigmatic neoselachian originally de-scribed by Duffin (1980) on the basis of several isolated teethfrom the Lower Norian of Germany. Since then, the genus hasbeen reported from the Anisian of Poland (Liszkowski, 1993),and later on Dorka (2001) demonstrated the Carnian age of thetype stratum (Dunkle Mergel), emending Duffin’s (1980) ini-tial stratigraphic placement of the taxon. Duffin (1980) assignedReifia to Galeomorphii (Superorder Galea sensu Shirai, 1996)on the basis of what he considered to be similarities in dentalmorphology with particular members of the orders Heterodon-tiformes, Orectolobiformes, and Carcharhiniformes, while disre-garding differences in enameloid microstructure and root vascu-larization (anaulacorhize), which infer more stemward positionof the taxon.

Reifia minuta can be separated from Rhomaleodus budurovi,nov. gen. et sp., by its smooth crown surface and the weakly de-veloped lateral cusps, which are not clearly differentiated fromthe main cusp by deep hollows. The root does not project lin-gually to the extent observed in Rhomaleodus, nov. gen., andlacks complete rows of labial and lingual foramina as well as basalroot depression.

Cuny et al. (1998) erected the genus Grozonodon, with a typespecies G. candaui, for isolated teeth dating from the Norianof France. Morphologically they are easily distinguished fromRhomaleodus, nov. gen., by their much greater dimensions (max-imum height of 6 mm) in combination with the incipient lat-eral cusps and denser vertical ridges that never attain the api-cal portion of the crown. Moreover, the root is missing a dis-tinct basal concavity, but instead it is depressed on its distal,mesial, and apico-lingual side. A portion of the root vascularcanals of Grozonodon candaui are seen on the lingual surface asrandomly arranged foramina, which depart from the even row ofopenings characteristic for the lower root face of Rhomaleodus,nov. gen.

Hueneichthys costatus is a Rhaetian neoselachian specieserected on the basis of a single badly abraded tooth (Reif, 1977).Compared to Rhomaleodus budurovi, nov. gen. et sp., it has morerobust crown, characterized by a massive principle cusp flankedby an asymmetrical pair of lateral cusps, which merge to a largedegree with the crown shoulders. A difference is also noticeablein the lack of distinguishable longitudinal shoulder line and inthe development of particularly strong ornament of thick verti-cal ridges. Unfortunately, the only available specimen of Huene-ichthys costatus does not have its root preserved, which poten-tially would have carried more meaningful systematic informa-tion. Despite the paucity of the material, Reif (1977) was ableto investigate the superficial microstructure of the enameloidlayer in Hueneichthys costatus and demonstrate well-developedradial bundles inside the PBE, found to be missing in the teeth ofRhomaleodus, nov. gen.

Pseudocetorhinus pickfordi is another Rhaetian neoselachianshark, introduced by Duffin (1998a) on the basis of isolated teethand frequently associated gill rakers. The species was placedwithin Cetorhinidae (Lamniformes) on the grounds of possess-ing similar to the Recent basking shark Cetorhinus maximus uni-cuspid, osteodont teeth with rudimentary cutting edges (Duffin,1998a). However, Cetorhinus is known for its strongly homod-ont dentition, characterized by stocky, irregularly shaped crownsand bulbous roots (Herman et al., 1993). It departs from the het-erodont dental pattern of Pseudocetorhinus, where lateral andposterior files develop pronounced heels (occasionally support-ing distal lateral cusps) and all teeth have lingually projectingroots (Duffin, 1998a). The known geological record of Cetorhi-nus extends back to the Eocene (Cappetta, 1987), whereas thatof Megachasma Taylor, Compagno, and Struhsaker, 1983, an-other filter-feeding lamniform, was recently pushed back (Shi-mada, 2007) to the Cenomanian (Late Cretaceous). Hence, a longghost lineage has to be assumed in order to establish phylogeneticrelationship between Pseudocetorhinus and the earliest membersof Cetorhinidae or Megachasmidae. It is more parsimonious toconclude that Pseudocetorhinus is in fact a stem selachimorph,which, despite similarities in its anterior tooth files to Recent fil-ter feeding lamniforms, differs strongly from their specialized ho-modont dentition. It differs from Rhomaleodus budurovi, nov.gen. et sp., by the possession of a single cusp in all tooth posi-tions, lack of strong crown ornament, labially low roots devoidof a basal depression, and root faces penetrated by multitude offoramina not organized into rows.

Genus DUFFINSELACHE, nov. gen.(Figs. 5, 6E, F)

Derivation of Name—In honor of Christopher J. Duffin whofirst recognized this species, appreciating his tremendous workon basal neoselachians over the years, and ‘Selachos,’ meaningshark in Ancient Greek.

Type Species—Duffinselache holwellensis (Duffin, 1998b).Emended Diagnosis (modified from Duffin, 1998b)— Slim,

elongate teeth (Fig. 5) measuring up to 4.1 mm mesio-distallyand showing mild linear gradient monognathic heterodonty. The

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central cusp is low. There are no lateral cusplets. Non-branchingvertical ridges ascend the crown from the crown shoulder bothlabially and lingually. The enameloid is triple-layered with PBElacking radial bundles (Fig. 6E, F) and a much reduced TBE.The root is sub-equal to the crown in depth and firmly attachedto the latter.

