[Palaeontology, Vol. 56, Part 2, 2013, pp. 303–343]

A NEW DIVERSE SHARK FAUNA FROM THE WORDIAN (MIDDLE PERMIAN) KHUFF FORMATION IN THE INTERIOR HAUSHI-HUQF AREA, SULTANATE OF OMAN by MARTHA B. KOOT1*, GILLES CUNY2, ANDREA TINTORI3 and RICHARD J. TWITCHETT1 1School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, Devon PL4 8AA, UK; e-mails: [email protected], [email protected] 2Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark; e-mail: [email protected] 3Department of Earth Sciences ‘Ardito Desio’, University of Milan, Via Luigi Mangiagalli 34, 20133, Milan, Italy; e-mail: [email protected] *Corresponding author.

Typescript received 30 December 2011; accepted in revised form 24 July 2012

Abstract: Chondrichthyans are newly reported from the two taxa, Nemacanthus sp. and Amelacanthus cf. sulcatus, autochthonous Wordian Khuff Formation (middle Permian), which have neoselachian affinities and therefore an unclear cropping out in well-exposed, low-palaeolatitude sections in relationship to the recovered teeth. The occurrence of Nem- the interior Haushi-Huqf area of Oman. The shark remains acanthus within this Wordian fauna represents the oldest comprise isolated teeth, dermal denticles and fin spines and record of this taxon and its only known occurrence in the have been recovered by processing limestone in buffered ace- Palaeozoic. Of the remaining genera, Glikmanius has previ- tic acid from bulk rock samples. The fauna consists of ously been recorded from the Wordian, whereas for all the mainly ctenacanthiform and hybodontiform taxa, identified others, this study represents their youngest known strati- as Glikmanius cf. myachkovensis, Glikmanius culmenis sp. graphic occurrence and first occurrence in Guadalupian nov., Omanoselache hendersoni gen. et sp. nov., Omanoselache (middle Permian) strata. This adds significantly to our angiolinii gen. et sp. nov., cf. Omanoselache sp., Reesodus un- knowledge of the global diversity of chondrichthyans preced- derwoodi gen et sp. nov., Teresodus amplexus gen. et sp. nov., ing the end-Guadalupian biotic crisis. Palaeogeographically, Gunnellodus bellistriatus, Khuffia lenis gen. et sp. nov., Khuf- for all taxa, this study represents the first record from the fia prolixa gen. et sp. nov. and Euselachii sp. indet. Addi- western fringe of the marine Neotethyan basin, and only tional specimens include rare teeth of the lonchidiid cf. Cooleyella was previously known from the southern (Gon- ‘Palaeozoic Genus 1’ sp., of the neoselachian Cooleyella cf. dwanan) part of the Pangaean continental margin. fordi and a further indeterminate neoselachian, of an indeter- minate petalodont and of the holocephalan Deltodus aff. mer- Key words: Chondrichthyes, Ctenacanthiformes, Hybodont- curei and Solenodus cf. crenulatus. Fin spines add a further iformes, Neoselachii, Euchondrocephali, Permian.

S harks are predominantly marine top predators, yet origination rates in fish families in the early Triassic. some authors have stated that they were relatively unaf- Twitchett (2001) hypothesized that fluctuations in the fected by the late Permian mass extinction event (Schaeffer quality of the chondrichthyan fossil record are responsible 1973; Patterson and Smith 1987), despite the apparent col- for these disparate views on the evolutionary history of this lapse of their supporting ecosystems. In contrast, Compag- important marine group, with a relatively poor fossil record no (1990) stated that over time chondrichthyan diversity in the middle–late Permian masking the true diversity of has increased and decreased many times, closely following pre-extinction faunas and a much better one in the early diversity fluctuations in other marine and freshwater Triassic enhancing apparent diversity in the immediate organisms, including during the late Permian crisis and the aftermath. Resolution of this debate requires an improved subsequent recovery phase. Benton (1998) also found that understanding of Permian shark faunas worldwide. the late Permian mass extinction had little effect on chon- The geology of the Sultanate of Oman has been of drichthyan diversity and in addition noted particularly high interest to researchers for a number of decades; the first

ª The Palaeontological Association doi: 10.1111/j.1475-4983.2012.01199.x 303 304 PALAEONTOLOGY, VOLUME 56 comprehensive study of the regional geology of the this sequence started along the Neotethyan continental Oman Mountains was made by Glennie et al. (1974). margin following a Wordian transgression that covered This and more recent studies have revealed that there most of Oman (Angiolini et al. 2003a; Richoz et al. are a multitude of localities with Permian–Triassic 2005). It is mainly composed of fossiliferous limestone (P–Tr) outcrops, including boundary sections. The fossil and dolomite (Glennie 2005) and contains the Khuff and chondrichthyans of these localities have, however, barely basal Saiq formations, which unconformably overlie pre- been studied. Preliminary work by Tintori (1998) and Permian basement strata. The Khuff Formation is the Angiolini et al. (2003a) revealed that conodont residues focus of this study and was deposited in a continental from Permian (Guadalupian) limestones of Oman are shelf environment exposed in the Haushi-Huqf area in rich in well-preserved chondrichthyan remains. Schultze the interior of Oman (Fig. 2B–C), whereas the correlative et al. (2008) also reported the presence of xenacanth Saiq Formation formed in a transgressive, shallow-marine sharks in the Artinskian Gharif Formation in the Al environment exposed on the Saiq Plateau in the Jabal al Huqf area of Oman. The aim of the current study is to Akhdar region of the Oman Mountains (Fig. 2B; Glennie provide the first detailed analysis of Permian chondri- 2005). chthyans of Oman through detailed sampling of outcrops from the Haushi-Huqf area and in doing so to improve knowledge of the chondrichthyan fossil record. Khuff Formation This, in conjunction with comparisons to other Wordian faunas, will allow re-assessment of our understanding of Upper Palaeozoic rocks are well exposed on the western the extinction patterns leading up to the late Permian side of the Huqf massif (Angiolini et al. 1998). They event. show two consecutive mega-sequences: the Haushi Group and the Akhdar Group, each recording a major transgressive event (Fig. 1B). The first event was con- GEOLOGICAL SETTING trolled by the last phase of the Gondwanan deglaciation and the second by the opening of the Neotethys (Angio- The Sultanate of Oman is situated on the south-eastern lini et al. 1998). The younger of the two mega-sequences, margin of the Arabian Peninsula. Permian and Triassic the Akhdar Group, comprises the fluvial terrigenous deposits from a gradient of depositional environments are Gharif Formation, which is conformably overlain by the readily exposed throughout the region, which form part marine sandstones, marls and bioclastic limestones of the of the autochthonous Hajar Super-group, the Hawasina Khuff Formation. The base of the Khuff Formation is Allochthonous unit and the Batain Nappes. This study currently placed at the first occurrence of marine bio- focuses on the autochthonous Hajar Super-group clasts in the sandstones (L. Angiolini, pers. comm. (Fig. 1A), which represents a cyclic shallow-marine car- 2011), and the formation contains a rich invertebrate bonate sequence that formed on the Arabian Platform fauna of brachiopods, conodonts, foraminifers, crinoids, (Fig. 2A) between the Guadalupian (mid-Permian) and bryozoans, cephalopods, gastropods, bivalves and ostrac- the late Cretaceous (Richoz et al. 2005). Deposition of ods (Angiolini and Bucher 1999), as well as vertebrate

FIG. 1. A, Correlation of Permian–Triassic autochthonous rock units of Oman (based on Glennie et al. 1974; Glennie 2005). B, Depositional succession of rock units in the Haushi-Huqf area of Oman (based on data from Angiolini et al. 2003a). KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 305

A

B

C

FIG. 2. A, Mollewide plate tectonic map from the Late Permian (260 Ma) illustrating the palaeogeographic position of Oman (modified from Blakey 2009). B, Geological map of Permian–Triassic deposits in Oman, showing sample localities (modified from Glennie 2005). C, Geological map of the Haushi-Huqf area, showing sampled sections from the Khuff Formation (modified from Angiolini et al. 2003a).

remains comprising chondrichthyans, actinopterygians Depositional setting. The Khuff Formation represents a and coelacanths (Angiolini et al. 2003a). A composite log shallow carbonate platform deposited on the outer shelf of the Khuff Formation in the Haushi-Huqf area, based of the Arabian Platform, which faced the spreading Neot- on five sections, was published in Angiolini and Bucher ethys ocean (Angiolini et al. 1998), with a NE–SW ori- (1999), indicating that it reaches a maximum thickness ented coastline (Angiolini et al. 2003a). The Khuff of 30–40 m. Based on that study, and a more recent syn- Formation is currently subdivided into three members. thesis by Angiolini et al. (2003a), an updated summary Member 1 records a rapid regional transgression and the log showing the samples analysed in this study has been onset of carbonate shelf sedimentation and consists of produced (Fig. 3). two units: Unit C is interpreted as a tidal sand flat or 306 PALAEONTOLOGY, VOLUME 56 KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 307 barrier beach in a lagoonal or bay environment, whereas MATERIAL AND METHODS Unit D consists of inner- to outer-shelf sediments from above storm wave base (Angiolini et al. 2003a). Member The material used in this study consists of chondrichth- 2 records outer-shelf conditions below storm wave base yan teeth, dermal denticles and fin spines. The specimens and regular distal tempestites (Angiolini et al. 2003a). were recovered by processing bulk rock samples using Member 3 contains frequent, more proximal bioclastic buffered acetic acid (Jeppsson et al. 1999). The majority tempestites, indicating deposition around storm wave of the material derives from the Wordian Khuff Forma- base, with a siliciclastic influx towards the top indicating tion and was recovered from sections K1 (very near to shallowing towards the lower shoreface (Angiolini and section 5 of Angiolini et al. 1998 starting at 2100¢37¢¢N, Bucher 1999; Angiolini et al. 2003a). Since the study by 5740¢03¢¢E), K3 (exact position unknown), K4 Angiolini and Bucher (1999), the upper boundaries of (2102¢30¢¢N, 5742¢00¢¢E), K5 (exact position unknown) members 2 and 3 have been extended upward, the latter and K7 (2100¢35¢¢N, 5739¢27¢¢E), located in the Haushi to the top of the formation and incorporating a former uplift area, and from a section in the Saiwan area ‘Member 4’ that is no longer distinguished (Angiolini (2051¢43¢¢N, 5736¢10¢¢E). A small amount of material et al. 2003a; L. Angiolini, pers. comm. 2011). derives from a section of the Sakmarian Saiwan Forma- Extremely rich fossiliferous levels are common through- tion in the Jabal Gharif area (1957¢01¢¢N, 5721¢38¢¢E). A out the formation, but particularly frequent in Member 1 multitude of small samples (3–5 kg) were collected by and the lower part of Member 3 (Angiolini et al. 2003a). one of the authors (AT) and Prof. L. Angiolini, and in The brachiopod fauna contains Tethyan genera, indicating addition, four bulk rock samples were collected by AT for a warm, subtropical climate (Angiolini et al. 1998), as well vertebrate purposes and comprise 10–15 kg samples from as endemic, Gondwanan and cosmopolitan genera (Angio- four bioclastic limestone beds, all of which were processed lini and Bucher 1999), suggesting that the depositional set- at the University of Milan. Some of their material was ting of the Khuff Formation was open to outside influence. reported as part of the vertebrate fauna found by Angio- The conodont association confirms the shallow marine set- lini et al. (2003a) through their detailed sampling of the ting (Angiolini et al. 2003a). Fish remains have been Khuff Formation, but was not figured or described in recovered throughout the formation, mostly from shallow- detail. The samples, for which the stratigraphic position water shell beds (Angiolini et al. 2003a) redeposited as was recorded (thus excluding 27 shark-containing sam- storm layers. ples), have been indicated on the composite log (Fig. 3). Of the four large samples, AO40 from K1 represents Age. An upper Wordian age (Guadalupian, Permian) has the upper part of a storm layer very rich in brachiopods been assigned to the Khuff Formation, based on brachio- shells, whereas AO55, AO47bis and AO50 were taken pod and conodont faunas (Angiolini et al. 1998). The fauna from K4, a section that consists in the lower part of bio- in Member 1 is interpreted as Wordian, based on Roadian– clastic calcarenite and calcirudite (storm concentration of Wordian brachiopods and Wordian–Capitanian conodonts allochthonous fossils), interbedded with marly limestone, (Angiolini et al. 2003a, but also see Shen et al. 2009 and and in the upper part of shell beds from more proximal Mei and Henderson 2001, respectively). Higher in the suc- settings (L. Angiolini, pers. comm. 2011). Over 2100 cession, some brachiopod differentiation occurs whereas specimens were recovered from the four large samples the conodont assemblage remains unaltered, but a Wordian alone, enabling a detailed reconstruction of the composi- age is still valid for Member 2 and Member 3 (Angiolini tion of the Wordian shark community in the Haushi- et al. 2003a). The Khuff Formation can be biostratigraphi- Huqf region. Specimens from the smaller samples have cally correlated to the lower part of the Saiq Formation, only been used in the systematic part of this study if they cropping out in the Oman Mountains (Angiolini et al. represent taxa that do not occur in the large samples. For 2003a; Koehrer et al. 2010), and to formations further the remainder of the study, they have been used to com- afield, such as the Amb Formation of the Salt Range in plete the range data for the most common taxa. Pakistan and the Rat Buri Limestone of South Thailand Additional material was sampled in the Haushi Cliff (Mei and Henderson 2001; Angiolini et al. 2003a). area and at two sections in the Saiwan area: 6–2 at

