A Lower Carboniferous Xenacanthiform

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A Lower Carboniferous xenacanthiform shark from AustraliaSusan Turnerab; Carole J. Burrowb

a School of Geosciences, Monash University, Victoria 3800, Australia b Queensland Museum,Queensland, Australia

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To cite this Article Turner, Susan and Burrow, Carole J.(2011) 'A Lower Carboniferous xenacanthiform shark fromAustralia', Journal of Vertebrate Paleontology, 31: 2, 241 — 257To link to this Article: DOI: 10.1080/02724634.2011.550359URL: http://dx.doi.org/10.1080/02724634.2011.550359

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Journal of Vertebrate Paleontology 31(2):241–257, March 2011© 2011 by the Society of Vertebrate Paleontology

ARTICLE

A LOWER CARBONIFEROUS XENACANTHIFORM SHARK FROM AUSTRALIA

SUSAN TURNER*,1,2 and CAROLE J. BURROW2

1School of Geosciences, Monash University, Victoria 3800, Australia;2Queensland Museum, Geosciences, 122 Gerler Road, Hendra, Queensland 4011, Australia, [email protected];

[email protected]

ABSTRACT—A new Early Carboniferous (Mississippian, mid-Visean) chondrichthyan, Reginaselache morrisi, n. g., n. sp.,from non- or marginal marine sandy mudstones of the Tetrapod Unit of the mid-Visean (330 Ma = top Holkerian/basalAsbian) Ducabrook Formation, northwest of Springsure, central Queensland, is referred to the order Xenacanthiformes.The taxon is represented by robust diplodont teeth with multicristate cusps, a prominent rounded coronal button, and ahorseshoe-shaped labial boss. Rare spine fragments from the type locality, and a partial lower jaw from a site close by arealso tentatively referred to the taxon. Reginaselache morrisi was a medium-sized, ca. 1 m long shark with numerous teeth,probably feeding on smaller paleoniscoid and other fishes and/or invertebrates. Analysis of the teeth and comparison withthose of other Carboniferous and later Paleozoic xenacanthiforms shows that the tooth cusp morphology is closest to thoseof Triodus Hampe and Bohemiacanthus Schneider. A restricted cladistic analysis of the xenacanthiforms with outgroupsLeonodus Mader, Phoebodus St John and Worthen, and Antarctilamna Young supports the family Diplodoselachidae Hampeas a clade comprising just two genera, Diplodoselache and Reginaselache.

INTRODUCTION

The xenacanthiforms were a successful group of freshwaterand marginal marine sharks during the mid- to late Paleozoic andearly Mesozoic; articulated specimens including embryonic andjuvenile animals are known (Hampe, 2003; Soler-Gijon, 2004).Evidence from older deposits is accumulating to show that theclade was common in shallow-water marine, marginal, and possi-ble freshwater environments (although see Schultze, 2009) andthat at times, they had a global, possibly equatorial, distribu-tion (e.g., Glikman, 1964; Wurdig-Maciel, 1975; Hampe, 1993,2003). From the earliest descriptions (e.g., Agassiz, 1833–1844),xenacanthiforms have been characterized by possession of a dis-tinctive dentition of teeth with two main cusps on a relativelylarge rounded to subrectangular base, the so-called diplodonttype from Diplodus, this original taxonomic name now being de-funct (Zidek, 1993; Turner, 1997; Hampe, 2003).

Xenacanthiform shark remains, especially teeth, are com-monly found in Carboniferous to Permian strata around theworld (Hampe, 1993:fig. 1); possible older records have beenfound in recent years, especially in the Southern Hemisphere.The teeth are now defined as having a tricuspidate crown, withtwo large outer cusps and one or more small or weak (or rarelyabsent) median cusps, and a single lingually extended base. Thedorsal side of the base bears a single coronal button (sometimes‘apical button’ or ‘torus’). On the labial rim of the base there isa single basal protuberance, the ‘boss’ or ‘heel.’ The terminol-ogy used within this paper is based on Hampe (1991, 1994:72,fig. 8).

The earliest articulated Northern Hemisphere xenacanths arefound in the Lower Carboniferous (Visean) (e.g., Dick, 1981),whereas the youngest known are from the Triassic of Europe,U.S.A., India, and Australia (e.g., Turner et al., 2008; Ginter etal., 2010). They have been particularly well studied from coalmeasure basins in Britain (Hampe, 2003) and Germany (e.g.,

*Corresponding author.

Schneider et al., 1988, 2000) and less so from North America,with teeth now used frequently in biostratigraphical studies ineconomically rich basins (e.g., Schneider, 1996, and see below).Hampe (2003:191) considered that xenacanthiforms had a “prac-tically simultaneous appearance in early Palaeozoic deposits ofmarine as well as freshwater environments,” listing the Early Car-boniferous (Visean) Diplodoselache Dick, 1981, from Scotland asthe oldest taxon. However, he did not discuss older Australianand North American records of isolated teeth (e.g., Turner,1993), with one (Turner, 1982; Burrow et al., 2010) referredto Xenacanthus and other examples thought to be cf. Diplo-doselache, but with some resemblance to those of HagenoselacheHampe and Heidtke, 1997, from Germany (Turner, 1993).

Previously Hampe (1993) had doubted the existence of Devo-nian xenacanthiforms, although a cladistic analysis by Hampe andLong (1999:fig. 6) based on teeth, spines, and scales concludedthat Antarctilamna Young, 1982 (mid-Devonian, E Gondwana),was the sister group of the clade. Antarctilamna is now placed inits own family and considered to be a senior synonym of Wellero-dus, known from isolated mid- to Late Devonian teeth in theU.S.A. and Spain (Turner, 1997; Ginter et al., 2006, 2008, 2010).A series of xenacanthiform taxa in the Late Devonian to EarlyCarboniferous of the Southern Hemisphere (Silva Santos andSalgado Carvalho, 1970; Mensah, 1973; Oelofsen, 1981; Turner,1982, 1993; Long and Young, 1995; Garvey and Turner, 2006)shows the teeth are found typically in association with a faunaincluding hybodontiform sharks (e.g., Dick, 1976; Turner, 1993),gyracanthids (Turner et al., 2005), and often tetrapods (Turner etal., 1996). The stepwise stratigraphical and geographical distribu-tion of xenacanthiforms seems to be related to the Laurentian-Gondwana collision (see below).

Only a few Early Carboniferous xenacanthiform taxa havebeen formally described based on teeth, with others notedin open nomenclature. Specimens found in the 19th cen-tury were assigned to Diplodus minutus (figured by Agassiz,1843), and Diplodus parvulus, Dicentrodus (Cladodus) bicusp-idatus, and Xenacanthus (Pleuracanthus) elegans described by

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Traquair (1881, 1888, 1903; see Hampe, 1999, 2003). Dick (1981)described the articulated Diplodoselache woodi, and Hampeet al. (2006) reported on Dicentrodus sp. teeth from Iowa, U.S.A.Turner (1982, 1993) and Lebedev (1996) recorded xenacanthi-form Diplodoselache-like teeth in the late Tournaisian to earlyVisean of Australia and Tournaisian of Russia. A single spinewas described as Xenacanthus tocantinsensis Silva Santos and Sal-gado Carvalho, 1970, from the Lower Carboniferous Poti Forma-tion of northern Brazil, then the oldest xenacanthiform. Turner(1982:fig. 8K; Burrow et al., 2010:fig. 6S) illustrated an older toothfrom the basal Carboniferous of Queensland.

The Middle Paddock site (mid-Visean Ducabrook Formation)in central Queensland, eastern Australia, has yielded the firstCarboniferous tetrapod remains from the Southern Hemisphere(Thulborn et al., 1996; Warren and Turner, 1999, 2004; Warren,2007; see these references for locality information and maps);macro- and microremains of fishes (Turner et al., 1999); gyracan-thid acanthodian remains (Turner et al., 2005); scales and bonesfrom paleoniscoids, rhizodonts (Turner et al., 1996; Johansonet al., 2000; Parker et al., 2005); lungfish (Turner et al., 1999;Kemp, 2001); and shark material including Ageleodus teeth, hy-bodont spines, and possible scales, as well as the xenacanthiformremains described below.

This paper describes the new xenacanthiform material fromMiddle Paddock, comparing it with teeth from the earlier Nar-rien and Raymond formations of Queensland as well as with taxafrom elsewhere.