Distribution—This genus is currently restricted to theRhaetian of England, France, and Belgium.

Remarks—“Polyacrodus” holwellensis was erected by Duffin(1998b) as a hybodont genus, although most of the teeth werefound with their root still attached to the crown, a rare fea-ture among hybodonts, but quite characteristic of neoselachiansharks. Indeed, a microstructure study made by one of us (G.C.)has revealed the presence of a SCE, PBE, and what appears to bea much reduced TBE. Therefore, a new genus needs to be erectedfor this neoselachian species, and we propose here to name itDuffinselache holwellensis, nov. gen.

The ordinal affinities of Duffinselache holwellensis are cur-rently unclear. Because it does not possess radial bundles, lin-gual torus and vascular grooves entering a concavity on the labio-basal root face, the species is not considered a member of Syne-chodontiformes. Duffinselache, nov. gen., is easily separated fromRhomaleodus, nov. gen., by having elongated teeth with a lowmain cusp and lingually restricted roots penetrated by unevenlydistributed foramina. On the other hand, its general morphol-ogy is quite similar to that of Pseudocetorhinus pickfordi lateralteeth, but certain key morphohistological differences suggest thatthe two taxa are not congeneric. These concern the absence fromDuffinselache, nov. gen., of radial enameloid bundles, distal lat-eral cusplet, and multiple vascular openings on the basal rootface, all of which are features of P. pickfordi teeth.

DISCUSSION

Pre-Jurassic Evolution of Neoselachian Sharks

The Neoselachii are considered to be the sister group of hy-bodonts (Maisey et al., 2004), and because the latter first ap-peared in the Devonian (Hairapetian and Ginter, 2009), it canbe inferred that neoselachians also evolved during this Period.At present, the late Emsian—Early Eifelian species Mcmurdo-dus whitei (Turner and Young, 1987) and the Givetian Mcmur-dodus featherensis (White, 1968) are included by some authors(Burrow et al., 2008; Ginter et al., 2010) within Neoselachii. Theclaim made by Burrow et al. (2008) that Mcmurdodus is closelyrelated to either Echinorhiniformes or Hexanchiformes is at bestdoubtful, because it relies mainly on features prone to homo-plasy such as crown morphology, or the osteodentine composi-tion of the root and crown base passing into orthodentine insidethe cusps, which occurs also in Xenacanthiformes (Hampe, 2003)among early elasmobranchs.

The uncertainty surrounding the systematic position of Mc-murdodus exemplifies well the general lack of useful charactersallowing the identification of basal neoselachians. Indeed, norecord of bundled enameloid (diagnostic for Neoselachii exclu-sive of batomorphs, i.e., Selachimorpha; Reif, 1977; Maisey et al.,2004) has been demonstrated for potential stem-neoselachiangenera in the Paleozoic (see Ginter et al., 2010, for a review);the structures illustrated by Burrow et al. (2008:fig. 1O) are quitedifficult to interpret. This probably implies that the enameloid inthe teeth of stem-neoselachians was devoid of crystalline bundles,conforming with the entirely SCE of basal Batomorphii (Cunyet al., 2009), which are recognized as sister group of Selachimor-pha (Douady et al., 2003; Maisey et al., 2004; Winchell et al.,2004). Of particular interest in this connection are the affini-ties of the Paleozoic family Anachronistidae (Duffin and Ward,1983), known from several Mississippian to Guadalupian toothspecies referred to the genus Cooleyella (Gunnell, 1933; Duffinand Ward, 1983; Duffin et al., 1996; Ivanov et al., 2007) and the

monospecific Ginteria, reported from the Visean-Serpukhovianinterval of Russia and Britain (Duffin and Ivanov, 2008; Ginteret al., 2010). Using root morphology as a conservative trait ofpotential systematic significance at or above ordinal level, thesetaxa can confidently be included within Neoselachii, taking intoaccount their hemiaulacorhize root vascularization. This was ac-knowledged by Duffin and Ward (1983), who placed Cooleyellaclose to crown-neoselachians on grounds of similarly developed(as in the genera Squatina and Orectolobus) labial buttress andmedian concavity of the root base. The histological investiga-tion of Cooleyella fordi teeth, performed by one of us (G.C.,pers. observ.), established haphazardly arranged single crystal-lites organized into larger structures perpendicular to the outersurface of the enameloid layer, suggesting a more stemward po-sition for Anachronistidae (contra Duffin and Ward, 1983). Atthe current state of our knowledge, Cooleyella and Ginteria areto be regarded as stem-neoselachians or possibly stem-groupbatomorphs. A tentative support for the latter statement canbe sought in the sporadic presence of partially enclosed nutri-ent groove (leading to hemiaulacorhizy) in some of the earliestunequivocal rhinobatiforms, namely the Middle Jurassic speciesBelemnobatis kermacki (Underwood and Ward, 2004:pl. 13, fig.10; pl. 14, figs. 2, 5), B. stahli (Underwood and Ward, 2004:pl.14, fig. 8), and B. aominensis (Cuny et al., 2009), and the UpperJurassic Spathobatis bugesiacus (Underwood, 2002:text-fig. 5i).The enameloid layer of B. aominensis teeth was demonstratedby Cuny et al. (2009) to consist of individual, randomly orientedcrystallites, reaffirming the plesiomorphic state of SCE withinBatomorphii.