FIG. 3. Stratigraphy (summary composite log), sample heights and chondrichthyan occurrence data (MPUM collection) for the Khuff Formation in the Haushi-Huqf area, modified from Angiolini and Bucher (1999) to reflect changes in member boundaries, as well as a typical deposit of the Saiwan Formation from Jabal Gharif, based on data in Angiolini et al. (2003b). Conodont biozonation and Sakmarian ammonoid and fusulinid biozonation from Henderson (2005); Wordian palynological standard OSPZ Arabian biozonation from Jan et al. (2009); Wordian Tethyan fusulinid biozonation from Kotlyar and Pronina (1995) as assigned by Angiolini et al. (1998). Black indicates correlation of samples to exact bed, grey indicates approximate position. 308 PALAEONTOLOGY, VOLUME 56

2052¢26¢¢N, 5735¢15¢¢E; 6–3 at 2052¢38¢¢N, 5734¢60¢¢E SYSTEMATIC PALAEONTOLOGY and 6–7 at 2100¢37¢¢N, 5739¢36¢¢E (C. M. Henderson, pers. comm. 2010). The samples were collected by Prof. Class CHONDRICHTHYES Huxley, 1880 C. M. Henderson from the University of Calgary, Alberta, Subclass ELASMOBRANCHII Bonaparte, 1838 Canada, and were initially intended for conodont Superorder CLADODONTOMORPHI Ginter, Hampe and research. Each sample is estimated to have been a maxi- Duffin, 2010 mum of 5 kg. The samples were collected from gently Order CTENACANTHIFORMES Glikman, 1964 dipping beds along sub-horizontal sections, each within a Family CTENACANTHIDAE Dean, 1909 different wadi, and their stratigraphic position was recorded as a horizontal distance from the base of the Genus GLIKMANIUS Ginter, Ivanov and Lebedev, 2005 formation (A. Baud, pers. comm. 2011, 2012; Fig. 4). Due to the absence of more detailed stratigraphic data or dip Type species. Cladodus occidentalis Leidy, 1859; from the Penn- measurements, precise correlation with sections K1 and sylvanian upper Coal Measures of Manhattan, Kansas, USA. K4 is not possible (A. Baud, pers. comm. 2011). The for- mation is not very thick, however, and based on a general Diagnosis. Sharks with cladodont teeth having a robust, uniformity in the conodont and vertebrate assemblages triangular median cusp, strongly convex lingually and (Angiolini et al. 2003a), the material is assumed to be slightly convex or flattened labially, with a shallow to closely time-equivalent. well-developed depression in the basolabial part. There The chondrichthyan systematics is based on the most are usually one to four pairs of lateral cusps, the outer- recent work available, namely Ginter et al. (2010) for Pal- most the largest. At least one pair of intermediate cusplets aeozoic elasmobranchs. In some cases, other publications is not in line with the others, but positioned labially. The are followed, because a consensus has not yet been base is reniform, with two compact basolabial projections reached on many aspects of chondrichthyan systematics. flanking the labial depression and two widely spaced but- The use of open nomenclature is based on the recom- tons on the oral–lingual side (emended from Ginter, Iva- mendations of Bengtson (1988). nov and Lebedev 2005).

Repository. All specimens from the samples collected by AT and Remarks. The ctenacanthiform relationship of this mate- Prof. L. Angiolini are deposited in the Palaeontological Museum rial is evidenced by the presence of the cladodont tooth of the University of Milan (MPUM10880–MPUM10953 and morphology with a flattened labial face of the main cusp MPUM11002–MPUM11058; see Supporting Information Appen- and a well-developed basolabial indentation. Similarities to dix S1). symmoriiform teeth exist, because they are also of the All specimens from the samples collected by Prof. C.M. Hen- cladodont type, but significant differences are that the derson are deposited in the palaeontological collection at the main cusp is not biconvex (the sole exception is the labi- University of Calgary (UC20231–UC20385; see Supporting Infor- mation Appendix S2). ally flattened main cusp in Symmorium reniforme Cope, 1893) and that there are two basolabial projections and Institutional abbreviations. UC, University of Calgary, Calgary, orolingual buttons, as opposed to single ones (Ginter et al. AB, Canada; MPUM, Palaeontological Museum of the University 2010). The referral of this material to Glikmanius is based of Milan, Milan, Italy. on the presence of a deep basolabial indentation, framed by two projections and two orolingual buttons, which are characteristics of this genus (Ginter et al. 2005). The genus was tentatively assigned to the Ctenacanthidae by Ginter et al. (2010), based on spine morphology, which is not affected by the emendation of the diagnosis here.

Glikmanius cf. myachkovensis (Lebedev, 2001) Figure 5A–H

2001 Symmorium? myachkovensis Lebedev, pp. 196–197, pl. 41, fig. 4. 2005 Glikmanius myachkovensis Ginter, Ivanov and Lebedev, pp. 627–629, figs 2C, 3A–F.

FIG. 4. Stratigraphic position of samples from Haushi Cliff Material. Samples AO40, AO55, AO47bis, AO50, Khuff Forma- and Saiwan (UC collection) per sample location. tion, yielded 649 specimens of variable completeness and with KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 309 some indications of wear. Specimens used for SEM imaging: are also observed in the material described here, include MPUM10926, MPUM10927; remaining specimens: MPUM10893 buttons that are generally positioned somewhat away (65), MPUM10914 (420), MPUM10933 (54), MPUM10946 (108). from the lingual basal margin and the lingualmost part of the base sloping downward. The intermediate cusplets are Description. Teeth are large, of robust appearance and symmetrical out of alignment with the median and outermost cusps (generally 4 mm mesio-distally, 2.5 mm labio-lingually and and substantially displaced labially, but still more linearly 3.5 mm high). Tooth fragments indicate that smaller and larger arranged than in G. occidentalis. Nevertheless, there are teeth (up to twice the size) may occur. The crown is composed of a main cusp and two pairs of lateral cusplets with a coarse ornamen- some differences between this material and G. myachkov- tation pattern. The main cusp has almost parallel cutting edges, is ensis. The most significant is the very low heterodonty in distinctly convex on the lingual side and more flattened to basally this material. The presence of two lateral cusplet pairs is concave on the labial side. Both pairs of lateral cusplets are less consistent and independent of the size of the teeth, in than half the height of the main cusp and fan out to a maximum of contrast to the usually larger number of intermediate cus- 30 degrees from the vertical main cusp. The outer pair of cusplets plets (3–4) in typical G. myachkovensis teeth of this size is slightly higher and more robust than the intermediate pair. All (2–4 mm) and the occasionally unequal number of lateral cusps are projected labially but curve lingually and are also not cusplets. A ridge connecting the two orolingual buttons is aligned mesio-distally. The main cusp is positioned lingually, and also sometimes suggested in the material, but not gener- the intermediate cusplet pair more labially, relative to the outer ally present. Lastly, the ornamentation pattern is variable cusplet pair. The cutting edges are positioned labially on the cusps. and often less dense than in G. myachkovensis. These dif- The ornamentation pattern is variable, which may be influenced by wear. The most pronounced ornamentation is a pair of vertical ferences are deemed insufficient to warrant full separation cristae running almost parallel along the labial side of each cusp of this material, which is why it is listed as G. cf. myach- and converging near the apex and a pair of cristae close to the cut- kovensis. It would represent the only Permian record of ting edges on the lingual face. If preserved, the density of ornamen- the species, which was previously only known from the tation is somewhat greater with 6–8 acute cristae on both lingual Pennsylvanian (Carboniferous; Ginter et al. 2005, 2010). and labial faces of the cusps. The cristae on the labial face of the main cusp generally follow the narrowing edges, but a specific sculpture is only present on larger specimens and involves a slight Glikmanius culmenis sp. nov. turning out of the cristae, after which they become vertical and Figure 5I–T turn back inward to follow the edges until they fade near the apex. The base is low and trapezoidal in apical outline with rounded Derivation of name. Derived from the Latin culmen ‘peak’. angles and a central basolabial depression (continued in the main cusp). Two well-separated, circular and rounded buttons Holotype. One complete tooth (MPUM10928, Fig. 5Q–T). are present on the oral side of the lingual torus, which can be unequal in size and if so, the larger causes an asymmetry in the lingual root face. Two pronounced basolabial projections with Paratypes. Two complete teeth (MPUM10909, Fig. 5I–L; an almost flat basal surface occur on either side of the basolabial MPUM10910, Fig. 5M–P). depression. The basal face is generally concave and shows a small central lingual sulcus. The lingualmost part of the base beyond Type locality. Haushi Cliff, Haushi-Huqf area, central eastern the orolingual buttons is directed downward. Numerous small Oman. and randomly located foramina occur on both the basal and oral sides, which may become more obvious as the result of wear, Type stratum. Bioclastic limestone bed at 25 m height on com- but 2–4 larger foramina obliquely penetrate the full depth of the posite log of Angiolini and Bucher (1999), sampled at section base in between the two orolingual buttons. K4, Khuff Formation, Akhdar Group, Wordian (Guadalupian, middle Permian). Remarks. This material is attributed tentatively to G. my- achkovensis (Lebedev, 2001) rather than to the other Material. Samples AO40, AO55, AO47bis, AO50, Khuff Forma- named species of the genus, G. occidentalis (Leidy, 1859, tion, yielded 137 specimens of variable completeness and with some indications of wear. Specimens used for SEM imaging: sensu Ginter et al. 2005). This is firstly based on the small MPUM10909, MPUM10910, MPUM10928; remaining speci- size of the teeth, because G. myachkovensis is typically 2– mens: MPUM10894 (25), MPUM10915 (101), MPUM10934 (3), 4 mm in size and significantly smaller than typical G. oc- MPUM10947 (5). cidentalis (mm vs. cm scale). Secondly, the main cusp is long and slender, matching the typical description of Diagnosis. Cladodont teeth with lingually curved biconvex G. myachkovensis, which is also true for the weak develop- main cusp and up to two small cusplet pairs. Outermost ment of the basolabial depression and projections and the cusplet pair larger and innermost pair offset labially. orolingual buttons, in comparison with G. occidentalis. Rarely, a third incipient cusplet pair flanks the main cusp. Further typical characteristics of G. myachkovensis, which Fine ornamentation pattern consisting of anastomosing 310 PALAEONTOLOGY, VOLUME 56