Institutional Abbreviations—ANSP, Academy of NaturalSciences Museum, Philadelphia; NHMUK PV P, The NaturalHistory Museum, London; FMNH PF, Field Museum of NaturalHistory, Chicago; QMF, Queensland Museum Fossil collection,Hendra, Brisbane.

GEOLOGICAL SETTING

The Drummond Basin in east-central Queensland constitutes adiscrete Upper Devonian–Lower Carboniferous depositional en-tity, the mostly undeformed sediments of which are exposed overabout 25,000 km2 (Veevers, 2000:figs. 79, 260). In Late Devo-nian to Early Carboniferous (Mississippian) times it was an inter-montaine basin, receiving up to 12,000 m of mainly fluviatile andlacustrine sediments via a northward drainage system (Olgers,1972) with shallow-marine incursions from the northeast (Veev-ers et al., 1984; Day et al., 1983). Within the basin, apart fromthe one tetrapod-bearing member mentioned above, fish havebeen found in marginal to non-marine sediments in the UpperTelemon, Raymond, Ducabrook, Star of Hope, and Bulliwallahformations. Turner (1982, 1993) and Fox et al. (1995) estimatedthe age of the Raymond Formation vertebrate-bearing strata asearly to mid-Visean. The younger Bulliwallah Formation is ex-posed in the northern basin (Turner and Cook, 1999; Burrow,2004; Turner et al., 2005), with the contemporaneous DucabrookFormation exposed mainly in the southern part.

The new xenacanthiform elements were found in the Tetra-pod Unit and age-equivalent rocks of the Ducabrook Forma-tion, a thick (>2100 m) sequence of interbedded sandstones andmudstones, predominantly khaki-brown and olive-green in color,with occasional beds of conglomerate, tuff, oolitic limestone, andstrings of algal nodules and vertebrate debris (Mollan et al., 1969;Olgers, 1972). The sediments probably accumulated in shallowmarginal, lagoonal, fluviatile, and lacustrine settings on a flood-plain, and, before discovery of tetrapod material at the MiddlePaddock locality QML1117 in 1995, had yielded paleoniscoids(“Elonichthys”) (Hill and Woods, 1964; Turner and Long, 1987)and occasional acanthodian spines (Gyracanthides) (Turneret al., 2005). Some material described here was obtained fromcorrelatable beds on the adjacent Mowbray Station.

Turner et al. (1999) interpreted the poorly bedded andsorted sediment with comminuted plant remains characterizingQML1117 as a possible storm deposit. Latterly, Parker and Webb(2008) ascribed the Tetrapod Unit at QML1117 to their ‘Lime-Flake Facies,’ deposited during a storm-induced flood event ontothe tidal channel floor in an estuarine environment. Taphonomi-cally, the vertebrate remains occur in beds about 1 m in thicknessand although sometimes concentrated in one area (see commentsbelow), specimens appear to be randomly oriented.

In addition to vertebrates, branchiopods (Leaia), plant macro-fossils of the Lepidodendron flora (White, 1972), and a richpalynoflora indicative of mid-Visean age occur within the for-mation (Veevers, 2000). From a nearby GSQ drill core, Playford(1977) recorded prolific miospores of Granulatisporites frusulen-tus, a taxon found in the Famennian to Visean of Australia, andbased on the palynoflora gave a Visean age (Jones, 1996; Joneset al., 2000). The Ducabrook Formation is dated as mid-Visean(ca. 333–335 Ma), equivalent to basal Asbian (V3b) (Heckel andClayton, 2006), based on recognition of the Anapiculatisporiteslargus Assemblage (Jones and Truswell, 1992; Jones et al., 2000).The general faunal assemblage and paleoenvironments of the de-posits closely resemble the tetrapod-bearing sequences in south-eastern Scotland (Wood and Rolfe, 1985; Turner et al., 1999).

MATERIALS AND METHODS

The vertebrate locality, QM L1117, consists of grey-green fri-able to indurated sandstone with small to microscopic orange-brown rounded pebbles. The site was reported to the QueenslandMuseum in late 1995 and a preliminary field trip confirmed thepresence of tetrapods as well as fish taxa (Thulborn et al., 1996).Xenacanthiform teeth were first found scattered on the surfaceand collected by Mr. Morris Hawkins in an area that we subse-quently called ‘Morris’s Mound.’ The teeth were reported to mu-seum staff during the first major field trip at Easter 1996 whensamples of all rock types exposed and bones and teeth were col-lected from the surface (Turner et al., 1996, 1999). Material col-lected on this and subsequent field trips has produced more than120 xenacanthiform teeth and rare spine fragments from surfacecollecting, excavation of the main bone-bearing horizon, as wellas breakdown of rock with subsequent picking in the laboratory,smaller specimens, broken cusps, and separate bases mostly be-ing found in sieved residues. The jaw fragment QM37521 was col-lected in 2004 by Carl and Joan van der Smissen from a localitysouth of QM L1117, adjacent to Snake Range National Park.

Manual preparation and freeing of exposed xenacanthiformteeth from the sediment was done using sharp needles. As thecusps are particularly vulnerable, specimens were often coatedwith paraloid or Mowitol. To uncover teeth in the sandy mud-stone, blocks were first immersed in water, then cooked in a mi-crowave oven for 2–3-minute sessions. Muddy residue was de-canted, washed through a 0.1-mm sieve, dried, then picked withbrush or needles under a binocular microscope. Scanning elec-tron microscope (SEM) images of the uncoated holotype toothwere produced using an Hitachi TM-1000 Tabletop ESEM; otherteeth were coated with platinum and imaged using a Jeol JSM-6300F Scanning Electron Microscope; ground thin sections wereimaged using an Olympus BX-50 transmission microscope andDP-12 imaging system; larger images were taken using an Olym-pus SZ40 dissecting microscope and DP-12 imaging system or aNikon Coolpix 995; figures were compiled using Adobe Photo-shop.

SYSTEMATIC PALEONTOLOGY

Class CHONDRICHTHYES Huxley, 1880Subclass ELASMOBRANCHII Bonaparte, 1832

Order XENACANTHIFORMES Berg, 1940Family DIPLODOSELACHIDAE Hampe, 2003


TURNER AND BURROW—CARBONIFEROUS XENACANTHIFORM SHARK 243

FIGURE 1. Reginaselache morrisi, gen. et sp. nov., holotype, tooth QMF39642. A–C, laterolingual view, with B, closeup view of cusp showing wavy,branching cristae, and C, closeup of heavily pitted button and base surface; D, E, labiobasal view, with closeup of median cusp in E; F–H, occlusalview, with closeup of larger curved cusp and small median cusp in G, and of button in H. All scale bars equal 1 mm.

Remarks—Hampe (2003) revised the diagnosis for xenacan-thiform families, unifying the basal genera (Diplodoselache, Di-centrodus, Lebachacanthus, Orthacanthus, and Hagenoselache)in one family, the Diplodoselachidae. His revised diagnosis didnot include tooth characters, and his cladistic analysis of the or-der shows the group as a grade rather than a clade (Hampe,2003:fig. 24). A new cladistic analysis (see below) indicates thatDiplodoselache and Reginaselache form a poorly supported sistergroup to other xenacanthiforms.

Genus REGINASELACHE, gen. nov.

Type Species—Reginaselache morrisiDiagnosis—As for type and only species.Etymology—From the Latin, regina, a queen—in allusion to its

place of discovery, Queensland, and selache, a shark.

REGINASELACHE MORRISI, sp. nov.(Figs. 1–4A—M, 5, 8A)

cf. Diplodoselache woodi: Turner et al., 1996:69A.“Xenacanth”: Turner et al., 1999:178.“Xenacanths”: Johanson et al., 2000:168.“A new species of xenacanthidid”: Warren and Turner, 2004:155.“A new xenacanthiform”: Turner et al., 2005:964.“Shark”: in part, Parker and Webb, 2008:table 2.

Holotype—Tooth QMF39642 (Figs. 1, 8A).Other Referred Materials—Paratypes are ca. 120 teeth,

isolated cusps, and thin sections of teeth including fig-ured specimens QMF39599–39618, 39621–39623, 39648, 39649(Figs. 2A–V, 3, 4A–M, 5); unfigured specimens QMF37392,

QMF39627–39629, 39633–39641, 39643, 39645–39647; and teethincluding QMF39644 from nearby Mowbray Station.

Other materials including spine fragments, scales, and a lowerjaw are tentatively assigned to this species (see below).