In the Triassic there are still a number of presumptive stem-neoselachian or stem-batomorph tooth genera devoid of bun-dled enameloid (Doratodus, Vallisia, Pseudodalatias; Rees andCuny, 2007; Cuny et al., 2009). A close relationship between Val-lisia coppi (Duffin, 1982) and Doratodus tricuspidatus (Schmid,1861; Seilacher, 1943; Duffin, 1981) must be assumed, when weconsider that both share a characteristic strongly pronouncedflange developed at the crown base, marked constriction of theroot near the crown junction, and predominantly poorly struc-tured SCE (Duffin, 1981; Cuny and Benton, 1999). Unfortu-nately, no specimens of Doratodus teeth with completely in-tact roots have been recovered so far, thus preventing a di-rect comparison with the holaulacorhize vascularization (Duf-fin, 1982) of Vallisia. Pseudodalatias (known from the speciesP. henarejensis [Ladinian; Botella et al., 2009b] and P. barn-stonensis [Norian–Rhaetian; Sykes, 1971; Cuny, 1998]), in con-trast to the above-mentioned genera, displays highly specializedcutting-clutching dentition with strong serrations on the crownsof the lower? tooth files. The root is bilobed with a narrow me-dial groove (Botella et al., 2009b), but lacking the major basalforamen of Vallisia (Duffin, 1982). More interestingly, the indi-vidual crystallites of Pseudodalatias enameloid layer are denselypacked and oriented perpendicular to the tooth surface in the in-ner part of the tissue, whereas superficially they change orienta-tion and run parallel to it (Cuny and Benton, 1999; Botella et al.,2009b). This highly structured SCE has probably purely adaptivesignificance, because similar compaction of crystallites has beendemonstrated (Duffin and Cuny, 2008) in some hybodonts (Pri-ohybodus d’Erasmo, 1960, Thaiodus Cappetta et al., 1990) andCarcharopsis prototypus Agassiz, 1843 (Elasmobranchii incertaesedis following Ginter et al., 2010), which possess serrated crownmargins. The derived enameloid histology of Pseudodalatias is instark contrast with the plesiomorphic state for Chondrichthyes(Gillis and Donoghue, 2007; Botella et al., 2009a) that is madeof randomly arranged crystallites and present in Doratodus andVallisia (additionally, the latter possesses an outer zone of crys-tallites aligned orthogonal to the crown surface; Cuny and Ben-ton, 1999). Given the inadequate data on the polarity of dentalcharacters among stem-neoselachians, it is difficult at present to

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resolve the systematic position of Pseudodalatias relative to theDoratodus-Vallisia group.

The first known record of selachimorph neoselachians datesfrom the Early Permian (Ivanov, 2005). However, a triple-layeredenameloid organization, including well-defined SLE, PBE, andTBE, has not been demonstrated before the Late Carnian (Syne-chodus multinodosus; Johns et al., 1997) and seems to be mainlyrestricted to certain Synechodontiformes (Synechodus multino-dosus and Rhomphaiodon) as well as some rare, more primi-tive Selachimorpha (Grozonodon and Pseudocetorhinus). Duffin(1980) claimed to have identified triple-layered enameloid struc-ture in the Early Norian teeth of Reifia minuta. The tissue isshown to possess superficial SLE composed of large crystals withminimum length of 2 µm on top of a PBE zone devoid of ra-dial bundles. The presence of the TBE, however, is questionable,especially when we consider that the micrographs provided asevidence of its existence (Duffin, 1980:fig. 3e, f) probably depictthe structureless enameloid commonly detected in neoselachianteeth close to the enameloid-dentine boundary.

The presence of a triple-layered enameloid cannot be satisfac-torily demonstrated or remains doubtful in “Synechodus” incre-mentum and “S.” rhaeticus (Johns et al., 1997; Cuny and Risnes,2005) so that their attribution to the genus Synechodus, and evento the order Synechodontiformes, is questionable. The enameloidultrastructure of “S.” incrementum was misinterpreted by Johnset al. (1997), who concluded that the depicted (pl. 7, figs. 1–3) mu-tually parallel rod-like structures represent crystalline bundles,when in fact they are of diagenetic origin. Judging from the re-mainder of the available SEM images (Johns et al., 1997:pl. 7,figs. 4–9), the enameloid layer of “S.” incrementum appears tobe made of outer compacted single crystallites aligned perpen-dicular to the tooth surface and inner single crystalline bundlesof woven texture, departing from the typical neoselachian con-dition and approaching more the hybodont enameloid histology(Cuny et al., 2001).