B D

C A

E H F

G

L

I J

K

P M

N

O

Q T R

S KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 311 vertical cristae. Trapezoidal base with lingual apron. Weak Whether they are rounded or ridge-like is difficult to determine development of two well-separated orolingual buttons. due to their weak development, but general observations seem Slight basolabial depression. Vascularization consisting of to be inclined towards the latter, which may indicate a centrally numerous randomly located small foramina and one large depressed shelf. This hypothesis seems to be corroborated by a foramen obliquely penetrating the entire depth of the base remotely shelf-like appearance without a central depression that was observed in one instance. The basal face also shows a wide in the central part. and shallow mesio-distal furrow. Numerous randomly located small foramina occur on the orolabial and basal face of the base, Description. Cladodont teeth of variable size (generally measur- which may again be made more obvious as the result of wear. ing 2–3 mm mesio-distally, 1–1.5 mm labio-lingually and One (rarely two) large foramen opens centrally on the lingual 2–3 mm high, but the largest recorded dimensions are 8 mm edge and obliquely penetrates the full depth of the base. mesio-distally, 5 mm labio-lingually and 8 mm high). The crown consists of a high biconvex main cusp with somewhat flattened Remarks. The cladodont morphology of these teeth, indi- labial face and up to three lateral cusplet pairs, which are very small in comparison with the main cusp and point away from cated by the high and slender main cusp flanked by smal- it. They may also be entirely lacking. The third (innermost) cus- ler lateral cusplets of which the outermost pair is the plet pair is incipient and only rarely present. In case of two cus- larger, as well as the shallow base projecting lingually, plet pairs, the outermost is the larger and in apical view, the warrants inclusion of the material within the Cladodonto- innermost is not in line with the other cusps, but offset labially. morphi. However, whether the species is closer to the The main cusp is distinctly curved lingually and bears very faint Ctenacanthiformes or the Symmoriiformes can be argued cutting edges (best defined near the base). The ornamentation based on a number of key morphological characteristics, pattern extends across all cusps and consists of fine cristae that the interpretation of which points in different directions. run vertically. They are most numerous at the base and reduce First of all, the biconvex nature of the main cusp with an in number due to anastomosing on the bottom half of the cusp. only slightly flattened labial face suggests a symmoriiform They extend along the full length of the cusps and only fade affinity (Ginter et al. 2010), whereas the variable degree close to the apex. Wear can cause the entire labial face to be smooth, and cristae only remain lingually near the base, being of the basolabial depression leaves any interpretation faintest in the central part. It may also be responsible for diffi- inconclusive. Any resemblance to a shelf-like structure is culty in observing a histological connection between the cusps suggestive of either symmoriiforms or ctenacanthids. The by means of an enameloid or pallial dentine layer. Its existence consistent presence, and sometimes stronger, development can be seen in the best preserved specimens, although its extent of the basolabial depression, nevertheless, suggests a cten- is limited. The oral surface of the base appears to be largely acanthid relationship, for which a shallow depression is a devoid of hypermineralized tissue, but the enameloid is contin- typical familiar characteristic, as opposed to its frequent ued in between the cusps on the apico-labial margin and may absence in symmoriiforms (Ginter et al. 2010). This is also expand onto the labial face. Some of the cristae (especially supported by the correlative development of two separate the cutting edges) from adjacent cusps appear to join up. basolabial projections, which is a diagnostic feature of the The base is approximately trapezoidal in apical outline, but ctenacanthid genus Glikmanius Ginter, Ivanov and Lebe- may appear very rounded or restricted in extent, which is most likely also due to wear or abrasion. The base is low, and the dev, 2005, as is the presence of two well-separated orolin- cusps are positioned on the labial edge, creating a lingual apron. gual buttons, rather than the single oval button or labio- The apron bears two well-separated orolingual buttons, which lingual groove typical for the Symmoriiformes (Ginter are weakly developed and are often merely a rise in the orolin- et al. 2005, 2010). Most importantly, the likelihood of a gual surface of the base. Normally following the degree of devel- ctenacanth relationship is suggested by a histological con- opment of the buttons, a shallow central depression occurs nection between the cusps, even if limited, by means of labially, which is generally restricted to the base of the main an enameloid or pallial dentine layer, which is lacking in cusp and the labial basal face (the basolabial margin appears symmoriiform taxa (Ginter et al. 2010). Overall, it is straight in labial view), but may be continued onto the basal face considered that some transitional characteristics may be (causing the basolabial margin to appear indented underneath present, but that the presence of a histological connection the main cusp in labial view). In the case of a continued basola- between cusps most reliably indicates a closest affinity bial depression, two slight basolabial projections occur directly on either side that are restricted in their mesio-distal length. with the Ctenacanthiformes. In comparing descriptions of

FIG. 5. Ctenacanth teeth from the Khuff Formation, Haushi Cliff, Haushi-Huqf area, central eastern Oman. A–H, Glikmanius cf. myachkovensis (Lebedev, 2001). A–D, MPUM10926, loc K4, sample AO47bis; tooth. A, lingual, B, labial, C, apical, and D, lateral views. E–H, MPUM10927, loc K4, sample AO47bis; tooth. E, lingual, F, labial, G, apical, and H, lateral views. I–T, Glikmanius culmenis sp. nov. I–L, MPUM10909, loc K4, sample AO55; tooth, paratype. I, lingual, J, labial, K, apical, and L, lateral views. M–P, MPUM10910, loc K4, sample AO55; tooth, paratype. M, lingual, N, labial, O, apical, and P, lateral views. Q–T, MPUM10928, loc K4, sample AO47bis; tooth, holotype. Q, lingual, R, labial, S, apical, and T, lateral views. All scale bars represent 500 lm. 312 PALAEONTOLOGY, VOLUME 56 ctenacanthid genera in Ginter et al. (2005, 2010) with the the crown and is almost never recovered with the crown. material described here, strong similarities in crown mor- This latter phenomenon has, however, not been men- phology with Ctenacanthus become obvious and in partic- tioned before in literature. In addition to this, the base in ular with Ctenacanthus concinnus, as well as some the material here is observed to possess more right angles similarities with Cladodus bellifer, which is said to possess and larger foramina than in Mesozoic hybodont teeth, a mixture of features of Cladodus s.s. and Glikmanius oc- but this may fall within the expected variation among cidentalis (Ginter et al. 2010). Heslerodus possesses similar taxa within the order. basal characteristics to Glikmanius (Ginter et al. 2005, 2010), but is disregarded based on significant differences with its phoebodont-like crown. The fact that Glikmanius Family INCERTAE SEDIS typically possesses a moderate to deep basolabial depres- sion (Ginter et al. 2010) could be used in argument Genus OMANOSELACHE gen. nov. against the inclusion of culmenis, but it is considered that Derivation of name. Derived from ‘Oman’, the country of origin, the weak expression of the orolingual buttons and basola- and from the Greek selakhos ‘shark’. bial projections is continued in the basolabial depression. The well-separated nature of the two orolingual buttons Type species. Omanoselache hendersoni gen. et sp. nov.; from the and basolabial projections is deemed to adequately distin- Wordian (Guadalupian) Khuff Formation of the Haushi-Huqf guish the material from any other genera with which it area, central eastern Oman. may share crown characteristics and therefore support its assignment to Glikmanius. Diagnosis. Gradual monognathic heterodont dentition consisting of elongate teeth, which are basally arched and symmetrical anteriorly and asymmetrical (antero)laterally. Cohort EUSELACHII Hay, 1902 Moderate main cusp with rounded apex. Up to two pairs Order HYBODONTIFORMES Maisey, 1975 of lateral cusplets may be present with two additional cusplets on the distal extremity in asymmetrical teeth. Remarks. The material described in this study displays Longitudinal crest always present, sometimes with crenu- characteristics typical for hybodont crown morphology, lations. Strong lingual peg with pronounced surmounting including a prominent main cusp that is always higher vertical crista. Small labial peg, often indented. Crown than the lateral cusplets, with cusplet height decreasing surface smooth or with a small number of cristae. Base away from the centre of the tooth, and a very gradual with lingual protrusion. Anaulacorhize vascularization heterodonty pattern (Ginter et al. 2010). However, the with randomly located foramina, which may be enlarged base morphology is unusual compared with typical hy- lingually. Labially, a row of small foramina occurs near bodonts known from the Mesozoic. ‘Palaeozoic small- the crown–base junction in addition to larger foramina toothed hybodonts are extremely poorly known’ (Rees opening in the basolabial sulcus. and Underwood 2002, p. 471), and in particular the base structure, which is due to a lack of isolated teeth and Distribution. Central eastern Oman. poor visibility in preserved body fossils. The material from the Khuff Formation provides an exceptional oppor- Stratigraphical range. Wordian, Guadalupian, middle Permian. tunity for comparison due to the abundance of isolated teeth preserved with the base still attached to the crown Omanoselache hendersoni sp. nov. in virtually every instant. This in itself is a noteworthy Figure 6A–L feature of Palaeozoic hybodont teeth, substantiated by fig- ured material in previous publications (Johnson 1981), Derivation of name. Named after Charles Henderson (University because it is a widely recognized characteristic of Meso- of Calgary) in recognition of his kindness shown by making zoic hybodonts that the base has a weak attachment to material from his personal collection available for study.