Type Locality and Stratigraphy—Middle Paddock, QM L1117(details of site kept by the Queensland Museum), DucabrookStation near Springsure, central Queensland; Tetrapod Unit,Ducabrook Formation; Mississippian, mid-Visean (see above).

Diagnosis—Xenacanthiform with presumed dorsal spine, andnumerous small to medium-sized teeth 1.5–8.5 mm high, slightlyasymmetrical with one of two major cusps being thicker than theother; all cusps with subcircular parabasal section and no lateralcarinae; two lateral (main) cusps with five to six wavy cristae onlabial side of cusp and up to 20 cristae in total; cristae extendingfrom cusp apex down almost to cusp/base interface, some branch-ing towards base; median cusp not greater than half main cuspheight, set slightly labiad; angle between teeth and base ca. 100◦;large rounded high coronal button separated from cusps, posi-tioned in center of dorsolingual base surface, occasionally con-nected to region of median cusp by narrow ridge; several foram-ina, fewer than five, around base of coronal button; base extendslingually beyond coronal button; base robust, circular to heart-shaped or subtriangular outline; basal tubercle prominent andmore or less equal to height of base, ventrally expressed as a widehorseshoe shape; basal surface with central depression, often withwide groove leading to midpoint of lingual edge; vascular canalforamina large, with no uniform pattern except around edge ofbasal concavity or lingual to labial boss surface; one large fora-men usually in center of basal depression, with less than five otherforamina around edge of central concavity.



FIGURE 2. Reginaselache morrisi, gen. et sp. nov., teeth. A–E, QMF39599 in laterocrown, lateral, labiolateral, laterobasal, and closeup of cusptip views; F–J, QMF39600 in labial, lateral, linguolateral, labiolateral, and closeup of cusp tip views; K–N, QMF39601 in crown, closeup of mediancusp base, anterocrown, and laterocrown views; O, P, QMF39602 in anterocrown and crown views; Q, QMF39603 in crown view; R, QMF39604 inlaterocrown view; S, T, QMF39605 in basal and lateral views; U, V, QMF39606 in basal and laterobasal views. Scale bar equals 1 mm in A–D, F–I, K,M, N–V, and 0.1 mm in E, J, L. All images are SEMs except F, which was taken in normal light before the tooth was extracted from the matrix andthe median cusp lost; the image was equalized in Photoshop for better contrast.



FIGURE 3. Reginaselache morrisi, gen. etsp. nov., teeth. A–D, QMF39607 in latero-labiobasal, basal, labiobasal, and lateral views,respectively; E, F, QMF39608 in occlusal andbasal views; G, H, QMF39609 in occlusal andbasal views; I, J, QMF39610 in occlusal andbasal views. All scale bars equal 1 mm; sketchesB, D not to scale. All drawings ©Dr. S. Turner.

Etymology—morrisi, for Mr. Morris Hawkins of centralQueensland, the first collector of the material.

Description

Tooth Morphology—The teeth range in size from 1.5 to8.5 mm high and wide. Nearly all teeth are tricuspid and slightlyasymmetrical, with one main cusp slightly larger and thicker thanthe other (Figs. 1F, 2C, K, O, Q, 3A, C). Preservation variesfrom good with sharp cristae on the cusps to very worn (Fig.2Q) with almost smooth shiny cusp surfaces, and color variesfrom light brown to orange to dark brown to black. The smallerlateral cusp is straighter, almost vertical to the base, with thelarger cusp curving slightly away laterally. Isolated broken cusps,which when only one is detached is usually the shorter of thetwo, are identifiable by shape and surface ornament. The smallmedian cusp, rarely up to half the height of the larger cusps(Figs. 1, 2B–C, F, 3G) and usually present through the toothsize range but often broken off, is set slightly labiad to the maincusps.

The teeth bear numerous (8–20) cristae on the two main cusps,extending almost to their bases, with no lateral carinae. The cuspsare usually subcircular in cross-section (Figs. 2K, Q, 4A, D), butcan be ovoid to subrhombic. The large prominent rounded but-ton on the dorsolingual basal surface is separated from the cuspsin most specimens (Figs. 1, 2A, G, K, P, Q, R); in a few, there is anarrow median shaft connecting the coronal button to the mediancusp. The button is up to 2.5 mm high, with a small number offoramina around its rim (Figs. 1H, 2A, Q). The base extends lin-gually beyond the button and, labiolingually, the outline is ovoidto heart-shaped (Figs. 2K, M, S, 3A, B) with a rounded rim and afew large foramina. The ventral undersurface of the base is con-cave, with in most specimens a large centrally placed foramenopening into the concavity (Fig. 2T–V). On the mid-ventral rimof the labial surface there is a prominent basal boss with a distinc-tive horseshoe shape that extends into the central basal depres-sion (Figs. 2D, S–V).

The holotype QMF39642 (Figs. 1A–H; 8A) is 3.0 mm deeplabiolingually, 6.0 mm high, and 3.0 mm wide, with both lateralcusps intact but fractured and 0.7 mm of smooth median cusppreserved (Fig. 1E). Each lateral cusp has ca.10–12 cristae, sev-eral of which branch close to the cusp base (Fig. 1B). The coronalbutton is rounded and heavily pitted, as is the rest of the uppersurface of the base (Fig. 1C, H).

A typical tooth QMF39599 (Fig. 2A–E) is 4.5 mm deep, 4.5 mmhigh, and 4.0 mm wide at the base of the cusps, with a roundedcoronal button, horseshoe-shaped basal boss, ovoid base outline,and a medial notch on the lingual edge. Although multiply frac-tured, both main cusps and a central cusp are preserved. Maincusps have ca. 16 well-preserved, wavy vertical cristae, and worntips; the central cusp is relatively robust and 1.5 mm high.

One of the smallest teeth QMF39601 (Fig. 2K–N) is 1.5 mmhigh and wide, and 2 mm deep labiolingually. The main cusptips and median cusp have broken off; all three have a circularparabasal section. Cristae are sharp, with each main cusp havingca. 10 extending down to the cusp base. One relatively large fora-men opens out on the lingual face of the round coronal button.QMF39607 (Fig. 3A–D) has at least six, probably seven to eight,fine but prominent cristae on the cusps, with one ending abouthalf way up almost coalescing with another crista. Cristae can beof slightly different length, and not always parallel (e.g., Figs. 2B,H, K, 4B, C, F, H–J, M), with some more sinuous. QMF39614(Fig. 4E) is a 2.5-mm-high cusp from a mid-sized tooth, also withsharp cristae extending almost to cusp base. QMF39615 (Fig.4F–G) is an isolated cusp from a small tooth, with sharp cristaebut a worn and rounded tip.

Largest teeth are ≥5 mm wide, ≥5–5.5 mm labiolingual baselength, and ≥5 mm high, e.g., QMF 39608–39610 (Fig. 3E–H).QMF39608 (Fig. 3E, F) has one cusp base intact, with onebroken and a part-depressed fracture, and a small, elongatedcentral cusp. This specimen shows clearly the basal and side con-figuration, the coronal button separated from the cusps, high androunded and placed in the center of the dorsolingual base. Themain cusps are subrectangular, and five or more cristae on thelabial surface of the broken cusp that do not quite reach to the



FIGURE 4. Reginaselache morrisi, gen. et sp. nov., tooth cusps and possible scales. A, B, loose cusp QMF39611 in apical and lateral views; C, cuspQMF39612 in lateral view; D, broken cusp QMF39613 in apical view; E, loose cusp QMF39614 in lateral view; F, G, loose cusp QMF39615 in lateraland closeup views; H, loose cusp QMF39616 in lateral view; I, J, loose cusp QMF39617 in lateral and apicolateral views; K–M, broken, squashed cuspQMF39618 in ?lingual, apicolateral, and apical views. ?Reginaselache morrisi N, scale QMF39619, in crown view; O, scale QMF39620, in lateral view.Scale bar equals 1 mm in A–E, K–M, and 0.1 mm in F–J, N, O.

cusp/base interface. There is a short apron below the shiny partof the cusp, which presumably was covered in life with epithe-lium. On QMF39609 (Fig. 3G, H), which measures 6.5 mm ×7.5 mm, the base is rather worn, exhibiting a medial groove inthe basal concavity. The midpoint of the lingual edge can bedeeply notched with a corresponding groove on the undersideof the base leading into the central depression (e.g., QMF39608;Fig. 3F). QMF39610 (Fig. 3I, J) has a well-preserved tumid baseand a large asymmetric, tumid labial boss; both cusps have well-preserved ornament but broken tips.