A number of Selachimorpha appear to possess enameloiddominated by SCE and poorly structured PBE (“Palaeospinax”sp. [Thies, 1982], Rhomaleodus, nov. gen., “Synechodus” volati-cus, Reifia). As these taxa are within the size range (1–1.5 mm)of species (Synechodus multinodosus, Rhomphaiodon minor)with typical triple-layer enameloid, there does not seem to bea constraint on the complexity of enameloid architecture im-posed by the tooth size. This suggests a step-by-step acquisi-tion of the triple-layered enameloid organization, beginning withthe appearance of PBE, followed by that of TBE; the SLE be-ing probably a remnant of the primitive SCE. However, the de-velopment of the PBE seems also to be gradual, with a primi-tive state devoid of radial bundles (“Palaeospinax” sp. [Thies,1982], Rhomaleodus, nov. gen., Reifia, Duffinselache nov. gen.,and “Synechodus” rhaeticus). Further compounding the evolu-tionary history of neoselachian enameloid is the indication ofapparent phases in the emergence of the bundles themselves.Ultrastructurally, the bundles of the Early and Middle Trias-sic forms “Palaeospinax” sp. (Thies, 1982), Rhomaleodus, nov.gen., and Reifia are poorly organized, with their constituent crys-talline fibers loosely packed, displaying easily discernable sin-gle crystallites. The bundle histology described above is likely tobe a plesiomorphic character for Selachimorpha, implying thatthese three genera have retained a basal enameloid architecture,despite discrepancies in their dental morphology. The derivedstate of PBE appears to have emerged during the Middle–LateTriassic (encountered in Hueneichthys, Pseudocetorhinus, Gro-zonodon, Rhomphaiodon, Synechodus), being characterized byhighly structured parallel and radial bundles.

Finally, there is an indication that evolution of the tangledcomponent of the enameloid layer proceeded in a non-linearmanner, as it is reported to be missing from Mucrovenator (Cunyet al., 2001), which otherwise possess a well-developed PBE.

CONCLUSIONS

The identification of the basal selachimorphs Rhomaleodusbudurovi, nov. gen. et sp. (Anisian of Bulgaria), and Duffin-selache, nov. gen. (Rhaetian of Western Europe), combined withthat of the synechodontiform Synechodus sp. (Anisian of Bul-garia), adds to our knowledge on the early stages of neoselachianevolution. The presented data demonstrate the applicability ofenameloid histology as systematic tool for resolving relationshipsamong stem Neoselachii. Moreover, examination of the enam-eloid ultrastructure in the new taxa helps trace out the followingconsecutive steps, which led to acquisition of a triple-layered or-ganization in this hypermineralized tissue during the Triassic:

1. Development of subparallel to parallel crystalline bundles,probably by modification of the SCE retained only as a thinsuperficial SLE layer.

In Recent selachimorphs, at the onset of enameloid crystal-logenesis, the portion of the organic matrix closest to the innerdental epithelium displays randomly oriented single crystals(corresponding to the SLE) separated by a poorly mineral-ized zone from the inner, tightly packed, and mutually alignedcrystals forming the PBE (Kemp, 1985; Sasagawa, 1998, 1999);in batomorphs, the enameloid mineralizes by nucleation ofchaotically oriented crystallites throughout the entire thick-ness of the tissue (Sasagawa, 2002). It is difficult to ascer-tain from developmental studies alone whether or not PBEarose de novo in Selachimorpha, but the fossil evidence pointsmore strongly towards a gradual differentiation and increasein structural complexity of the ancestral SCE through severalphases.

1.1. Formation of loosely packed subparallel bundles com-posed of single crystallites (evolved in the Palaeozoic).

1.2. Transformation of individual bundle crystallites intoelongated crystalline fibers accompanied by compactionand increase in the order of bundle organization.

1.3. Development of radial bundles as component of the PBE.

2. Acquisition of TBE at the junction with the adjacent dentinetissue, most likely by alteration of the already existing bundledarchitecture of the PBE.

The tangled enameloid appears to have had patchy distri-bution among Triassic selachimorphs. This could reflect eitherits secondary loss in certain species or alternatively it might becaused by retention of the plesiomorphic state for the clade,i.e., an enameloid made only of SLE and PBE. It must benoted in this connection that the parallel and tangled enam-eloid seem to be developmentally decoupled, as evidenced inthe posterior teeth of the crown neoselachian Heterodontus(exhibiting only SLE and TBE; Reif, 1977), indicating that aloss of one of these structural units does not necessarily affectthe other.

ACKNOWLEDGMENTS

The authors wish to thank Dr. Lyudmila Petrunova (Geologi-cal Institute, Bulgarian Academy of Sciences) for kindly donatingthe Anisian neoselachian teeth studied in the present work. Theinitial phase of this scientific investigation was conducted dur-ing the “Elasmobrach teeth enameloid microstructure as a tax-onomic criterion” training course funded by the European Dis-tributed Institute of Taxonomy.

LITERATURE CITED

Agassiz, L. 1837–1843. Recherches sur les poissons fossiles. Tome 3 con-tenant l’histoire de l’ordre des placoides. Imprimerie de Petitpierre,Neufchatel, 390 pp.

Dow

nloa

ded

by [

Uni

vers

ity o

f Sa

skat

chew

an L

ibra

ry]

at 1

3:36

04

Oct

ober

201

2

ANDREEV AND CUNY—ENAMELOID OF TRIASSIC NEOSELACHIANS 265

Angelov, V., M. Antonov, S. Gerdzhikov, I. Klimov, P. Petrov, H. Kiseli-nov, and G. Dobrev. 2006. Geological map of Bulgaria 1:50 000, mapsheet K-34-21-B (Knyazhevats) and K-34-22-A (Belogradchik), V.Angelov and Kh. Khrischev (eds.). Ministry of Environment andWater, Bulgarian National Geological Survey, Sofia.