FIG. 6. Hybodont teeth from the Khuff Formation, Haushi Cliff, Haushi-Huqf area, central eastern Oman. A–L, Omanoselache hendersoni gen. et sp. nov. A–D, MPUM10883, loc K1, sample AO40; tooth, paratype. A, lingual, B, labial, C, apical, and D, lateral views. E–H, MPUM10884, loc K1, sample AO40; tooth, holotype. E, lingual, F, labial, G, apical, and H, lateral views. I–L, MPUM10885, loc K1, sample AO40; tooth, paratype. I, lingual, J, labial, K, apical, and L, lateral views. M–X, Omanoselache angiolinii gen. et sp. nov. M–P, MPUM10929, loc K4, sample AO47bis; tooth, paratype. M, lingual, N, labial, O, apical, and P, lateral views. Q– T, MPUM10887, loc K1, sample AO40; tooth, holotype. Q, lingual, R, labial, S, apical, and T, lateral views. U–X, MPUM10930, loc K4, sample AO47bis; tooth, paratype. U, lingual, V, labial, W, apical, and X, lateral views. Y–AB, cf. Omanoselache sp. MPUM10886, loc K1, sample AO40; tooth. Y, lingual, Z, labial, AA, apical, and AB, lateral views. All scale bars represent 300 lm. KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 313

A

B

C

D

E

F G

H

I

J K

L

N

O

M P

Q

R

S

T U

V W

X

Y

Z

AA

AB 314 PALAEONTOLOGY, VOLUME 56

Holotype. One complete tooth (MPUM10884, Fig. 6E–H). ber of additional cristae on the lingual face of the main cusp, a raised longitudinal crest that is crenulated to near-cusped and a Paratypes. Two complete teeth (MPUM10883, Fig. 6A–D; crown shoulder that displays crenulation or small nodes with MPUM10885, Fig. 6I–L). associated vertical cristae that may be worn labially. The base is straight to concave in outline labially and convex Type locality. Haushi Cliff, Haushi-Huqf area, central eastern lingually, causing a lingual protrusion of the base. A basolabial Oman. sulcus extends mesio-distally across the entire tooth. The lingual face of the base displays randomly located foramina of varying Type stratum. Bioclastic limestone bed at 16 m height on com- sizes that approach a row-like arrangement. In anterior teeth, posite log of Angiolini and Bucher (1999), sampled at section the foramina are enlarged to correspond with the height of the K1, Khuff Formation, Akhdar Group, Wordian (Guadalupian, base. Labially, foramina are present in two rows, one consisting middle Permian). of small foramina near the crown–base junction and one consist- ing of larger foramina opening basolabially at the upper edge of Material. Samples AO40, AO55, AO47bis, Khuff Formation, the sulcus. The vascularization type is anaulacorhize. yielded 717 complete and broken specimens. Specimens used for SEM imaging: MPUM10883 (anterior), MPUM10884 (anterolat- Remarks. With the lingual and labial pegs at roughly the eral), MPUM10885 (lateral); remaining specimens: MPUM10896 same height, the indentation in the labial peg is likely (576), MPUM10917 (104), MPUM10936 (34). indicative of an interlocking tooth arrangement with the lingual peg articulating in the indentation. The presence Diagnosis. Crown surface smooth and lateral cusplets of anaulacorhize vascularization type and gradual mono- absent. Anaulacorhize vascularization with randomly gnathic heterodonty imply a hybodontiform relationship. located foramina, lingually enlarged in anterior teeth. Ba- Moreover, acid etching of fractured teeth revealed a single solabial sulcus always present. crystallite enameloid with pillar-like bundling similar to the microstructure of the teeth of Triassic hybodonts Description. The teeth are elongate, of variable size (smaller described by Cuny et al. (2001). The low crown morphol- specimens are 1.0–1.2 mm mesio-distally, 0.6–0.9 mm labio-lin- ogy can be accommodated by the varied tooth morpho- gually, 0.6–0.8 mm high; specimens up to twice the length are logies included in the Hybodontoidea, and mild common and teeth measuring 3–4 mm mesio-distally also occur heterodonty is common within the order Hybodontifor- frequently) and of varying degrees of symmetry, indicating the mes (Ginter et al. 2010). The heterodonty pattern resem- presence of gradient monognathic heterodonty. The anterior bles that present in the Acrodontinae, described (as teeth are nearly symmetrical and have a robust appearance with the crown being up to twice the height of the base in the central Acrodontidae Casier, 1959) in Ginter et al. (2010), but a part and only attaining more equal height laterally. The base is close relationship with the Acrodontinae is excluded moderately arched, causing the extremities to fall away from the based on the differences in ornamentation pattern, the main cusp to the extent that the distalmost part is situated presence of a lingual and labial peg and a less porous below the height of the lingual peg, which, together with the base. Omanoselache may be representative of a separate, near symmetry of the teeth and massive main cusp, creates an short-lived family, but due to a poor understanding of overall triangular shape. The anterolateral teeth are distinctly Permian Hybodontiformes, this genus is left without fam- asymmetrical with strong arching of the base underneath the ily assignment. Some similarities in crown morphology main cusp. The distalmost part of the unequal extremities there- with ‘Polyacrodus’ lapalomensis Johnson, 1981, are noted, fore reaches far below the height of the lingual peg. The lateral but the lack of any basal arching precludes assignment to teeth display a gradient of slight to strong asymmetry, and the this species. basal arching is moderate to nearly absent, which means that their extremities are merely sub-horizontal or slightly declined and that their distalmost part is positioned around the same height of the lingual peg. In all teeth, unrelated to tooth posi- Omanoselache angiolinii sp. nov. tion, the main cusp is low to moderately high, with a rounded Figure 6M–X apex. Lateral cusplets are absent. A longitudinal crest is always present, which is generally low and rounded but may be more Derivation of name. Named after Lucia Angiolini (University of acute and slightly crenulated. The lingual peg is strong and has a Milan) in recognition of her kindness shown by making material pronounced surmounting crista connecting it to the apex of the available for study and providing invaluable information on its main cusp. The labial peg is small and rounded, but is also often stratigraphical context. indented. The crown–base junction is moderately incised. The crown surface is generally smooth, but a few short, coarse cristae Holotype. One complete tooth (MPUM10887, Fig. 6Q–T). may additionally appear radiating from the apex of the main cusp, and the basal part of the crown may be crenulated labially Paratypes. Two complete teeth (MPUM10929, Fig. 6M–P; and lingually at the height of the crown shoulder. A number of MPUM10930, Fig. 6U–X). teeth display a more distinct ornamentation with a varying num- KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 315

Type locality. Haushi Cliff, Haushi-Huqf area, central eastern foramina opening basolabially at the upper edge of the sulcus. Oman. The vascularization type is anaulacorhize.

Type stratum. Bioclastic limestone bed at 16 m height on com- Remarks. The basal morphology of this material is identi- posite log of Angiolini and Bucher (1999), sampled at section cal to that of O. hendersoni sp. nov., and the heterodonty K1, Khuff Formation, Akhdar Group, Wordian (Guadalupian, pattern and crown features are similar. This material is middle Permian). differentiated from O. hendersoni and established as a spe- cies in its own right because all the tooth types that com- Material. Samples AO40, AO55, AO47bis, AO50, Khuff Forma- pose the heterodont dentition possess a cuspidate crown. tion, yielded 86 complete and broken specimens. Specimens used Other differences include the much less massive anterior for SEM imaging: MPUM10929 (anterior), MPUM10887 (ante- rolateral), MPUM10930 (lateral); remaining specimens: teeth and the development of a slight rim at the crown MPUM10898 (34), MPUM10919 (25), MPUM10938 (19), shoulder. The possibility of sexual dimorphism (gynan- MPUM10949 (5). dric heterodonty) to account for the presence of lateral cusplets (with O. hendersoni representing the female and Diagnosis. Moderate main cusp with blunt apex and cus- O. angiolinii the male) is discounted, because it is pidate crown. Lingual peg positioned low. Smooth crown, assumed that only the anterior teeth, the ones actually sometimes with small number of cristae radiating from involved in copulation, would be cuspidate in that case. cusp apices reaching down to crenulated crown shoulder. The material bears resemblance to ‘Polyacrodus’ wichitaen- Anaulacorhize vascularization with some enlarged foram- sis Johnson, 1981, with regard to a number of characteris- ina lingually. tics in both the crown and base, but cannot be attributed to it because of the absence of the lingual peg and the Description. The teeth are elongate (1.6–1.9 mm mesio-distally, occurrence of lateral cusplets exclusively on the distal 0.5 mm labio-lingually, 0.6–0.7 mm high) and show gradient extremity in ‘P.’ wichitaensis. The most ornamented teeth monognathic heterodonty. This is most clearly expressed in the in O. angiolinii appear to be smaller, which is consistent degree of asymmetry and the arching of the teeth. Anterior teeth with the general pattern of clutching dentitions occurring approach symmetry and are slightly arched in the base to mod- in juveniles and more crushing dentitions in adult speci- erately in the crown. Anterolateral teeth are distinctly asymmet- mens. rical with strong arching at the position of the main cusp, causing the extremities to drop below the level of the lingual and labial peg in the distalmost part. The lateral teeth show a strongly varying degree of asymmetry and are moderately arched cf. Omanoselache sp. to near-straight. The main cusp remains low and is rounded in Figure 6Y–AB lateral teeth, but is up to twice the height of the rest of the crown in the anterolateral and anterior teeth and becomes Material. Samples AO40, AO55, AO47bis, Khuff Formation, bluntly pointed. It may also be slightly distally slanted. Two yielded 14 complete and broken specimens. Specimen used for pairs of lateral cusplets are present in near-symmetrical teeth, SEM imaging: MPUM10886; remaining specimens: MPUM10897 and in the case of strong asymmetry, two cusplets are present (4), MPUM10918 (4), MPUM10937 (5). mesially and up to four cusplets distally. A longitudinal crest is always present, which is acute. The lingual peg is strong and Description. The teeth are very robust and have a flattened robust, positioned low and has a surmounting vertical crista appearance. They are elongate (2.5 mm mesio-distally, 1 mm connecting it to the apex of the main cusp. A small labial peg is labio-lingually, 0.9 mm high) and slightly but clearly asymmetri- present and may be indented, but is much weaker developed in cal. The crown is very much flattened due to a low main cusp lateral teeth. The crown is smooth, but a small number of addi- and generally smooth. Lateral cusplets are absent. A longitudinal tional straight to slightly wavy cristae may appear on the main crest is present but remains low. The lingual peg is strong and and lateral cusps lingually and labially, generally radiating from situated very low, whereas the labial peg is small and may be their apices. The development of these cristae is accompanied by indented. Somewhat more ornamented teeth do occur, which the slight crenulation of the otherwise smooth crown shoulder, display a crenulated crown shoulder and vertical cristae lingually which is often slightly raised to form a longitudinal rim, but can and labially. develop into small nodes at the position of the cusplets. This is The lingual basal edge is straight, but labially it is slightly con- most pronounced lingually. cave following from the presence of a basolabial sulcus extending The base is straight to concave in labial outline and convex in mesio-distally across the entire tooth. An extreme lingual protru- lingual outline, which creates a lingual protrusion of the base. A sion of the base adds to the flat appearance of the teeth. The lin- mesio-distally wide basolabial sulcus is present. The lingual face gual face of the base displays enlarged and randomly located of the base displays randomly located or sometimes row-like foramina. Labially, foramina are present in two rows, one con- foramina of varying sizes, since some may be enlarged. Labially, sisting of small foramina near the crown–base junction and one foramina are present in two rows, one consisting of small foram- consisting of larger foramina opening basolabially at the upper ina near the crown–base junction and one consisting of larger edge of the sulcus. The vascularization type is anaulacorhize. 316 PALAEONTOLOGY, VOLUME 56

Remarks. The morphology of this material is generally rem- Rees and Underwood (2002) in principle, although they iniscent of Omanoselache hendersoni gen. et sp. nov. but the have continued to accommodate the material in Lissodus as teeth are slightly larger, not arched, restricted in height and part of the Lonchidiidae for ease of reference. more robust. The quantity of the material is limited, how- ever, and it does not display a heterodonty pattern. It is Distribution. Derbyshire, southern England, western and central considered closely affiliated to Omanoselache gen. nov. Russia, central eastern Oman.

Stratigraphical range. Tournaisian, Mississippian, early Carbonif- Genus REESODUS gen. nov. erous–Wordian, Guadalupian, middle Permian.

Derivation of name. Named after Jan Rees (Karlstad University, Sweden) in recognition of his important work on the taxonomy Reesodus underwoodi sp. nov. of the genus Lissodus and the ancient Greek odous ‘tooth’. Figure 7A–D

Type species. Reesodus underwoodi gen. et sp. nov.; from the Derivation of name. Named after Charlie Underwood (Birkbeck Wordian (Guadalupian) Khuff Formation of the Haushi-Huqf College, London) in recognition of his important work on the area, central eastern Oman. taxonomy of the genus Lissodus.