Tooth Histology—Thin sections (Fig. 5) show that the cuspsare composed of an outer relatively shiny orthodentine layer withvery fine dentine tubules branching near the outer surface (Fig.5D–F) and an inner core of trabecular dentine ( = osteodentine).Although Hampe (2003) stated that all xenacanthid teeth lackenameloid, a thin outer layer of clear tissue appears to be presentin Reginaselache morrisi in some areas (Fig. 5A, B, D–G). How-

ever, the layer is not birefringent under polarized light and hencelacks the oriented crystals that typify enameloid (and enamel)and thus this tissue is akin to that called ‘durodentine’ (e.g.,Gross, 1967). The basal tissue is trabecular dentine with a fewlarge canals that penetrate the base with large foramina. Thecoronal button is also formed of trabecular dentine with large,mainly transverse canals, and is separated from the basal tissueby a thin layer of orthodentine (Fig. 5C, H, I).

Tooth Pathology—Hampe (1997) discussed anomalous growthforms in xenacanthiform teeth, and rare teeth of Reginaselacheshow evidence of one or two minute cusps between the me-dian and lateral cusps (Fig. 2I, Q, R), indicative of minordevelopmental anomalies. One isolated cusp (Fig. 4K–M) seemsto have been crushed before fossilization. Hampe (1997) did notreport wear on cusp tips in xenacanthiform genera, whereas sev-eral teeth of Reginaselache have cusp tips that have been roundedoff and worn down, often with the cristae also worn off well



FIGURE 5. Reginaselache morrisi, gen. et sp. nov., thin sections of teeth. A, QMF39648, cross-section of lateral tooth tip under blue light excitation,showing growth lines in orthodentine; B, QMF39623, slightly more basal cross-section of a tooth cusp; C, D, I, vertical labiolingual section of toothQMF39621 showing C, the whole section, D, closeup in polarized light of segment indicated by arrow in C, I, closeup of the structure of the button;E–G, cross-section of tooth cusp base QMF39622, E showing nearly the whole section, F a closeup of section with a crista, and G the same closeup inpolarized light; H, QMF39649, horizontal section of base, labial edge at bottom, under blue light excitation, showing osteodentine/trabecular dentinewith orthodentine layer around lateral and labial margins of the lateral cusps, but not in the base of the central cusp?. Arrows indicate approximatelevels of cross-sections. Scale bar equals 1 mm in C, E, 0.1 mm in B, D, I.



below the tip (e.g., Figs. 2E, J, N, 4F, J). These teeth have notbeen broken either mortem or postmortem, during burial, or dur-ing discovery or preparation but seem to have undergone wearduring life (see discussion below).

?REGINASELACHE MORRISI(Figs 4N, O, 6–7)

Remarks—Although all the teeth recovered from the locali-ties are deemed to be from one species, and it is unlikely that the

other xenacanthiform elements are from a different species, be-cause we have not found the spines and other material in articula-tion with the teeth, we have only tentatively assigned these otherelements to R. morrisi. For the purpose of analysis, however, wehave treated all as one taxon (see below).

Materials—Scales QMF39619, 39620 (Fig. 4N, O); dorsal spinefragments QMF39624, 39625, 39630, 39631 (Fig. 6 A–J), and39632 from QM L1117; the posterior half of a lower jawQMF37521 (Fig. 7) from a locality near the Snake Range NP.

FIGURE 6. ?Reginaselache morrisi, gen. et sp. nov., fin spine fragments. A–C, spine tip QMF39624.a in lateral (leading edge up), trailing edge, andlateral (leading edge down) views; D, longitudinal section QMF39624.b through one side of a more proximal fragment of the same spine (leadingedge up, through bases of denticles); E, transverse section QMF39624.c through another more proximal fragment; F, G, spine tip QMF39625 in lateral(leading edge up) and trailing edge views. H–K, spine QMF39631, preserved as proximal leading or trailing edge fragmented piece (removed frommatrix) plus mid to distal segment, and impression of distal tip in matrix (H); I, proximal end of main segment; J, closeup of denticles; K, distal end ofmain segment. Scale bar equals 1 mm in A–E, 10 mm in F–K. Abbreviation: dr, denticle row.



FIGURE 7. ?Reginaselache morrisi, gen. et sp. nov., partial lower jawQMF37521. A, lateral view, anterior to left; B, medial view; C, occlusalview. Scale bar equals 10 mm.

Description

Scales—Scales found at the type locality that might be fromReginaselache morrisi are robust, thick-based rhombic scales sim-ilar to those of Holmesella Gunnell, 1931. They are ca. 1.5 mmwide and high, often with only the tumid base and a worn rem-nant of the crown preserved. Two scales only have been recov-ered with well-preserved crowns (Fig. 4N, O). Histology is thesame as that in Holmesella (Zangerl, 1968:fig. 2G) and Protacro-dus (Gross, 1973:figs. 27, 28), with a crown having centrifugallyarranged, apposed growth zones composed of orthodentine, onan acellular lamellar bone base.

Spine Morphology—All fragments are symmetrical and haverough, narrow, closely spaced ridges running longitudinally.QMF39624.a (Fig. 6A–C) and QMF39625 (Fig. 6F, G) are dis-tal tip fragments each ca. 20 mm long, with a double row of ca.1 mm denticles along the presumed posterior or trailing edge,closely spaced at seven denticles per centimeter in each row. Onlythe bases of the denticles are preserved, with all projecting apicesbroken off.

The largest preserved specimen is QMF39631 (Fig. 6H–K),with an estimated length of 100 mm. The spine fragments com-prise the mid 50 mm, plus the impression of one side of the moredistal 5 mm, and the trailing or leading half of the proximal end(Fig. 6H). The rounded impression of the distal end indicates thedistal spine tip was broken off and worn down in life, or at leastbefore fossilization. The spine is laterally flattened; maximumdepth 10 mm and width 5 mm, both near the middle of thespine, which tapers towards distal and proximal ends (Fig. 6I, J).Narrow, irregularly arranged but longitudinal ridges separatedby narrower grooves cover the whole spine. Two rows of smooth,recurved pointed denticles extend for the distal-most 15 mm,oriented posteriorly (cf. life position of spines) along each sideof the trailing edge; some denticles are preserved (Fig. 6K), butmost are represented only by their bases, with the rest brokenoff during collection/preparation.

Spine Histology—External longitudinal ridges and denticlesare formed of osteodentine; no dentine tubules are visible in thebases of denticles cut through in longitudinal section (Fig. 6D).Small fragments broken off from QMF39624 show that the inter-nal structure is wholly composed of a highly trabecular osteoden-tine (Fig. 6D, E). There is no evidence of an outer enameloid ororthodentine layer.

Remarks—Assuming that all fragments are from the samespecies, the largest spines must have been at least 100 mm long inlife, denticulated only along the distal quarter or less. Given thefamily assignment, the dorsal spine in Reginaselache would havebeen placed anterior to the dorsal fin rather than on the back ortop of the head as in more advanced xenacanthidids (e.g., Soler-Gijon, 1997:fig. 6).

Lower Jaw Fragment—Specimen QMF37521 (Fig. 7A–C) isthe posterior two-thirds of a robust, heavily calcified Meckel’scartilage; total length is 105 mm. At the anterior fracture surfacethe jaw is 25 mm deep, and 30 mm at its deepest just anterior tothe shelf that is presumed to demark the lower limit of the dentallamina. The ventral edge is slightly convex and thickened, curvingmore tightly posteriorly and forming a flange behind the circulararticular cotylus. A shallow groove for the adductor muscle ex-tends from the anterior limit of the cotylus to the buttress runningup from the ventral edge, at the front of the flange. The dorsaledge of the jaw bulges upwards in front of the cotylus to form anarticulatory surface, a feature referred to by Ginter and Maisey(2007) as a mandibular knob, which slotted into a quadrate con-cavity on the palatoquadrate. The dorsal edge flattens out in frontof the knob to form a slightly concave shelf medially, under whichthe ceratohyal is presumed to have lain. The shelf fades out nearthe end of a low ridge that extends forward from the shelf alongthe middle of the medial face of the jaw. This ridge probably rep-resents the base of a shallow, featureless dental groove. No ev-idence is preserved of the position of the dental families on thejaw.