Bonaparte, C. L. 1838. Synopsis Vertebratorum Systematis. Nuovi Annalidelle Scienze Naturali (Bologna), series 1 2:105–133.

Botella, H., P. C. J. Donoghue, and C. Martinez-Perez. 2009a. Enameloidmicrostructure in the oldest known chondrichthyan teeth. Acta Zo-ologica 90:103–108.

Botella, H., P. Plasencia, A. Marquez-Aliaga, G. Cuny, and M. Dorka.2009b. Pseudodalatias henarejensis nov. sp. A new pseudodalatiid(Elasmobranchii) from the Middle Triassic of Spain. Journal of Ver-tebrate Paleontology 29:1006–1012.

Budurov, K. Y. 1977. Revision of the late Triassic platform conodonts.Geologica Balcanica 7:31–48.

Budurov, K. Y. 1980. Conodont stratigraphy of the Balkanide Triassic.Rivista Italiana di Paleontologia e Stratigrafia 85:767–780.

Budurov, K. Y., and S. A. Stefanov. 1972. Plattform-Conodonten ausder Mittleren Trias Bulgariens. Mitteilungen der Gesellschaft derGeologie- und Bergbaustudenten 21:829–852.

Budurov, K. Y., and S. A. Stefanov. 1973. Etliche neue Plattform-Conodonten aus der Mitteltrias Bulgariens. Dokladi na BulgarskataAkademia na Naukite 26:803–806.

Budurov, K. Y., and S. A. Stefanov. 1974. Die Zahnreihen-Conodontenaus der Trias des Golo-Bardo Gebirges. Bulletin of the Geologi-cal Institute (Bulgarian Academy of Sciences), series Paleontology23:89–104.

Budurov, K. Y., and S. A. Stefanov. 1975. Neue daten uber die Conodon-tenchronologie der Balkaniden mittleren Trias. Dokladi na Bulgar-skata Akademia na Naukite 28:791–794.

Burrow, C. J., D. C. Hovestadt, M. Hovestadt-Euler, S. Turner, and G.C. Young. 2008. New information on the Devonian shark Mcmur-dodus, based on material from western Queensland, Australia. ActaGeologica Polonica 58:155–163.

Cappetta, H. 1987. Chondrichthyes II: Mesozoic and Cenozoic Elasmo-branchii. Gustav Fisher Verlag, Stuttgart, New York, 193 pp.

Cappetta, H., E. Buffetaut, and V. Suteethorn. 1990. A new hybodontshark from the Lower Cretaceous of Thailand. Neues Jahrbuch furGeologie und Palaontologie, Monatshefte 1990 (11):659–666.

Chatalov, A., and G. Doneva. 2009. Sedimentological characteristicsof Iskar Carbonate Group (Middle Triassic) in the Belogradchikregion—preliminary results; pp. 65–66 in R. Nakov (ed.), Bulgar-ian Geological Society Geosciences 2009—Proceedings, Sofia, 3–4December. Bulgarian Geological Society, Sofia.

Compagno, L. J. V. 1977. Phyletic relationships of living sharks and rays.American Zoologist 17:303–322.

Cuny, G. 1998. Primitive neoselachian sharks: a survey. Oryctos 1:3–21.Cuny, G., and M. J. Benton. 1999. Early radiation of the neoselachian

sharks in Western Europe. Geobios 32:193–204.Cuny, G., M. Martin, R. Rauscher, and J. M. Mazin. 1998. A new

neoselachian shark from the upper Triassic of Grozon (Jura,France). Geological Magazine 135:657–668.

Cuny, G., O. Rieppel, and P. M. Sander. 2001. The shark fauna fromthe Middle Triassic (Anisian) of North-Western Nevada. Zoologi-cal Journal of the Linnean Society 133:285–301.

Cuny, G., and S. Risnes. 2005. The enameloid microstructure of theteeth of synechodontiform sharks (Chondrichthyes: Neoselachii).Palarch’s Journal of Vertebrate Palaeontology 3:8–19.

Cuny, G., P. Srisuk, S. Khamha, V. Suteethorn, and H. Tong. 2009. A newelasmobranch fauna from the Middle Jurassic of southern Thailand;pp. 97–113 in E. Buffetaut, G. Cuny, J. Le Loeuff, and V. Suteethorn(eds.), Late Palaeozoic and Mesozoic Ecosystems in SE Asia. TheGeological Society, London, Special Publications, London.

de Carvahlo, M. R. 1996. Higher-level elasmobranch phylogeny, basalsqualeans, and paraphyly; pp. 35–62 in M. L. J. Stiassny, L. R. Par-enti, and G. D. Johnson (eds.), Interrelationships of Fishes. Aca-demic Press, San Diego.

d’Erasmo, G. 1960. Nuovi avanci ittiolitici della “serie di Lugh” in So-malia conservati nel Museo Geologico di Firenze. PalaeontographiaItalica 55:1–23.

Dorka, M. 2001. Shark remains from the Triassic of Schoningen, LowerSaxony, Germany. Neues Jahrbuch fur Geologie und Palaontologie,Abhandlungen 221:219–247.