Referred species. ‘Lissodus’ wirksworthensis Duffin, 1985; ‘Lissodus’ Holotype. One complete tooth (MPUM10891, Fig. 7A–D). pectinatus Lebedev, 1996; ‘Lissodus’ sp. in Ivanov (1996). Type locality. Haushi Cliff, Haushi-Huqf area, central eastern Diagnosis. Teeth with a mesio-distally expanded crown Oman. with a low profile and a strong crown shoulder and with up to four lateral cusplets. Moderately to well-developed Type stratum. Bioclastic limestone bed at 16 m height on com- labial peg, which may be accompanied by nodes towards posite log of Angiolini and Bucher (1999), sampled at section the base of the lateral cusplets and labial root buttress K1, Khuff Formation, Akhdar Group, Wordian (Guadalupian, sometimes present. Lingual peg sometimes present, middle Permian). although less developed than the labial peg. Variable ornamentation density, consisting of coarse cristae and Material. Sample AO40, Khuff Formation, yielded six complete specimens. Specimen used for SEM imaging: MPUM10891; base less porous than in other hybodontoids. remaining specimens: MPUM10899 (5). Remarks. This is a replacement genus for ‘Palaeozoic Genus Diagnosis. Triangular labial peg always present, some- 2’, as unofficially erected by Rees and Underwood (2002). times flanked by two accessory nodes, and lingual peg less They concluded that the Palaeozoic material referred to Liss- developed but always present. Acute longitudinal crest odus should be divided into two separate genera that were and horizontal rim present at crown shoulder, most pro- left in open nomenclature. Rees (2008) reorganized the nounced lingually. Base slightly dejected lingually. Anaula- Mesozoic hybodonts and ejected the genus Lissodus from the corhize vascularization consisting of few large foramina Lonchidiidae. It needs to be clarified whether the Palaeozoic with labially a single row of small foramina near the material is equal to that from the Mesozoic before its precise crown–base junction. systematic position can be decided. For Reesodus gen. nov., the erection of a new family is not warranted until the het- Description. The teeth are generally symmetrical and small (0.9– erodonty pattern, and the potential presence of enlarged lat- 1.2 mm mesio-distally, 0.3–0.5 mm labio-lingually, 0.4–0.5 mm eral teeth can be assessed (Rees 2008). Both genera must high). In apical outline, the teeth are elongate but may approach remain listed as family incertae sedis. Fischer (2008) advo- a triangular shape, and they are lingually concave in mesial or cated to retain the conservative view of Palaeozoic ‘Lissodus’ distal view. The crown–base junction is distinctly incised. The because of unsettled criticism, but Ginter et al. (2010) follow crown is low, about equal in height to the base, and the mesial

FIG. 7. Hybodont teeth from the Khuff Formation, Haushi Cliff, Haushi-Huqf area, central eastern Oman. A–D, Reesodus underwoodi gen. et sp. nov. MPUM10891, loc K1, sample AO40; tooth, holotype. A, lingual, B, labial, C, apical, and D, lateral views. E–P, Teresodus amplexus gen. et sp. nov. E–H, MPUM10888, loc K1, sample AO40; tooth, paratype. E, lingual, F, labial, G, apical, and H, lateral views. I–L, MPUM10889, loc K1, sample AO40; tooth, holotype. I, lingual, J, labial, K, apical, and L, lateral views. M–P, MPUM10890, loc K1, sample AO40; tooth, paratype. M, lingual, N, labial, O, apical, and P, lateral views. Q–T, cf. ‘Palaeozoic Genus 1’ sp. MPUM10932, loc K4, sample AO47bis; tooth. Q, lingual, R, labial, S, apical, and T, lateral views. U–X, Gunnellodus bellistriatus (Gunnell, 1933). U–V, MPUM10911, loc K4, sample AO55; tooth. U, anterior, and V, lateral views. W–X, MPUM10880, loc K1, sample AO40; tooth. W, anterior, and X, lateral views. All scale bars represent 300 lm. KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 317

A

B C

D E

F G

H I

J K

L M

N O

Q P

R

S

T

U W

V X 318 PALAEONTOLOGY, VOLUME 56 and distal parts are rounded to slightly pointed. The main cusp Palaeozoic genera can be rejected for the same reason (Zan- is distinct but low and inclines lingually. There may be up to gerl 1979; Wang et al. 2009), but Ginter et al. (2010) four pairs of lateral cusplets, but these remain low, are usually pointed out a similarity to Lissodus for both Dabasacanthus weakly developed and may be completely lacking. An acute lon- and Gansuselache and that the genera are in need of review. gitudinal crest traverses the apices of all cusps, positioned lin- The similarity to Lissodus is continued in the material stud- gually from the midline of the tooth in apical view. A weakly ied here, but generally only in crown morphology. The basal developed lingual peg and a moderate labial peg are present at the base of the main cusp, the latter of which is triangular in morphology is markedly different, most importantly in that labial outline and may possess two small accessory nodes when the porosity is much reduced. The differences in basal mor- more weakly developed. A clear horizontal rim is present at the phology are considered sufficient grounds to separate this height of the crown shoulder, which is most pronounced on the material from Lissodus s.s. Instead, it is included with ‘Palae- lingual face. The crown surface is smooth, with the exception of ozoic Genus 2’ of Rees and Underwood (2002), which is weak vertical cristae, which may be deflected along their course, here renamed, based on the presence of a strong crown connecting the circumferential rim with the longitudinal crest. shoulder, the ornamentation consisting of coarse cristae, the They are more pronounced and more numerous on the lingual presence of a moderate labial peg and the reduced porosity face. A consistent feature is the crista connecting the lingual peg of the base. The material can be separated from both named with the apex of the main cusp and often a pair of flanking species in Reesodus gen. nov. based on the presence of a lin- cristae. In the absence of lateral cusplets, there is no recognizable gual peg. Furthermore, Reesodus pectinatus (Lebedev, 1996) pattern, but in their presence, there is a crista connecting the apex of the cusplet with the rim at the crown shoulder. possesses strongly developed lingual accessory nodes, a The base shows a lingual protrusion, which is not equally well labial basal buttress but no labial peg, massive vertical labial visible in all teeth in apical view, due to a varying extent of lingual ridges, a well-developed main cusp and a deeply depressed displacement relative to the crown. The labial peg is not supported labial side (Lebedev 1996), and Reesodus wirksworthensis by a buttress. The lingual edge of the base has a lobed appearance (Duffin, 1985) displays a strong vertical ridge with accessory in lateral view. A small number of randomly located foramina of cusplet surmounting the labial peg, a labial base buttress varying sizes are present on the lingual face. On the labial face, few supporting the labial peg and any vertical ridges are smaller-sized foramina form a row on the upper part of the base restricted to the labial face of the crown, all of which are laterally, while centrally a couple of large foramina open labio- characters that are absent in the material described here. No basally, causing a corrugated appearance of the labial base edge. A specific morphological description is provided by Ivanov weakly developed sulcus is present basolabially, but is often later- (1996) for his indeterminate material, but he does state that ally restricted with the labial base edge remaining low throughout. The vascularization type is anaulacorhize. it shows affinity with some varieties of Reesodus wirksworth- ensis. Indeed, similarities can be observed when comparing Remarks. Hybodontiform tooth morphology is extremely it to P. 60748 (Duffin 1985, text-fig. 21) and in particular varied and accommodates low-crowned teeth (Ginter et al. with regard to the presence of lingual nodes. This also forms 2010), which is typical of this material. The enameloid the basis for differentiating it from the species named here, microstructure has not been examined for the presence of a which possesses a smooth lingual outline in apical view. monolayer of single crystallites (SCE) due to the limited nature of the material, but the anaulacorhize vascularization Genus TERESODUS gen. nov. of the base is in accordance with hybodontiform character- istics (Ginter et al. 2010). This material fits the familial diag- Derivation of name. Derived from the Latin teres ‘smooth, ele- nosis of the Lonchidiidae of Rees and Underwood (2002) in gant’ and the ancient Greek odous ‘tooth’. most aspects, but a significant difference in basal morphol- ogy (i.e. few foramina) prevents direct inclusion of the Type species. Teresodus amplexus gen. et sp. nov.; from the Wor- material within this family. Nevertheless, a close relation- dian (Guadalupian) Khuff Formation of the Haushi-Huqf area, ship is assumed, so the genera associated with this family central eastern Oman. have been assessed. Dabasacanthus and Gansuselache are restricted to the Palaeozoic, and Vectiselachos, Hylaeobatis, Diagnosis. Moderately heterodont dentition with asymmet- Parvodus and Lonchidion are restricted to the Mesozoic. rical lateral teeth, low crown profile and moderately incised Lissodus, which was only recently ejected from this family crown–base junction. Main cusp low, smooth and lingually (Rees 2008), is well established in the Mesozoic, but has directed. Longitudinal crest present, as well as a circumfer- poorly known Palaeozoic representatives, which are divided ential rim at the crown shoulder, but crown surface generally into two genera left in open nomenclature (Rees and smooth. Moderate lingual peg, surmounted by 2–4 weak Underwood 2002). The Mesozoic genera can be rejected vertical ridges. Labial crown face concave in anterior based on clear differences in morphological characters of teeth, but convex laterally. Small labial peg present in both crown and base (Rees and Underwood 2002). The (antero)lateral teeth, but may be absent in anterior teeth. KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 319

Lingual flexure of mesial and distal crown extremities most cusplets is generally moderately developed in anterior teeth, pronounced in lateral teeth. One pair of lateral cusplets which may be somewhat angular in appearance and in some present in anterior teeth, but gradually weaker to absent in cases distinctly projected lingually. In (antero)lateral teeth, the (antero)lateral teeth. Base with slight lingual protrusion. pair of lateral cusplets is much more weakly developed and most Anaulacorhize vascularization with few randomly located often completely absent. A small, seemingly triangular, labial peg is present, in some cases flanked by two accessory nodes, but foramina and labially a row of small foramina near the weakly developed or even absent in anterior teeth. The teeth also crown–base junction. Basolabial sulcus always present. possess a moderate lingual peg, which is always larger than the labial peg, with a strong surmounting crista connecting the lin- Distribution. Central eastern Oman. gual peg with the apex of the main cusp and sometimes also 2–4 weak accessory vertical cristae. A moderately acute longitudinal Stratigraphical range. Wordian, Guadalupian, middle Permian. crest traverses the entire length of the teeth, but is positioned lingually from the midline of the teeth in apical view. A circum- ferential rim is also present at the crown shoulder, which is Teresodus amplexus sp. nov. more pronounced lingually, and the crown–base junction is Figure 7E–P moderately incised. The crown surface is generally smooth, but may show slight cristae and crenulations lingually. Derivation of name. Derived from the Latin amplexus ‘embrace’. The base is characterized by anaulacorhize vascularization with on the lingual face a small number of foramina that are positioned Holotype. One complete tooth (MPUM10889, Fig. 7I–L). in a row-like manner and which are enlarged centrally. A central labiobasal sulcus is present, and foramina are present in two rows, Paratypes. Two complete teeth (MPUM10888, Fig. 7E–H; which may extend over the entire width of the teeth or may be MPUM10890, Fig. 7M–P). restricted to the central part. The row near the crown–base junc- tion consists of small foramina, and the second row consists of lar- Type locality. Haushi Cliff, Haushi-Huqf area, central eastern ger foramina opening at the upper edge of the sulcus. The base Oman. protrudes slightly beyond the crown lingually.