COMPARISON

Hampe (1999, 2003) revised the British Lower Carboniferoustaxa, enabling a detailed assessment of the relationship betweenDiplodoselache, the new Australian taxon, and other xenacanthtaxa. Thus we can compare Reginaselache morrisi with theoldest known articulated xenacanthiform Diplodoselache woodifrom the contemporaneous Visean Lower Oil Shale Groupof Scotland (Fig. 11). Diplodoselache woodi has numeroussmall bicuspid teeth (Dick, 1981:fig. 12) of the type first figuredby Agassiz (“Diplodus minutus” in 1833–1844:v. 3, table 22b,figs. 6–8; listed as nomen nudum because the specimens wereincomplete and are now lost) from the Burdiehouse Limestone(Hampe, 2003). Agassiz did not record a median cuspule in theseteeth. The Middle Paddock teeth show the same size range (1–8mm) as those described by Agassiz. “Diplodus” was recordedalso from younger horizons including the Blackband Ironstoneof the Burghlee (or Borough Lee) Limestone (Limestone CoalGroup) and the South Parrot Coal (Upper Limestone GroupB-P1) (e.g., Traquair, 1881, 1903, 1905) and Gilmerton (Dick,1981), but there is no clear idea given in these papers of cuspornament or of basal configuration; such characters were rarelyidentified by earlier workers. The somewhat similar teeth fromthe Visean Borough Lee Ironstone, for which Traquair (1881:36)erected “Diplodus parvulus,” have a median cuspule—“a smallboss or knob which is frequently divided or notched into severalminute rounded lobules,” a carina that runs up the labial marginof the base ending on this knob, and tooth cusps that also bearcarinae or ridges towards their apices (Hampe, 2003:fig. 6).This taxon, which Hampe (2003) reassigned to Diplodoselacheparvulus, is recorded from several sites in eastern Scotland,including Borough Lee and Pitcorthie (Hampe, 2003). Hampe



FIGURE 8. Drawings of teeth from Reginaselache and other xenacanthiform genera, showing specimens from type species where possible; lingualviews unless noted. A, Reginaselache morrisi holotype, lateral view; B, Diplodoselache woodi (Hampe, 2003:fig. 4a); C, Dicentrodus bicuspidatus(Hampe, 2003:fig. 8a); D, Hagenoselache sippeli, lateral view and coronal view of isolated base (Hampe and Heidtke, 1997:fig. 4B, C); E, Lebachacan-thus senkenbergianus (Soler-Gijon, 1997:fig. 2 in part; as far as we are aware, no detailed drawings of Lebachacanthus teeth have been published); F,Wurdigneria obliterata, lingual and lateral views (Richter, 2005:fig. 10C, D); G, Triodus sessilis (Heidtke et al., 2004:fig. 6b); H, Orthacanthus gibbosus(Hampe, 2003:fig. 9b); I, Xenacanthus laevissimus (Hampe, 2003:fig. 15a); J, Bohemiacanthus sp. (after Schneider, 1988:fig. 1); K, Plicatodus plicatus(Hampe, 1997:fig. 1). All scale bars equal 10 mm.

et al. (2006:fig. 3) gave the stratigraphic ranges of Scottish EarlyCarboniferous xenacanthiform taxa (cf. Fig. 11).

Diplodoselache woodi teeth (Dick 1981:fig. 12) have a cen-trally placed coronal button and a small central cusp, with main

FIGURE 9. Cladistic analysis of outgroups Leonodus, Antarctilamna,and Phoebodus, and xenacanthiform genera represented by teeth plusother elements. As only 11 taxa were thus included, an ACCTRANbranch-and-bound search was undertaken using PAUP 4.0b10 (Swofford,2002), all 19 characters unordered and of equal weight; multistate taxawere treated as uncertainty. The single shortest most parsimonious treeis 40 steps, CI = 0.7750, RI = 0.7632. Changes at nodes are listed inAppendix 2.

cusps that are laterally compressed, sharply carinate but other-wise smooth (Fig. 8B); the Ducabrook teeth differ in all thesecharacters. Of the other non-xenacanthid genera, Dicentrodusdiffers from Reginaselache by having extremely asymmetricalteeth with a flat base and divergent main cusps with a lanceo-late cross-section and finely serrated edges (Hampe et al., 2006;Figs. 8C, 10E, F); Orthacanthus teeth always have a minute me-dian cusp, some serrations on the main cusps, and a basal tuber-cle without a concave depression (e.g., Hampe, 2003; Fig. 8H);Lebachacanthus Soler-Gijon, 1997, teeth have massive, serratedmain cusps (Hampe, 2003; Fig. 8E); and Hagenoselache teeth aresmall (less than 3.5 mm) with their median cusp 3/4 or 4/5 theheight of the main cusps, and the angle between crown and base120–125◦ (Hampe and Heidtke, 1997; Fig. 8D). The other de-scribed xenacanthiform taxa from Gondwana is the younger Per-mian Wurdigneria (Richter, 2005; Fig. 8F); the teeth are robustbut have smooth cusps with only a lateral carina and no cristae.

The older xenacanthiform teeth from the nearby NarrienRange (Turner, 1993:fig. 4C–G) resemble more closely those ofHagenoselache sippeli Hampe and Heidtke, 1997, from the Na-murian B of Germany. The teeth of Reginaselache show someof the diagnostic characters of the Xenacanthidae as revised byHampe (2003), most closely resembling those of Triodus (andBohemiacanthus Schneider, 1996, if this is a valid genus) but dif-fering in having slightly sinuous cristae that extend from the tipto close to the base of the main cusps, and in the histologicalstructure of coronal button and underlying base. The Permianxenacanthid Plicatodus is the only other xenacanthiform to havewavy cristae on the main cusps, but its teeth have a flat base, manynutrient foramina, and a small flat coronal button (Hampe, 2003).

The spine fragments referred here to Reginaselache are com-patible with assignment to a xenacanthiform shark in having adouble row of posterior denticles, lacking a posterior groove,and being wholly composed of osteodentine. The rough ridgesforming the outer surface of the spines are comparable to the“bark-like ornamentation” described for Diplodoselache woodi(Hampe, 2003:199, fig. 4k) rather than the smoother and/or more



FIGURE 10. Late Devonian and Early Carboniferous xenacanthiform teeth, some not yet assigned to species. A–D, Diplodoselache-like toothQMF13391, Tournaisian Telemon Formation, Narrien Range, central Queensland (ST drawings) in A, lingual view; B, occlusal view; C, lateral view;D, labiobasal view. E–H Dicentrodus sp. 1A FMNH PS-14028a, Heimstra Quarry, near Delta, Iowa (ST drawings), in E, lingual view; F, lateral views;G, labial view; H, basal view. I, xenacanthiform tooth ANSP 23232, mid-Famennian of Red Hill, Pennsylvania, in labial view. J, K, Diplodoselache?antiqua (Lebedev 1996:fig. 9b, d), Tournaisian of Tula, Moscow Basin. L, M, JHQ-09 xenacanthid? tooth FMNH (PF15378) from the mid-ViseanUpper St Louis Formation, Heimstra Quarry, Delta, Iowa. Scale bar equals 0.1 mm in L, M; 0.5 mm in E–G; 1 mm in A–D, H, I.

finely ribbed Xenacanthus and Orthacanthus spines (Soler-Gijon,2000; Soler-Gijon and Siebert, 2001). The dorsal spine on Diplo-doselache woodi (NMS 1974.51.4), which lies near the front ofthe dorsal fin approximately half way between the level of thepectoral and pelvic fins, is estimated to have been 75 mm longwith a maximum width of 9 mm (Dick, 1981); the spine onReginaselache was longer and more slender. Hampe (2003:231)grouped the more basal xenacanthiforms in the family Diplo-doselachidae based on the autapomorphic character of “a dorsalspine which always has a rounded cross-section and a ventrallyarranged double row of denticles.” Based on the denticle pat-tern, Reginaselache groups with his diplodoselachids rather thanthe xenacanthids, which have laterally extending posterior denti-cle rows, but differing from all other xenacanthiforms in having alaterally flattened cross-section plus posterior denticle rows.