Douady, C. J., M. Dosay, M. S. Shivji, and M. J. Stanhope. 2003. Molecu-lar phylogenetic evidence refuting the hypothesis of Batoidea (rays

and skates) as derived sharks. Molecular Phylogenetics and Evolu-tion 26:215–221.

Duffin, C. J. 1980. A new euselachian shark from the Upper Triassic ofGermany. Neues Jahrbuch fur Geologie und Palaontologie, Monat-shefte 1:1–16.

Duffin, C. J. 1981. Comments on the selachian genus Doratodus Schmid(1861) (Upper Triassic, Germany). Neues Jahrbuch fur Geologieund Palaontologie, Monatshefte 5:289–302.

Duffin, C. J. 1982. A palaeospinacid shark from the Upper Triassicof south-west England. Zoological Journal of the Linnean Society74:1–7.

Duffin, C. J. 1993. Late Triassic shark’s teeth (Chondrichthyes, Elasmo-branchii) from Saint-Nicolas-de-Port (north-east France); pp. 7–32in J. Herman and H. Van Waes (eds.), Professional Paper of theBelgian Geological Survey, 264: Elasmobranches et Stratigraphie.Belgian Geological Survey, Brussels.

Duffin, C. J. 1998a. New shark remains from the British Rhaetian (latestTriassic) 1. The earliest basking shark. Neues Jahrbuch fur Geologieund Palaontologie, Monatshefte 3:157–181.

Duffin, C. J. 1998b. New shark remains from the British Rhaetian (lat-est Triassic) 2. Hybodonts and palaeospinacids. Neues Jahrbuch furGeologie und Palaontologie, Monatshefte 4:240–256.

Duffin, C. J., and G. Cuny. 2008. Carcharopsis prototypus and the adapta-tions of single crystallite enameloid in cutting dentitions. Acta Geo-logica Polonica 58:181–184.

Duffin, C. J., and A. Ivanov. 2008. New chondrichthyan teeth from theEarly Carboniferous of Britain and Russia. Acta Geologica Polonica58:191–197.

Duffin, C. J., and D. J. Ward. 1983. Neoselachian shark’s teeth from theLower Carboniferous of Britain and the Lower Permian of the USA.Palaeontology 26:93–110.

Duffin, C. J., and D. J. Ward. 1993. The Early Jurassic palaeospinacidsharks of Lyme Regis, southern England; pp. 53–102 in J. Hermanand H. Van Waes (eds.), Professional Paper of the Belgian Geolog-ical Survey, 264: Elasmobranches et Stratigraphie. Belgian Geologi-cal Survey, Brussels.

Duffin, C. J., M. Richter, and P. A. Neis. 1996. Shark remains from theLate Carboniferous of the Amazon Basin, Brazil. Neues Jahrbuchfur Geologie und Palaontologie, Monatshefte 4:232–256.

Gillis, J. A., and P. C. J. Donoghue. 2007. The homology and phylogeny ofchondrichthyan tooth enameloid. Journal of Morphology 268:33–49.

Ginter, M., O. Hampe, and C. J. Duffin. 2010. Chondrichthyes, PaleozoicElasmobranchii: Teeth. Verlag Dr. Friedrich Pfeil, Munich, 168 pp.

Guinot, G., and H. Cappetta. 2011. Enameloid microstructure ofsome Cretaceous Hexanchiformes and Synechodontiformes (Chon-drichthyes, Neoselachii): new structures and systematic implica-tions. Microscopy Research and Technique 74:196–205.

Gunnell, F. H. 1933. Conodonts and fish remains from the Chero-kee, Kansas City, and Wabaunsee. Journal of Paleontology 7:261–297.

Hairapetian, V., and M. Ginter. 2009. Famennian chondrichthyan re-mains from the Chahriseh section, central Iran. Acta GeologicaPolonica 59:173–200.

Hampe, O. 2003. Revision of the Xenacanthida (Chondrichthyes:Elasmobranchii) from the Carboniferous of the British Isles.Transactions of the Royal Society of Edinburgh—Earth Sciences93:191–237.

Hay, O. P. 1902. Bibliography and catalogue of the fossil Vertebrata ofNorth America. Bulletin of the United States Geological Survey179:1–868.

Herman, J., M. Hovestadt-Euler, and D. C. Hovestadt. 1993. Contri-butions to the study of the comparative morphology of teeth andother relevant ichthyodorulites in living supraspecifc taxa of chon-drichthyan fishes. Part A: Selachii. Bulletin de l’Institut Royal desSciences Naturelles de Belgique, Biologie 63:185–256.

Huxley, T. H. 1880. On the application of the laws of evolution to thearrangement of the Vertebrata and more particular the Mammalia.Proceedings of the Zoological Society of London 1880:649–662.

Ivanov, A., M. Nestell, and G. Nestell 2007. Middle Permian chon-drichthyans from west Texas and relationships of the Jalodontidae.;pp. 48 in H. Blom, and M. D. Brazeau (eds.), 40th Anniversary Sym-posium on Early Vertebrates/Lower Vertebrates. Ichthyolith Issues,Special Publication 10. Uppsala University, Sweden.