Type stratum. Bioclastic limestone bed at 16 m height on com- Remarks. The presence of anaulacorhize vascularization posite log of Angiolini and Bucher (1999), sampled at section indicates a close relationship with the Hybodontiformes, K1, Khuff Formation, Akhdar Group, Wordian (Guadalupian, and a mildly heterodont dentition is also common within middle Permian). the order (Ginter et al. 2010). Distinct differences exist with Omanoselache gen. nov., especially with regard to the cus- Material. Samples AO40, AO55, AO47bis, AO50, Khuff Forma- plet pattern, as well as the lingual flexure of the crown, the tion, yielded 103 complete and broken specimens. Specimens circumferential rim at the crown shoulder and, most used for SEM imaging: MPUM10888 (anterior), MPUM10889 importantly, the very distinct lateral crown outlines of both (anterolateral), MPUM10890 (lateral); remaining specimens: genera. Rather, a closer relationship is assumed with the MPUM10900 (69), MPUM10920 (14), MPUM10939 (14), group previously known as the ‘Polyacrodontidae’ (Rees MPUM10950 (3). 2008). For example, ‘Polyacrodus’ dentitions have been described as being heterodont, consisting of blunt, multi- Diagnosis. As for genus. cuspid teeth with a flat base and basolabial sulcus. Further- Description. The teeth are gracile (1.1–1.3 mm mesio-distally, more, lingual flexure of lateral crown extensions and a 0.3–0.4 mm labio-lingually, 0.5–0.6 mm high, but (antero)lateral circumferential rim at the crown shoulder have also been teeth may be slightly larger and especially mesio-distally, in known to occur within the ‘Polyacrodontidae’ (Ginter et al. which direction they can reach dimensions of over 2 mm) and 2010). However, the ‘Polyacrodontidae’ are in need of slightly to moderately arched mesio-distally. They form part of a review, and ‘Polyacrodus’ still remains without a valid (dif- dentition displaying gradient monognathic heterodonty involv- ferential) diagnosis (Rees 2008). The circumferential rim at ing a number of crown features. Anterior and anterolateral teeth the crown shoulder is a typical feature of ‘Polyacrodus’ con- are symmetrical, whereas lateral teeth are asymmetrical to a trarius Johns, Barnes and Orchard, 1997 (general crown varying degree. The crown is low, about equal in height to the shape of this material reminiscent of Type A) and ‘Polyacr- base, and the mesial and distal parts are rounded. The main odus’ bucheri Cuny, Rieppel and Sander, 2001, which have cusp is low, smooth and lingually directed. In anterior teeth, the been assigned tentatively to the Homalodontidae (Mutter labial crown face is concave, potentially indicative of an inter- locking tooth arrangement. (Antero)laterally, the labial crown et al. 2007, 2008). However, this rim is not included in the face is slightly to distinctly convex. The mesial and distal crown diagnosis of the Homalodontidae or in Homalodontus. The extremities show lingual flexure in apical view. This is best material is also comparable, to an extent, to ‘Lissodus’ developed in lateral teeth and is only intermediate to slight in (‘Polyacrodus’) zideki Johnson, 1981. Teeth of this species anterolateral and anterior teeth, respectively. One pair of lateral are also moderately heterodont, with a symmetrical crown 320 PALAEONTOLOGY, VOLUME 56 and a thicker labial side. Furthermore, teeth of ‘L’. zideki described in the emended diagnosis by Rees and are described as arcuate (both in lateral and apical view), Underwood (2002), which include a small tooth size even though it is described as most distinct in anterior teeth (<5 mm), a low coronal profile, a larger mesio-distal and less so in lateral to posterior teeth. Further similarities dimension than the height of the tooth and a base subequal are in the presence of a longitudinal crest, well-developed in depth to the crown. More defining characters include lingual process, a basolabial sulcus, specialized foramina the presence of a well-developed labial peg and anaulacorh- and a circumferential rim at the height of the crown shoul- ize vascularization with a line of differentiated vascular der (although this character is not included in the original foramina on the upper part of the labial basal face. The description or diagnosis). Nevertheless, major differences Palaeozoic lonchidiid genera listed in Ginter et al. (2010) also exist, which include the monocuspid character of are Lissodus, Dabasacanthus and Gansuselache. Inclusion ‘L’. zideki, the well-developed transverse crest, the consis- with Gansuselache is not supported based on discrepancies tent presence of a well-developed labial peg and the large with the prominent vertical ridges and the absence of a sin- number of foramina in the base. Awaiting revision of the gle row of small foramina labially, which typify the genus. ‘Polyacrodontidae’, this material must remain listed as Dabasacanthus also has to be discounted, based on the family incertae sedis. much smaller size of the teeth and the longitudinal crest running along the midline, but is generally also not war- ranted due to the lack of reliably described characters and Genus cf. ‘PALAEOZOIC GENUS 1’ Rees and Underwood, the genus being in need of review. The tooth is most similar 2002 to Lissodus, a genus well established in the Mesozoic but with poorly known Palaeozoic representatives, divided into cf. ‘Palaeozoic Genus 1’ sp. two genera erected by Rees and Underwood (2002) as Figure 7Q–T Palaeozoic counterparts of Lissodus. Of these, the specimen described here shows most affinity with ‘Palaeozoic Genus Material. Sample AO47bis, Khuff Formation, yielded one com- 1’ and therefore with ‘Lissodus’ zideki (Johnson, 1981) and plete specimen. Specimen used for SEM imaging: MPUM10932. potentially with ‘Lissodus’ lacustris (Gebhardt, 1988). This is observed in the following characters: non-ornamented Description. Robust tooth with a compact appearance (1.6 mm crown, prominent occlusal crest, symmetry, absence of cus- mesio-distally, 0.7 mm labio-lingually, 1.1 mm high) and a tri- plets, wide labial peg, triangular to diamond-shaped outline angular outline in lingual and labial view, but also in apical in occlusal view due to the potential presence of a lingual view. Both crown and base are mesio-distally arched. The crown peg, rare crown ornamentation, more porous base than in is of about the same height as the base, remains low and pos- ‘Palaeozoic Genus 2’ and presence of small, circular foram- sesses very rounded extremities. The bluntly pointed main cusp ina near the crown–base junction. However, the specimen is massive, and the extremities of the tooth fall away laterally at differs from ‘Palaeozoic Genus 1’ in that it does not possess roughly the same angle as the mesial and distal sloping faces of the main cusp. Lateral cusplets are absent. There is a small, but a lingually projected base and labially inclined cusp, the robust lingual peg, which is minor compared with the massive latter of which is one of the features highlighted as falling labial peg. The latter accounts for almost one-third of the maxi- outside the range of Lissodus s.s. (Rees and Underwood, mum labio-lingual dimension of the tooth. A longitudinal crest 2002). Also contributing towards the separation of ‘Palaeo- is developed, which is positioned slightly lingually off the mid- zoic Genus 1’ from Lissodus is the heterodonty pattern, line of the crown in apical view, causing the labial crown face to which cannot be assessed from the material currently under be sloping while the lingual face is near-vertical. Straight, but study due to its limited nature, and the lack of lateral cus- very short cristae – only reaching around 80 lm in length – plets, which does again correspond to the tooth described originate at the longitudinal crest and extend labially. They are here. Since a straightforward conclusion is not possible, the coarse and few in number (6–7 on each extremity). The rest of tooth remains listed as cf. ‘Palaeozoic Genus 1’ and would the crown surface is smooth. A longitudinal rim is present at the be the youngest specimen of this genus. crown shoulder, which is only discontinued on the pegs. The base follows the same apical outline as the crown, with- out any protrusions. A labial buttress supports the labial peg. A Order HYBODONTIFORMES? moderate number of randomly located foramina perforate the base. They are of varying size, but tend to be larger in the cen- tral part. Labially, a row of foramina is positioned close to the Genus GUNNELLODUS Wilimovsky, 1954 crown–base junction and extends across the buttress. The vascu- Type species. Idiacanthus bellistriatus Gunnell, 1933; from the larization type is anaulacorhize. Pennsylvanian Kansas City Group of Missouri, USA.

Remarks. Referral of this material to the Lonchidiidae can Diagnosis. Cusp sub-elliptical in cross-section, gently be argued based on correspondence to the features arched posteriorly and gradually tapering from the base to KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 321 an acute apex. Crown surface densely ornamented with Articulated elements are not positioned directly next to each numerous, coarse cristae, starting at the base. Not all cristae other but occur in a more ‘stacked’ fashion where the larger reach the apex, but taper out lower on the cusp. No true posterior-most element is tilted further backward and its base anastomosing occurs. Base rounded in outline and porous sits on top of the posterior portion of the base of the preceding with flat to concave basal surface. May occur in articulated element. The anterior side of the base is less developed and partly envelops the crown and base of the smaller element. The state consisting of up to four elements that are of decreas- crowns are also flattened and less ornamented on the articulated ing size anteriorly. Base more irregular in shape in articu- surfaces. The articulated elements are observed most often in lated specimens (emended from Gunnell 1933). pairs, but may consist of up to four elements, which are of sig- nificantly increasing size posteriorly. Remarks. The genus is here reduced to a monospecific genus, since the characteristics used for specific separation Remarks. This material is assigned to Gunnellodus, because were deemed trivial and attributable to natural variation. it displays all the characteristics that were diagnosed by The type species remains intact. Gunnell (1933) for the genus. The features that he used to distinguish between the three species of Gunnellodus are deemed trivial, and G. bellistriatus is chosen as the only Gunnellodus bellistriatus (Gunnell, 1933) valid species. These elements are here interpreted tenta- Figures 7U–X, 10K tively as part of a hybodont pharyngeal tooth whorl, similar to those described for Hamiltonichthys mapesi Maisey, 1933 Idiacanthus bellistriatus Gunnell, pp. 293–294, pl. 31, 1989. Maisey (1989) initially placed the tooth whorls in a fig. 60. symphyseal (mandibular) position, but following prepara- 1933 Idiacanthus cameratus Gunnell, p. 294, pl. 32, fig. 29. tion of additional specimens he concluded that they were 1933 Idiacanthus sp. Gunnell, p. 294, pl. 33, figs 39, 41. actually a series of pharyngeal tooth whorls. No tooth 1933 Idiacanthus trispinosus Gunnell, p. 294, pl. 33, fig. 46. 1954 Gunnellodus Wilimovsky, p. 693. whorl positioned in the jaw has ever been described in any hybodont, and H. mapesi is the only species for which pha- Material. Samples AO40, AO55, AO47bis, AO50, Khuff Forma- ryngeal tooth whorls have been described. The pharyngeal tion, yielded 254 singular and articulated tooth specimens, both dentition described here is similar to that of H. mapesi complete and broken. Specimens used for SEM imaging: based on a number of characteristics, including acuminate, MPUM10911 (singular), MPUM10880 (articulated); remaining recurved cusps and small tooth whorls (<2 mm), but a lim- specimens: MPUM10895 (75), MPUM10916 (111), MPUM10935 ited number of cusps per whorl and a denser ornamenta- (53), MPUM10948 (13). MPUM11051 from AO214 was imaged tion differentiates it from H. mapesi pharyngeal teeth. If with light microscopy for additional observations. the interpretation of the material as pharyngeal teeth is cor- rect, it is likely that they belong with one of the other hyb- Referred species. Gunnellodus cameratus (Gunnell, 1933); Gunnello- odont taxa present in the assemblage. It is not possible to dus sp. (Gunnell, 1933); Gunnellodus trispinosus (Gunnell, 1933). identify the precise taxon with the available material, so the genus remains listed as Hybodontiformes incertae sedis, like Diagnosis. As for genus (emended from Gunnell 1933). Hamiltonichthys, pending future study. In contrast, Hoff- man and Hageman (2011) suggested a stethacanthid (sym- Description. Unusual elements that occur in articulated and sin- moriiform) relationship for Gunnellodus, which they gular state. Isolated elements are small but highly cusped (0.4– 1 mm mesio-distally (at base), 0.7–1 mm antero-posteriorly (at interpret as comprising cranial cap and brush denticles and base), 1.5 mm high, although few specimens reaching up to buccopharyngeal denticles. This is supported by the obser- 3 mm high do occur). The base is shaped like a rounded oval in vation that Gunnellodus is recovered both as isolated ele- apical view, and the crown may be somewhat displaced posteri- ments and in articulated state with fused bases, whereas orly on the base, creating a seemingly anterior protrusion of the whorls of H. mapesi have only been recovered intact. How- base. The crown consists of a single large cusp with an acute ever, Hoffman and Hageman (2011) also mention that this apex and a dense ornamentation pattern, which is composed of type of material is normally found in conjunction with prominent vertical cristae that run along the entire length of the stethacanth-like cladodont teeth and tooth whorls. Only cusp and end just below the apex. Some cristae only reach about Glikmanius culmenis gen. et sp. nov. displays stethacanth- one-third of the way up and approach a continuing crista before like features in crown morphology, as well as similarities in ending, but they do not truly anastomose. The cusp is about crown ornamentation with Gunnellodus, but its basal mor- twice as wide antero-posteriorly than mesio-distally and dis- tinctly curved posteriorly. The base is rounded in apical outline, phology prevents inclusion with the Symmoriiformes. Both possesses a flat to concave basal surface and is about one-third hypotheses remain possible, but because a clear hybodont the height of the cusp. Few small foramina are randomly located relationship has been recorded from articulated H. mapesi on every part of the base. remains and hybodonts are abundantly represented in the 322 PALAEONTOLOGY, VOLUME 56