The lower jaw (Fig. 7) is typical xenacanthiform, with thesecondary ‘articulation’ anterior to the articular cotylus sharedonly by xenacanthiforms and modern elasmobranchs (Ginter andMaisey, 2007). The dental furrow is smooth as in Xenacanthus,rather than subdivided by shallow grooves as in some othergroups of Paleozoic sharks (Dick, 1981). The uncompressed,3D preservation of QMF37521 gives an unequalled view of thestructure of a xenacanthid Meckel’s cartilage. The proportionsof the jaw, by comparison with those of Diplodoselache (e.g.,NMS.GY.1974.51.4 in Dick, 1981:fig. 2), indicate that the wholefish would have been over a metre in length.

The scales tentatively assigned to Reginaselache morrisi are ofthe kind found posterior to the pelvic region on Diplodoselache

(Dick, 1981:fig. 11c). If Reginaselache morrisi also had more frag-ile, thin-based scales similar to those found on the rest of bodyof Diplodoselache (Dick, 1981:fig. 10), it is unlikely that theywould have survived the turbulent depositional environment rep-resented in the type locality.

DISCUSSION

Zidek (1993) recognized dental morphology as a valid crite-rion for distinguishing xenacanthiform species but was doubt-ful regarding the usefulness in defining ‘all’ genera. Schneider(1996), Hampe and Heidtke (1997), and Hampe (2003), for ex-ample, have made it clear that full descriptions of the morpho-logical (Fig. 8) and histological characteristics of teeth do en-able definition of genera. We agree with Schneider (e.g., 1988)that cusp characters can aid in analysis of taxa in combina-tion with tooth base characters. Even though Hampe and Hei-dtke (1997) stressed the number of cristae as an important fac-tor relating Hagenoselache sippeli to Triodus carinatus, Hampe(2003) placed the latter in the Xenacanthidae and the former inthe Diplodoselachidae. Despite some overall similarity, the illus-trated teeth of Hagenoselache have few cristae on the cusps, andthose only close to the tip, so that Reginaselache teeth differ inthat feature. Perhaps the specific tooth morphology, particularlyornament, depends on diet at least as much as on phylogeneticrelationships.

We undertook a cladistic analysis (Appendix 1, Table 1, Fig. 9)of xenacanthiform genera known from more than isolated teeth,



FIGURE 11. Stratigraphical ranges of Early Carboniferous xenacanthi-form taxa (cf. Hampe and Ivanov 2007:fig. 5; extra data from: Garvey andTurner, 2006; Hampe et al., 2006:fig. 3; Ginter et al., 2010; boundary datesfrom Ogg et al., 2008).

using tooth, spine, jaw, and scale characters to test the currentideas of relationship. We revised and extended the list of thesecharacters from the analysis by Hampe (2003:fig. 24), in someinstances reversing character polarity based on our interpreta-tion that the diplodont, rather than the cladodont, tooth form isplesiomorphous for xenacanthiform lineage (Appendix 1). TheDevonian genera Leonodus Mader, 1986, Antarctilamna Young,1982, and Phoebodus St John and Worthen, 1875, which also have‘diplodont’ teeth and have often been compared with xenacanthi-forms (e.g., Ginter, 2004), were used as outgroups. Botella et al.(2005, 2009) investigated the histological structure of the cuspson Leonodus teeth; Botella (pers. comm., 2010) has advised that

the button area is composed of the same trabecular osteodentineas forms the rest of the base.

In the resulting cladogram, the xenacanthiforms are unitedby five characters (see Appendix 2), and within the xenacanthi-forms, Diplodoselache and Reginaselache form a sister group tothe other genera, although the node supporting their relationshipis only poorly supported (Appendix 2), with the single synapo-morphy being the coronal button composition. Nevertheless, wetentatively refer Reginaselache to the family Diplodoselachidae,with Diplodoselache as the only other genus included. Our anal-ysis indicates that Hagenoselache, Plicatodus, Triodus, and Xe-nacanthus form a better-supported clade. The node uniting theother xenacanthiform genera is more strongly supported, as is thefamily Xenacanthidae (Appendix 2).

Paleobiogeography

In Australia we now have found xenacanthiform teeth in-cluding Reginaselache and cf. Diplodoselache (Fig. 11) in theEarly Carboniferous (e.g., Turner, 1982, 1993; Jones et al., 2000)from at least four horizons spanning the basal Tournaisian tomid-Visean in the Drummond Basin; a small tooth from one ofthe basal beds in the Telemon Formation is shown here (Fig.10A–D).

Small (microscopic <5 mm) xenacanthiform teeth have alsobeen noted in the Famennian Red Hill fauna of Pennsylvania(S.T., pers. observ., 2001; Fig. 10I); in the possible D/C boundarybeds of Mansfield, Victoria (Long in Garvey and Turner, 2006);and in the basal Tournaisian of Horton Bluff, Nova Scotia (S.T.,pers. observ.).

Turner (1993) described the chondrichthyan assemblage ofthe Raymond Formation, underlying the Ducabrook Formation,which contains a closely similar fauna to that from the Scot-tish Lower Carboniferous (early to mid-Visean) at least at thegeneric level and compared the xenacanthiform teeth to thoseof Diplodoselache as illustrated by Dick (1981). Based on a sur-vey of North American, some 50 Scottish, and the Queenslandsites, she defined an Ageleodus-xenacanthiform-hybodontiform(Tristichius) (AXT) assemblage, which appears throughout non-marine (including marginal to freshwater) facies. Fischer et al.(2010) recognized a similar facies association in the coal basinsof Europe. Lebedev (1996) disputed the identity of the Ray-mond Formation assemblage and considered that scales called‘hybodontoid’ by Turner (1993) and the Ageleodus ‘teeth’ wereall specialized denticles belonging (with the associated xenacan-thiform teeth) to an Early Carboniferous xenacanthiform shark.No articulated xenacanth material has been recovered as yet tosupport this hypothesis, although branchial denticles in some ofFritsch’s (1889, 1890) xenacanths do resemble Ageleodus. How-ever, the strong basal growth and histological structure of Ageleo-dus and another of the unusual hand-like teeth, Cynopodius,mitigate against their not being teeth (e.g., Garvey and Turner,2006). Nevertheless, it is possible that most of the scales figured

TABLE 1. Character matrix for selected xenacanthiform and outgroup taxa.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Leonodus 0 0 0 0 1 0 0 2 0 0 0 0 0 ? 0 0 0 ? 0Antarctilamna 1 1 0 0&2 ‘0 0 1 0 2 1&2 0 0 ? 0 0 0 0 0 0Phoebodus 1 3 1 0&1 0&1 0 1 0 0 1&2 2 0 0 ? ? ? ? ? 0Diplodoselache 2 1 1 0&2 1 0 0 2 2 2 0 0 1 0 1 1 0 1 0Hagenoselache 2 2 0 0 1 ? 0 2 1 2 1 1 0 ? ? ? ? ? 1Lebachacacanthus 2 1 2 2 1 ? 0 2 ? 2 1 0 ? 0 1 1 0 1 1Orthacanthus 2 1 2 2 1 0 0 3 1 2 1 0 0 1 1 2 1 1 ?Plicatodus 2 2 0 1 1 0 0 2 1 2 1 1 2 1 2 2 1 1 ?Reginaselache 2 1 0 1 1 0 0 1 0 2 0 0 1 ? 1 1 ? 1 ?Triodus 2 2 0 0 1 1 0 2 0 2 1 1 2 1 2 2 1 1 1Xenacanthus 2 2 1 0&2 1 1 0 2 1 2 0&2 0 0 1 2 2 1 1 ?



FIGURE 12. Lower Carboniferous xenacanthiform sites marked bysolid triangles on an Early Carboniferous (Visean; 340 Ma) paleogeo-graphical reconstruction (after Metcalfe, 1996) with estimated extent ofsouthern glaciation (cf. Jones et al., 2000); Australia: Middle Paddock,Ducabrook Formation in the Drummond Basin, central Queensland;Snowy Plains Formation, Mansfield Group, Victoria; Africa: SekondiFormation, Ghana; Europe: sites in the U.K., mainly Scotland; easternU.S.A. and Canada: sites in New Brunswick and Nova Scotia along north-ern Gondwana margins; see text for stratigraphical and geographicaldetail.

by Turner (1993) might belong to a diplodoselachid shark, whencompared with those illustrated by Dick (1981). Lebedev (1996)had discovered teeth in the D/C boundary beds in Russia, whichhe named ?Diplodoselache antiqua, and these do have smoothcusps more like the type from Scotland than the teeth fromQueensland. Further study of these taxonomic points will be con-sidered elsewhere when further material is available. Interest-ingly, the youngest record for a diplodoselachid has been re-ported from the “Permocarboniferous” lacustrine (lagoonal?)limestone of Guardia Pisano basin, Sardinia (Fischer et al., 2010).