Ivanov, A., and T. Klets. 2007. Triassic marine fishes from Siberia, Russia;pp. 108–109 in S. G. Lucas and J. A. Spielmann (eds.), The GlobalTriassic. New Mexico Museum of Natural History and Science

Dow

nloa

ded

by [

Uni

vers

ity o

f Sa

skat

chew

an L

ibra

ry]

at 1

3:36

04

Oct

ober

201

2

266 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 32, NO. 2, 2012

Bulletin 41. New Mexico Museum of Natural History and Science,Albuquerque.

Ivanov, A., M. Nestell, and G. Nestell. 2007. Middle Permian chon-drichthyans from west Texas and relationships of the Jalodontidae.;pp. 48 in H. Blom, and M. D. Brazeau (eds.), 40th Anniversary Sym-posium on Early Vertebrates/Lower Vertebrates. Ichthyolith Issues,Special Publication 10. Uppsala University, Sweden.

Johns, M. J., C. R. Barnes, and M. J. Orchard. 1997. Taxonomy and bios-tratigraphy of Middle and Late Triassic elasmobranch ichthyolithsfrom northeastern British Columbia. Geological Survey of CanadaBulletin 502. Geological Survey of Canada, Ottawa, 235 pp.

Kemp, N. E. 1985. Ameloblastic secretion and calcification of the enamellayer in shark teeth. Journal of Morphology 184:215–230.

Klug, S. 2009. A new palaeospinacid shark (Chondrichthyes, Neoselachii)from the Upper Jurassic of Southern Germany. Journal of Verte-brate Paleontology 29:326–336.

Klug, S. 2010. Monophyly, phylogeny and systematic position of the dag-ger Synechodontiformes (Chondrichthyes, Neoselachii). ZoologicaScripta 39:37–49.

Kriwet, J., and S. Klug. 2004. Late Jurassic selachians (Chondrichthyes,Elasmobranchii) from southern Germany: re-evaluation on taxon-omy and diversity. Zitteliana A 44:67–95.

Leidner, A., and D. Thies. 1999. Placoid scales and oral teeth of LateJurassic elasmobranchs from Europe; pp. 29–40 in G. Arratia andH.-P. Schultze (eds.), Mesozoic Fishes 2—Systematics and FossilRecord. Verlag Dr. Friedrich Pfeil, Munich.

Liszkowski, J. 1993. Die Selachierfauna des Muschelkalks in Polen:Zusammensetzung, Stratigraphie und Palaookologie; pp. 177–185in H. Hagdorn and A. Seilacher (eds.), Muschelkalk. SchontalerSymposium 1991. (Sonderbande der Gesellschaft fur Naturkunde inWurttemberg, Bd. 2) Goldschneck-Verlag, Stuttgart.

Mackie, S. J. 1863. On a new species of Hybodus from the Lower Chalk.The Geologist 6:241–246.

Maisey, J. G. 1984. Chondrichthyan phylogeny: a look at the evidence.Journal of Vertebrate Paleontology 4:359–371.

Maisey, J. G. 1985. Cranial morphology of the fossil elasmobranch Syne-chodus dubrisiensis. American Museum Novitates 2804:1–28.

Maisey, J. G., G. J. P. Naylor, and D. J. Ward. 2004. Mesozoic elas-mobranchs, neoselachian phylogeny and the rise of modern elas-mobranch diversity; pp. 17–56 in G. Arratia and A. Tintori (eds.),Mesozoic Fishes 3—Systematics, Paleoenvironments and Biodiver-sity. Verlag Dr. Friedrich Pfeil, Munich.

Muttoni, G., M. Gaetani, K. Budurov, I. Zagorchev, E. Trifonova,D. Ivanova, L. Petrounova, and W. Lowrie. 2000. Middle Tri-assic paleomagnetic data from northern Bulgaria: constraints onTethyan magnetostratigraphy and paleogeography. Palaeogeogra-phy, Palaeoclimatology, Palaeoecology 160:223–237.

Naylor, G. J. P., J. A. Ryburn, O. Fedrigo, and A. Lopez. 2005. Phy-logenetic relationships among the major lineages of modern elas-mobranchs; pp. 1–25 in W. C. Hamlett (ed.), Reproductive Biologyand Phylogeny of Chondrichthyes. Science Publishers, Enfield, NewHampshire.

Nelson, J. S. 1984. Fishes of the World. John Wiley and Sons, New York,523 pp.

Rees, J., and G. Cuny. 2007. On the enigmatic neoselachian Agaleusdorsetensis from the European Early Jurassic. GFF (GeologiskaForeningens i Stockholm Forhandlingar) 129:1–6.

Regan, C. T. 1906. A classification of selachian fishes. Proceedings of theZoological Society of London 1906:722–758.

Reif, W.-E. 1977. Tooth enameloid as a taxonomic criterion: 1. A new eu-selachian shark from the Rhaetic-Liassic boundary. Neues Jahrbuchfur Geologie und Palaontologie, Monatshefte 9:565–576.

Sasagawa, I. 1998. Mechanisms of mineralization in the enameloid of elas-mobranchs and teleosts. Connective Tissue Research 39:207–214.

Sasagawa, I. 1999. Fine structure of dental epithelial cells and theenameloid during the enameloid formation stages in an elasmo-branch, Heterodontus japonicus. Anatomy and Embryology 200:477–486.