Khuff fauna, whereas the stethacanthid relationship is Diagnosis. Main cusp moderately high and strongly labio- merely suggested, a hybodont affinity is currently consid- lingually asymmetrical, flanked by 2–3 pairs of blunt, sub- ered the most parsimonious. conical lateral cusplets; weak lingual peg present, sur- mounted by a weak crista and two flanking cristae; small labial node may be present; crown surface smooth or Order INCERTAE SEDIS weakly ornamentated with few vertical cristae; longitudinal Family SPHENACANTHIDAE Maisey, 1982 rim at the crown shoulder both lingually and labially.

Genus KHUFFIA gen. nov. Description. Elongate teeth that appear thin in apical view (1.0– 1.2 mm mesio-distally, 0.3–0.4 mm labio-lingually, 0.5–0.6 mm high) and slightly to moderately arched mesio-distally. Slight Derivation of name. Derived from ‘Khuff’, the rock formation of heterodonty is present, and symmetrical anterior teeth and origin. slightly asymmetrical lateral teeth can be distinguished. The labial side is straight to very slightly concave, whereas the lingual Type species. Khuffia lenis gen. et sp. nov.; from the Wordian side is distinctly convex, and the mesial and distal extremities (Guadalupian) Khuff Formation of the Haushi-Huqf area, cen- are very rounded. A hint of lingual flexure can be observed in tral eastern Oman. the anterior teeth. The crown is generally low, but still usually exceeds the height of the rather shallow base. The main cusp is Diagnosis. Teeth with a crown that is moderately inclined moderately high and lingually inclined. It is also almost always lingually; main cusp flanked by up to three pairs of lateral distally slanted in lateral teeth. In lateral teeth, three pairs of lat- cusplets; cutting edge not interrupted between cusp and eral cusplets that are of laterally decreasing height are developed cusplets; main cusp asymmetrical labio-lingually with a whereas in anterior teeth there are only two pairs. They remain strongly convex lingual face and a flatter labial one; orna- lower in lateral teeth, but in both tooth types the outermost pair mentation of the crown absent or weak; base firmly attached is weakly developed. The cusplets are blunt and subconical, well to the crown, generally shallow, but can attain up to 40 per separated and straight, but lingually inclined. At the base of the cent of the height of the crown and with a moderate lingual main cusp, a weak lingual peg is developed with a weak sur- projection; reduced number of foramina, up to 10, large but mounting crista and two flanking cristae, and labially a small node may be present. The crown surface may be nearly smooth, irregular in size, crossing the root labio-lingually. but often the ornamentation consists of a few weak and coarse vertical cristae on both the labial and lingual sides. A longitudi- Distribution. Central eastern Oman. nal crest is present, as well as a longitudinal rim at the height of the crown shoulder, which is most pronounced lingually. Stratigraphical range. Wordian, Guadalupian, middle Permian. The base protrudes lingually and is perforated by randomly located foramina of varying size, which is typical of anaulacorh- ize vascularization. Lingually, the foramina are enlarged in the Khuffia lenis sp. nov. central part, and the smaller foramina on either side may be Figure 8A–H absent. On the labial side, a basal sulcus is present and also two rows of foramina: one row of large foramina on the basolabial Derivation of name. Derived from the Latin lenis ‘gentle, edge of the sulcus and one discontinuous row of small foramina smooth’. near the crown–base junction, the latter of which may be entirely absent. Holotype. One complete tooth (MPUM10882, Fig. 8E–H). Remarks. Anaulacorhize vascularization and a tooth mor- Paratype. One complete tooth (MPUM10881, Fig. 8A–D). phology reminiscent of Hybodus Agassiz, 1837, suggest hyb- odontiform affinities. However, the diagnosis of the Type locality. Haushi Cliff, Haushi-Huqf area, central eastern Hybodontidae (sensu Maisey 1987) only relates to teeth Oman. with an anaulacorhize basal platform and tumid to multi- cuspid crown, and the generic diagnosis also merely states Type stratum. Bioclastic limestone bed at 16 m height on com- that the dentition contains multicuspid acuminate teeth posite log of Angiolini and Bucher (1999), sampled at section with osteodont crowns and does not specify any further K1, Khuff Formation, Akhdar Group, Wordian (Guadalupian, characteristics (Maisey 1987). Furthermore, there is cur- middle Permian). rently no valid Palaeozoic representative of Hybodus and the Palaeozoic material that was initially assigned to the Material. Samples AO40, AO55, AO47bis, Khuff Formation, genus, which is mainly from the Carboniferous of Europe yielded 79 complete and broken specimens. Specimens used for and the USA, has since been reassigned to Sphenacanthus SEM imaging: MPUM10881, MPUM10882; remaining speci- Agassiz, 1837, or Fadenia Nielsen, 1932 (Ginter et al. 2010). mens: MPUM10901 (74), MPUM10921 (2), MPUM10940 (1). KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 323

B

C A

D

E

F G

H

J

I K

L

M

N O

P

S R Q

T

FIG. 8. Euselachian teeth from the Khuff Formation, Haushi Cliff and Saiwan, Haushi-Huqf area, central eastern Oman. A–H, Khuffia lenis gen. et sp. nov. A–D, MPUM10881, loc K1, sample AO40; tooth, paratype. A, lingual, B, labial, C, apical, and D, lateral views. E–H, MPUM10882, loc K1, sample AO40; tooth, holotype. E, lingual, F, labial, G, apical, and H, lateral views. I–L, Khuffia prolixa gen. et sp. nov. MPUM10892, loc K1, sample AO40; tooth, holotype. I, lingual, J, labial, K, apical, and L, lateral views. M–T, Euselachii gen. et sp. indet. M–P, MPUM10931, loc K4, sample AO47bis; tooth. M, lingual, N, labial, O, apical, and P, lateral views. Q–T, MPUM11045, loc Saiwan, sample AO123; tooth. Q, lingual, R, labial, S, apical, and T, lateral views. All scale bars represent 300 lm. 324 PALAEONTOLOGY, VOLUME 56

Inclusion of the new material with Fadenia is not sup- main cusp; lingual or labial pegs absent; crown surface ported, because Fadenia’s dentition consists of tumid and often weakly ornamented with fine striae; strong longitu- pavement teeth with much enlarged symphysial teeth, dinal rim lingually at the crown shoulder. which are bulbous and tumid (Mutter and Neuman 2008). Instead, there are many more similarities to teeth of Sphe- Description. Generally symmetrical teeth that are slender, elon- nacanthus, a genus mostly known from fin spines. The gen- gate (1.3–1.6 mm mesio-distally, 0.3–0.5 mm labio-lingually, eric diagnosis by Dick (1998) includes the presence of a 0.7–0.8 mm high) and slightly mesio-distally arched. The labial heterodont dentition, anterior teeth with a moderately high side is concave, which is most distinct in the central part, median cusp and 1–4 pairs of lateral cusplets, and posterior whereas the lingual side is convex. The main cusp is high and may be slanted distally. The well-separated 1–2 pairs of lateral teeth lacking well-developed cusps. Further similarities are cusplets display laterally decreasing height and may curve slightly present in the diagnosis for S. carbonarius, which includes towards the main cusp. All cusps are lingually inclined, with the laterally decreasing size of lateral cusplets, cristae appearing labial face most steeply sloping. No lingual or labial pegs are on all cusps but weak in mesial teeth and a flat or slightly developed, but an acute longitudinal crest is present. The crown concave basal face (Soler-Gijo´n 1997). Ginter et al. (2010) surface ornamentation often consists of fine striae on all cusps, add that a distally inclined main cusp may occur in this which may be stronger developed on the lingual side, but the species. The similarities with S. serrulatus, the type species, crown surface may also be nearly smooth. A strong longitudinal include a general symmetry with possible slight asymmetry, rim is developed lingually at the height of the crown shoulder. blunt cusp apices, an occlusal crest occurring in smaller The base protrudes lingually and is perforated by few foramina teeth, a shallow base and no distinct pattern in the position of varying size, generally enlarged centrally, on the lingual side. of the foramina, except a longitudinal row often occurring On the labial side, small foramina are organized in a discontinu- ous row-like fashion near the crown–base junction. A mesio-dis- labially (Ginter et al. 2010). The differences start with the tally wide basolabial sulcus is present and a row of large foramina ornamentation of the crown surface. In Sphenacanthus, open at the labial edge. The vascularization type is anaulacorhize. coarse vertical ridges appear both lingually and labially, and this ornamentation is much weaker in our material or often Remarks. The material described here possesses hybodonti- entirely absent. In addition to this, the lateral cusplets are form characteristics such as anaulacorhize vascularization better separated in the specimens described here, the base is and a tooth morphology reminiscent of Hybodus Agassiz, deeper, its lingual projection is less extensive and the 1837. It is also similar to Khuffia lenis gen. et sp. nov. in foramina are larger and fewer in number. To accommodate many respects, including a lingually inclined crown, less these differences, a new genus is erected, which is believed than three lateral cusplet pairs, a continuous longitudinal to be closely affiliated with Sphenacanthus. crest, a generally shallow base with lingual projection and a reduced number of foramina. The same arguments against inclusion with Hybodus and Fadenia Nielsen, 1932, are valid, Khuffia prolixa sp. nov. and a close affinity with Sphenacanthus Agassiz, 1837, is very Figure 8I–L likely, based on characteristics described by Dick (1998), Soler-Gijo´n (1997) and Ginter et al. (2010). Inclusion of the Derivation of name. Derived from the Latin prolixus ‘wide out- material within Sphenacanthus is rejected, however, based standing’. on the following differences: finer and less dense ornamenta- Holotype. One complete tooth (MPUM10892, Fig. 8I–L). tion, lateral cusplets better separated from the main cusp, deeper base with more restricted lingual projection and Type locality. Haushi Cliff, Haushi-Huqf area, central eastern fewer and larger foramina, and the material is assigned to Oman. Khuffia instead. It can be separated from K. lenis, mainly based on the higher crown, the absence of lingual and labial Type stratum. Bioclastic limestone bed at 16 m height on com- pegs, the finer ornamentation and the wide separation of the posite log of Angiolini and Bucher (1999), sampled at section first lateral cusplet pair from the main cusp. K1, Khuff Formation, Akhdar Group, Wordian (Guadalupian, middle Permian). Family INCERTAE SEDIS Material. Sample AO40, Khuff Formation, yielded 27 complete and broken specimens. Specimen used for SEM imaging: Gen. et sp. indet. MPUM10892; remaining specimens: MPUM10902 (26). Figure 8M–T