Other isolated teeth from the Mississippian (mid-Visean,Holkerian) Upper St Louis Formation of Heimstra Quarry, nearDelta, Iowa (e.g., Bolt, 1990), resemble those of Orthacanthusin having highly symmetrical smooth cusps with serrated edges(S.T., pers. observ., 1997; Fig. 10E, F), but compare most closelywith those of Dicentrodus bicuspidatus from slightly youngerbeds in Scotland (Hampe, 2003); Hampe et al. (2006) assignedthe American teeth to Dicentrodus sp. 1A, the oldest xenacanthidfound in North America. The only other Mississippian xenacan-thiform is also from Heimstra Quarry (FM collection), whichJohn Bolt (pers. comm. to S.T., 1997) reports as a large, con-siderably flattened specimen with a full set of upper and lowerteeth (not been seen by the authors); an isolated tooth from asample of Upper St Louis Formation bonebed is illustrated here(Fig. 10L, M).

Following the climatic highs of the Devonian (e.g., Younget al., 2010), both marine and non-marine/marginal vertebraterecords in Australia become increasingly sparse throughout theCarboniferous with the onset of the southern glaciation that pre-dominated until later in the Permian (Jones et al., 2000; Fig. 12).Queensland, at least in Visean times, was still in the temperateregion above 60◦ south (Veevers, 2000; Burrow et al., 2010) sothat the Middle Paddock continental to marginal tetrapod andfish fauna, including Reginaselache, was able to flourish. Field-ing et al. (2008:fig. 3) have discerned the oscillating nature of thelong southern glaciation event, and the vertebrate occurrences,including the Ducabrook Formation fauna, support the possibil-ity of later mid-Carboniferous ice age onset in Queensland withmilder interglacial times, with a series of assemblages recordeduntil well into the Pennsylvanian (Burrow et al., 2010).

The last record of a xenacanthiform in the Carboniferous ofthe southeastern Pangaean landmass (eastern Australia) is thatof Reginaselache. The xenacanthiforms presumably then survivedelsewhere (further north in equatorial Paleotethys: see Fig. 12)and only reappear in the stratigraphic record of eastern Australiain the Lazarus taxa of the early to mid-Triassic of the SydneyBasin (Turner et al., 2008).

There exists a note about ‘xenacanthid’ teeth from the LowerCarboniferous Sekondi Formation of Ghana, West Africa (Men-sah, 1973), but absence of specimen data or illustrations does notallow us to gauge this record as truly xenacanthiform. Attempts(by S.T. and O. Hampe, pers. comm., 1999) to obtain materialhave so far proved unsuccessful. Elsewhere in the Lower Car-boniferous of the former western Gondwana, “Xenacanthus” to-cantinsensis (see above) is represented by only a small 30-mm-long spine.

What is the relationship of Reginaselache to younger andbetter-known Carboniferous and Permian taxa from succes-sive lacustrine (and/or possibly marginal lagoonal) horizonsin Stephanian to Asselian basins (see e.g., Werneburg et al.,2007:fig. 9)? Similar Triodus species assigned to Bohemiacanthusby Schneider and Zajıc (1994) include T. carinatus, T. lauteren-sis, T. palatinus, and T. obscurus (Ginter et al., 2010), with thelatter three species showing a stratigraphically older to youngerdecrease in the number of labial and lingual cristae (Schneider,1996:fig. 8). There is still a large temporal gap to fill (see Hampeand Ivanov, 2007:fig. 5) and search of suitable horizons in thesouthern hemisphere should help fill the gaps in the early xe-nacanthiform history, as has already been shown in Queensland,Brazil, and Ghana. Similarly, further work is needed in Pennsyl-vania and maritime Canada, which were part of, or closely asso-ciated with, the northern Gondwanan shore or drainage systemsby the end-Devonian (e.g., Jones et al., 2000; Turner et al., 2005).

Phylogenetically, Hampe (2003) placed xenacanthiforms as thesister group of phoebodontids. Ginter (2004) further discussedthe relationships of Devonian examples of these clades plus Oma-lodontiformes. The teeth found in the Famennian of Red Hill(Fig. 10I) with three median cusplets possibly represent a tran-sitional form related to Antarctilamna within the xenacanthiformlineage (cf. Ginter, 2004:fig. 3). Hampe (2003) did not take intoconsideration the southern hemisphere occurrences of xenacan-thiform teeth. Even if we accept that Leonodus, Antarctilamna(Wellerodus), and such pre-Famennian teeth and spines are notXenacanthiformes s.s., the early incidences of xenacanthiforms inthe Gondwanan regions (Australia, West Africa, Brazil, U.S.A.,and eastern Canada), need to be taken into account (e.g., Turneret al., 2008).

Paleobiology

Comparison with Diplodoselache, Hagenoselache, and Triodussuggests that an adult Reginaselache morrisi was an animal ofaround 1–2 m in length, presumably with smaller juveniles, bear-ing a high tooth complement in each jaw. Based on other LowerCarboniferous xenacanthiforms (e.g., Dick, 1981; Hampe, 2003),the teeth from the type locality, which come from a small areaa few metres square, could be from just one animal or a few in-dividuals (most likely the latter because there are at least threespine tips from the same area), the 1–8 mm size range reflect-ing the growth and tooth-file size range. However, smaller Regi-naselache morrisi teeth in the sample might be from juveniles orsub-adults.

The teeth exhibit a range of color and preservation conditions,which suggests that they were not all fossilized at the same time:some have smoother cusps; some broken cusps, which might haveresulted from the relatively turbulent paleoenvironment and/orburial event; and some have cusps worn down on the tips only.



The latter is surprising considering xenacanth sharks have beenregarded as purely grasping predators; such pathological wearmight represent manipulation of prey or more likely thegosis dur-ing life of the teeth in the tooth files. Johnson and Thayer (2009)did note indications of worn cusps in some of their xenacanthi-form teeth from the Pennsylvanian of Arizona. In addition, othercontemporaneous Early Carboniferous sharks from Scotland,Tristychius (which might also be present in the Narrien Range,cf. Turner, 1993) and Onychoselache, show wear on the toothcusps to such a degree that Dick (1976) surmised a durophagousdiet to produce these strong effects. Our contention, there-fore, is that Reginaselache was not a shark that quickly graspedits prey and swallowed, but one that either might have masti-cated its food to some extent, or experienced opposable wear.The Ducabrook Formation, including beds above and below theTetrapod Unit, preserves evidence of algal mounds that proba-bly formed in standing lagoons; these could have been a possi-ble source of silica-rich food on which Reginaselache might havegrazed occasionally. Another shark in the assemblage, Ageleo-dus, known only from small hand-like teeth (Turner, 1993),might have been an algal nibbler and in turn been prey for thexenacanth.

The spines presumed to be from Reginaselache are compa-rable to those of Diplodoselache (Soler-Gijon, 2000), but thelargest specimen is longer than that of Diplodoselache woodi(see above). The ‘D.’ antiqua spine (Lebedev, 1996:fig. 9g, h)shows similar lateral compression to that of Reginaselache, butthe denticles extend one-third spine length (cf. <1/4 for Regi-naselache). The ridges on Reginaselache are more bark-likeas in D. woodi and not smooth and regular as in ‘D.’ an-tiqua. As in other more primitive xenacanthiforms, the dor-sal spine was presumably positioned in the post-occipital re-gion (Soler-Gijon, 2004). No growth lines (cf. Soler-Gijon andSiebert, 2001) are seen within the ?Reginaselache spine tip(Fig. 6).

Based on the work of Soler-Gijon (2004), the presence ofclosely spaced well-formed denticles on spines indicates that theanimals were post-parturition with erupted spines, possibly fromvery young individuals.