Sasagawa, I. 2002. Mineralization patterns in elasmobranch fish. Mi-croscopy Research and Technique 59:396–407.

Schmid, E. E. 1861. Die Fischzahne der Trias bei Jena. Nova ActaAcademia Leopoldiana-Carolinensis 21:1–42.

Seilacher, A. 1943. Elasmobranchier-Reste aus dem oberen Muschelkalkund dem Keuper Wurttembergs. Neues Jahrbuch fur Mineralogie,Geologie und Palaontologie, Monatshefte B 10:273–292.

Shimada, K., 2007. Mesozoic origin for megamouth shark (Lamniformes:Megachasmidae). Journal of Vertebrate Paleontology 27:512–516.

Shirai, S. 1992. Squalean Phylogeny: A New Framework of “Squaloid”Shark and Related Taxa. Hokkaido University Press, Sapporo, 151pp.

Shirai, S. 1996. Phylogenetic Interrelationships of Neoselachians (Chon-drichthyes: Euselachii); pp. 9–34 in M. L. J. Stiassny, L. R. Parenti,and G. D. Johnson (eds.), Interrelationships of Fishes. AcademicPress, San Diego.

Sosson, M., and M. Martin. 1985. Decouverte d’une faune de Ver-tebres marins du Trias superieur dans Ie Hot Springs Range(nord-ouest du Nevada, U.S.A.): implications paleogeographiques.Comptes Rendus de l’Academie des Sciences, Serie II 5:177–180.

Stefanov, S. A. 1977. Biostratigraphy of the Balkanide Carbonate Trias-sic on the basis of conodonts and fish remains. Geologica Balcanica7:65–84.

Sudar, M. N., and K. J. Budurov. 1979. New conodonts from the Triassicin Yugoslavia and Bulgaria. Geologica Balcanica 9:47–52.

Sykes, J. H. 1971. A new dalatiid fish from the Rhaetic Bond Bed at Barn-stone, Nottinghamshire. Mercian Geologist 4:13–22.

Taylor, L. R., L. J. V. Compagno, and P. J. Struhsaker. 1983.Megamouth—a new species, genus, and family of lamnoid shark(Megachasma pelagios, Family Megachasmidae) from the Hawai-ian Islands. Proceedings of the California Academy of Science43:87–110.

Thies, D. 1982. A neoselachian shark tooth from the Lower Trias-sic of the Kocaeli (= Bithynian) Peninsula, W. Turkey. NeuesJahrbuch fur Geologie und Palaontologie, Monatshefte 5:272–278.

Thies, D. 1983. Jurazeitliche Neoselachier aus Deutschland und S-England. Courier Forschungsinstitut Senckenberg 58:117.

Thies, D., and W.-E. Reif. 1985. Phylogeny and evolutionary ecology ofMesozoic Neoselachii. Neues Jahrbuch fur Geologie und Palaon-tologie, Abhandlungen 169:333–361.

Tronkov, D. 1973. Fundamentals of the Triassic stratigraphy in the Be-logradchik anticlinorium (Northwestern Bulgaria). Proceedings ofthe Geological Institute, ser. Stratigraphy and Lithology 22:73–98.[Bulgarian]

Tronkov, D. 1981. Stratigraphy of the Triassic System in part of thewestern Srednogorie (West Bulgaria). Geologica Balcanica 11:3–20.[Russian]

Turner, S., and G. C. Young. 1987. Shark Teeth from the Early-Middle Devonian Cravens Peak Beds, Georgina Basin, Queensland.Alcheringa 11:233–244.

Underwood, C. J. 2002. Sharks, rays and a chimaeroid from the Kim-meridgian (Late Jurassic) of Ringstead, southern England. Palaeon-tology 45:297–325.

Underwood, C. J., and D. J. Ward. 2004. Neoselachian sharks andrays from the British Bathonian (Middle Jurassic). Palaeontology47:447–501.

Velez-Zuazo, X., and I. Agnarsson. 2011. Shark tales: a molecular species-level phylogeny of sharks (Selachimorpha, Chondrichthyes). Molec-ular Phylogenetics and Evolution 58:207–217.

White, E. I. 1968. Devonian fishes of the Mawson-Mulock area, VictoriaLand, Antarctica. Trans-Antarctic Expedition Scientific Reports no.16, Geology 5:1–26.

Winchell, C. J., A. P. Martin, and J. Mallatt. 2004. Phylogeny of elasmo-branchs based on LSU and SSU ribosomal RNA genes. MolecularPhylogenetics and Evolution 31:214–224.

Woodward, A. S. 1888. On the Cretaceous selachian genus Synechodus.Geological Magazine 5:496–499.

Woodward, A. S. 1911. The fossil fishes of the English Chalk.Part 6. Monograph of the Palaeontographical Society 64:185–224.

Yamagishi, H. 2004. Elasmobranch remains from the Taho Limestone(Lower-Middle Triassic) of Ehime Prefecture, Southwest Japan;pp. 565–574 in G. Arratia and A. Tintori (eds.), Mesozoic Fishes3—Systematics, Paleoenvironments and Biodiversity. Verlag Dr.Friedrich Pfeil, Munich.

Submitted August 18, 2011; revisions received October 25, 2011;accepted November 1, 2011.Handling editor: Charlie Underwood.

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