CONCLUSIONS

The mid-Visean xenacanthiform shark Reginaselache morrisi,gen. et sp. nov., from the Ducabrook Formation of centralQueensland, is a new taxon that has teeth morphologically akinto those of Triodus, Bohemiacanthus, Hagenoselache, and Xe-nacanthus found in marine and non-marine beds in the LateCarboniferous to Permian of Europe. The new shark is rep-resented by its numerous ‘diplodont’ teeth, with several asso-ciated spine fragments, a partial lower jaw, and scales highlylikely to be from Reginaselache. Based on a cladistic analy-sis, Reginaselache is placed tentatively within the family Diplo-doselachidae. However, the teeth share few morphological char-acters with the type Diplodoselache woodi and those of anotherpurported but unlikely diplodoselachid, Wurdigneria Richter,2005, although they do resemble other Scottish diplodoselachidtaxa, especially Diplodoselache parvulus. Analysis of teeth andcomparison with those from other Carboniferous sites world-wide shows close morphological similarities with those of thelater Carboniferous–Permian from central Europe. Histologicalstructure is identical to that of the Early Carboniferous Diplo-doselache. The spines of the two taxa are also similar, althoughthat of Reginaselache is comparatively slender.

Where records of older xenacanthiforms occur in the presentSouthern Hemisphere or in terranes that were part of Gondwanaand based on our phylogenetic analysis as well as analysis of asso-ciated fauna, we surmise that the Xenacanthiformes originated inGondwana, inhabiting non-marine/marginal environments. Fur-

ther exploration especially in such deposits across the formernorthern Gondwana is warranted to verify this prediction.

The new Australian xenacanthiform was a shallow-waterdweller within the seaward part of the large Drummond Basinriver system, probably capable of living in marginal and fresh-water environments. Reginaselache morrisi was a medium-sizedpredator well-endowed with a dentition of probably 60 or moresimilarly sized teeth for feeding (possibly even chewing) onsmaller fishes or shelled invertebrates, and predictably, as a basalxenacanthiform, with a post-occipital dorsal fin spine and hete-rocercal tail. Tooth cusp wear suggests a novel style of food pro-cessing for xenacanths.

ACKNOWLEDGMENTS

We are grateful to the Hawkins and Cann families, former andpresent owners of Ducabrook Station, as well as those of neigh-boring stations, for alerting us to the material and allowing access;to C. and J. van der Smissen (Brisbane) for finding and donat-ing the jaw specimen; A. Warren (Melbourne) for preparation;and M. Brazeau (Berlin) for identifying the fragment as shark.S.T. thanks C. Duffin (London), O. Hampe (Berlin), J. Schneider(Freiberg), and G. D. Johnston (Dallas) for discussions and infor-mation on xenacanth teeth; and Hampe for help with histology.E. Daeschler (Philadelphia), S. McLean (Hancock Museum), J.Bolt and W. Simpson (FMNH), and the late C. Patterson (NHM)assisted with and gave permission to use museum collections andspecimens. We are grateful to R. van der Kamp for translations;J. Bracefield, J. Ford, C. Northwood, and K. Stumkat for SEMand research assistance; C. Bonde and B. Tangey for prepara-tion, curation, and databasing of specimens; and to all field workparticipants. Work was initiated when S.T. was ARC AustralianResearch Fellow (1995–2000), financially assisted 1997–1999 and2000–2002 by ARC grants A39700915 and 00000629 to her andA. A. Warren. The Ian Potter Foundation, Melbourne, and theField Museum provided travel grants to S.T. to visit the U.S.A.in 1997. We thank the Queensland Museum Board for basic fa-cilities; QM librarians are ever helpful and Geoscience Australiaalso provided documents. Two referees and editor Dr. CharlieUnderwood provided critical comments for the improvement ofthe manuscript in review.

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Submitted April 30, 2010; accepted October 28, 2010.Handling editor: Charlie Underwood.

APPENDIX 1. Tooth, spine, jaw, and scale characters and char-acter states used in cladistic analysis; comparable characters usedby Hampe (2002), Soler-Gijon (2000), and Heidtke et al. (2004)are noted in brackets.

(1) Number of tooth cusps (Hampe [1], changed polarity): two(0); more than three (1); three (2).

(2) Relative length of lateral versus median cusps (Hampe [2],extra states added): no median cusps (0); median cusp(s)<half height of lateral cusps (1); median cusps shorter but>half height of lateral cusps (2); median and lateral cuspsequal height (3); median cusp higher than lateral cusps(cladodont) (4).

(3) Cusp cutting edges (carinae) (Hampe [3], muricated edgesstate dropped): absent (0); smooth (1); serrated (2).

(4) Cusp cristae (Hampe [5]): cristae straight (0); wavy verti-cally oriented cristae (1); absent (2).

(5) Labial nutrient foramina (Hampe [6]): present (0); absent(1).

(6) Coronal button (new character): separated from cusps (0);close to/contiguous with cusps (1).

(7) Outline of tooth base (Hampe [7], polarity reversed): sub-circular or labiolingually elongate (0); mesiodistally elon-gate (1).

(8) Prominent basal tubercle (Hampe [9]): absent (0); present,horseshoe-shaped (1); present, circular with concavedepression (2); present, circular without depression(3).

(9) Nutrient foramina on basal surface (new character): large, 1or 2 (0); large, >2 (1); small and few (2).

(10) Enameloid layer on teeth (Hampe [12], new ancestral polar-ity state added based on Leonodus): present on upper halfof cusp (0); present on whole cusp (1); absent (2).

(11) Composition of tooth cusps (Hampe [10], polaritychanged): trabecular dentine basal core plus orthodentine(0); orthodentine (1); trabecular dentine (2).

(12) Composition of tooth base (Hampe [11]): trabecular den-tine (0); orthodentine (1).

(13) Composition of coronal button (expanded from Heidtkeet al. [13]): trabecular dentine (0); trabecular dentine domewith orthodentine cap (1); orthodentine (2).

(14) Dorsal spine (Hampe [13]): present, posterior to neurocra-nium (0); present, articulates with neurocranium (1).

(15) Spine cross-section (Hampe [14]): nodose ridged, triangu-lar or laterally compressed (0); circular cross-section, dou-ble row of denticles ventrally (i.e., along trailing edge) (1)dorsoventrally compressed distally, lateral rows of denticles(2).

(16) Spine composition (Hampe [17], Soler-Gijon [9] combined):trabecular dentine with orthodentine outer layer formingridges (0); trabecular dentine, rough surface texture (1); tra-becular dentine, smooth surface texture (2).

(17) Adult spine width/length ratio (Hampe [15]): robust, <1:12(0); slender, >1:12 (1).

(18) Meckel’s cartilage prearticular protuberance (new charac-ter): absent (0); present (1).

(19) Dermal denticles (Hampe [30]): polyodontode (0); mon-odontode (1).

APPENDIX 2. Apomorphy lists for the nodes in the cladogramin Figure 10; Character numbers correspond to those listed inAppendix 1; the double arrow under the Change column rep-resents unambiguous changes and the single arrow → representsambiguous changes; all changes are one step; CI = consistencyindex.

Branch Character Steps CI Change

node 20 → Leonodus 2 1 1.000 1 010 1 1.000 2 0

node 20 → node 12 1 1 1.000 0 → 15 1 1.000 1 → 07 1 1.000 0 18 1 1.000 2 0

node 12 → Antarctilamna 9 1 0.500 0 2node 12 → Phoebodus 2 1 1.000 1 3

3 1 0.500 0 111 1 0.667 0 2

node 20 → node 19 1 1 1.000 0 → 2(Xenacanthiformes) 4 1 0.500 0 → 2

15 1 1.000 0 116 1 1.000 0 → 118 1 1.000 0 → 1

node 19 → node 13 13 1 1.000 0 1(Diplodoselachidae)node 13→ Diplodoselache 3 1 0.500 0 1

9 1 0.500 0 2node 13 → Reginaselache 4 1 0.500 2 1

8 1 1.000 2 1node 19 → node 18 3 1 0.400 0 → 2

9 1 0.500 0 → 111 1 0.667 0 119 1 1.000 0 → 1

node 18 → node 17 14 1 1.000 0 1(Xenacanthidae) 16 1 1.000 1 2

17 1 1.000 0 1node 17 → node 16 2 1 1.000 1 2

3 1 0.400 2 → 04 1 0.500 2 → 0

12 1 0.500 0 115 1 1.000 1 2

node 16 → node 15 13 1 1.000 0 2node 15 → Plicatodus 4 1 0.500 0 1node 15 → node 14 6 1 0.500 0 1node 14 → Triodus 9 1 0.500 1 0node 14 → Xenacanthus 3 1 0.400 0 1

11 1 0.667 1 → 0/212 1 0.500 1 0

node 17 → Orthacanthus 8 1 1.000 2 3


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A Lower Carboniferous Xenacanthiform