Diagnosis. Main cusp high and weakly labio-lingually Material. Samples AO55, AO47bis, AO50, AO123, Khuff Forma- asymmetrical, flanked by 1–2 pairs of moderately high, tion, yielded ten complete and broken specimens. Specimens subrounded lateral cusplets widely separated from the used for SEM imaging: MPUM10931 (anterior), MPUM11045 KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 325

(posterior); remaining specimens: MPUM10922 (4), (2010) explain how the Protacrodontidae are an artificial MPUM10941 (3), MPUM10951 (1). group, the dentition of which cannot really be distin- guished from the hybodonts without additional material Description. Elongate and nearly symmetrical teeth (1.8–2.0 mm such as articulated specimens. Protacrodont-like dentitions mesio-distally, 0.5 mm labio-lingually, 0.5–1.1 mm high) that that have previously been referred to as hybodonts include show arching in the crown of anterior teeth. In apical view, the Sphenacanthus (contradictorily listed as Euselachii incertae mesial extremity may be pointed somewhat labially. In anterior sedis in the remainder of Ginter et al. 2010’s work) and teeth, the main cusp is about twice the height as the rest of the crown, slightly lingually directed and may be distally slanted. ‘Polyacrodus’. We disagree with the generally applied strati- From one to three pairs of lateral cusplets are always present, graphic ‘solution’ of assigning Devonian-age specimens of which remain low and are not well separated. They are of almost this design to the protacrodontids and later teeth to the hy- equal height, but generally show a decrease laterally. Posterior bodonts; so until a comparative morphological study has teeth remain low with the crown about equal in height to the resolved the systematic position of these groups, the taxon base lingually, but two-thirds of the total tooth height labially. remains listed as Euselachii incertae sedis. The main cusp is very much reduced and indistinguishable from the numerous lateral cusplets, which are of equal height, remain low and are not well separated. A longitudinal crest, acute in Subcohort NEOSELACHII Compagno, 1977 anterior teeth and blunt in posterior teeth, is developed travers- Family ANACHRONISTIDAE Duffin and Ward, 1983 ing all cusps, and a distinct circumferential rim is present at the crown shoulder, but may be stronger developed lingually. In Genus COOLEYELLA Gunnell, 1933 more ornamented teeth, a row of small nodes may be developed at the crown shoulder on the entire circumference, but is more pronounced labially. Type species. Cooleyella peculiaris Gunnell, 1933; from the Penn- A small lingual peg is developed at the base of the main cusp sylvanian Kansas City Group in Missouri, USA. in anterior teeth, with a strong surmounting crista connecting it to the apex and one flanking pair of weaker cristae. The rest of the crown surface is often characterized by dense ornamentation Cooleyella cf. fordi (Duffin and Ward, 1983) on all cusps; lingually, it consists of straight cristae and labially Figure 9A–D of more numerous wavy cristae that are of varying strength and length, most of which end in or near the cusp apices. Some 1983 Anachronistes fordi Duffin and Ward, pp. 95–98, anastomosing occurs. pl. 13, figs 1–10; pl. 14, figs 1–7, 9; text-figs 2A, 3D. The base protrudes lingually beyond the crown, whereas the 1996 Cooleyella fordi Duffin et al., p. 239. labial face is straight. A mesio-distally wide and deep basolabial sulcus is developed. The base is perforated by randomly located Material. Samples AO50, AO214, Khuff Formation, yielded two foramina, which are of varying size lingually. On the labial face, complete specimens. Specimen used for SEM imaging: a (sometimes discontinuous) row of small foramina is present MPUM10945; remaining specimen: MPUM11055. near the crown–base junction and larger foramina are positioned within the sulcus. The vascularization type is anaulacorhize. Description. MPUM10945 is an unusual and low tooth (1.1 mm mesio-distally, 0.6 mm labio-lingually, 0.5 mm high) that shows Remarks. These specimens are of protacrodont design asymmetry in the crown. In apical view, the tooth is triangular rather than the typical hybodont type. This suggests in outline, with a straight lingual face. The main cusp is low and inclusion in the Protacrodontidae, which was named by positioned about a quarter of the mesio-distal length of the Cappetta et al. (1993), but not defined. Ginter et al. tooth off the centre of the base. It is somewhat lingually inclined (2010) described the dental features of this family. Simi- and distally slanted. On the mesial extremity, a well-developed larities between the material described here and protacr- triangular lateral blade is present, whereas the distal extremity is odontid teeth include a low, pyramidal main cusp and 1– thinner labio-lingually and turned downwards. A prominent 3 smaller lateral cusplets, which are similarly shaped and labial visor is developed, which is laterally expanded and dis- tinctly overhangs the crown–base junction. Lateral cusplets are fused in the lower part. Also similar are the labio-lin- absent. Besides a slight longitudinal crest near the lingual edge gually compressed and lingually inclined crown, with a and a very irregular ridge on the labial edge of the blades, the general ornamentation pattern consisting of coarse, crown surface is smooth. straight or wavy cristae that reach the cusp apices and a The base protrudes beyond the crown laterally and lingually, laterally elongated base with almost no lingual extension causing the straight lingual face to be large. The base becomes and rows of foramina. The specimens can be distin- less in depth labially, but possesses a distinct, downturned labial guished from the hybodontiform and other euselachian buttress supporting the labial visor, which is separated from the groups described in this study, because the cusps are not rest of the base by a central vascular pit. One large vascular well separated, as is usual in the other taxa, and the orna- canal penetrates the base horizontally over a short distance from mentation is much more wavy and dense. Ginter et al. the base of the lingual face (medio-external foramen) to the 326 PALAEONTOLOGY, VOLUME 56

C

B

A D E F G

H

J

K

I

L

M

N O

P

Q R S

V T

U

W KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 327 centre of the basal face (medio-internal foramen). This is typical Order SYNECHODONTIFORMES Duffin and Ward, 1993 of hemiaulacorhize vascularization. The crown of MPUM11055 differs in that it is near-symmet- Remarks. The Synechodontiformes are currently no rical, and the longitudinal crest is distinctly offset labially, longer classified with the Galeomorphii, as listed in which is also true for the much reduced main cusp. The labial Cappetta (1987), nor with the Squalomorphii, as listed flange is squarish in apical outline. The base shows clear signs in Ginter et al. (2010). Klug (2010) showed that the of wear. neoselachian order is ancestral to both these groups. Remarks. Several distinctive morphological characters sug- gest inclusion within the Anachronistidae, as defined by Family PALAEOSPINACIDAE Regan, 1906 Duffin and Ward (1983). These include prominent lateral blades, a labial visor strongly overhanging the crown–base Diagnosis. See Duffin and Ward, 1993, p. 58. junction and a well defined labial buttress separated from the rest of the base by a vascular pit. Other features indi- cate that the teeth should be included in one of the fam- Genus NEMACANTHUS Agassiz, 1837 ily’s two genera: Cooleyella Gunnell, 1933. These are small size (mesio-distal dimension below 2 mm), triangular to Type species. Nemacanthus monilifer Agassiz, 1837; from the trapezoidal apical outline, possible slight asymmetry in Rhaetian at Aust Cliff, England. the crown (paired with distally inclined central cusp), often rather compressed and lingually inclined central cusp, smooth crown surface lingually but often with a dis- Nemacanthus sp. continuous ridge along margins of visor and blades, lin- Figure 10A–E gual projection of the base and hemiaulacorhize vascularization (Ginter et al. 2010). The slight hetero- Material. Sample AO40, Khuff Formation, yielded two frag- donty that is generally present in the dentition (Ginter ments. Specimen used for imaging: MPUM10905; remaining et al. 2010) cannot be assessed because only two speci- specimen: MPUM10906 (1). MPUM11057 from another level of mens have been recovered. Three species are assigned to the Khuff Formation in the Haushi-Huqf area was imaged for Cooleyella. Inclusion of the best-preserved tooth with additional observations. C. amazonensis Duffin, Richter and Neis,1996, is not sup- ported based on the squarish outline of the labial visor in Description. Long and slender spine. Straight and laterally flat- this species, nor is inclusion with C. peculiaris Gunnell, tened, approximately 60 mm in length with pointed apex. 1933, based on the rounded outline of the labial visor Around 8 mm in largest antero-posterior dimension. Orna- (Ginter et al. 2010). Instead, all diagnostic characters of mented with an enameloid rib at the keel (starting at 15 mm from the base) and rounded enameloid tubercles on the lateral C. fordi (Duffin and Ward, 1983) are recognized, includ- faces, arranged in 11 straight vertical rows and with a sharp and ing a basal groove at the crown–base junction underneath postero-dorsally upward oblique lower limit (starting at 20 mm the labial visor and the downturning of the labial buttress, from the base anteriorly and 25 mm posteriorly, so intersecting as well as the triangular outline of the visor and the weak the normal on the long axis of the spine at an angle of around rim at the crown–base junction (lingually), as described 40 degrees). The posterior wall is concave with weakly developed in Ginter et al. (2010). However, the material is listed as denticles of the same appearance as the lateral tubercles at equal C. cf. fordi to accommodate the different position of the height on both edges, but is devoid of denticles centrally. The longitudinal crest in MPUM11055, which cannot be ade- small central cavity is of an oval shape and displaced posteriorly. quately assessed due to the worn nature of the tooth, and the limited number of recovered Cooleyella specimens Remarks. The most distinctive characteristics of these spine overall. fragments are the anterior enameloid rim and rounded

FIG. 9. Neoselachian teeth and euchondrocephalian tooth plates from the Khuff Formation, Haushi Cliff and Saiwan, Haushi-Huqf area, central eastern Oman. A–D, Cooleyella cf. fordi (Duffin and Ward, 1983). MPUM10945, loc K4, sample AO50; tooth. A, lingual, B, labial, C, apical, and D, lateral views. E–J, Neoselachii gen. et sp. indet. MPUM11024, loc unknown, sample AO38; tooth. E, lingual, F, labial, G, apical, and H, lateral views; I, enameloid fracture surface; J, detail enameloid layer. K–O, Petalodontiformes gen. et sp. indet. K, MPUM11054, loc Saiwan, sample AO214; tooth fragment. Section outline. L–O, MPUM11053, loc Saiwan, sample AO214; tooth fragment. L, lingual, M, labial, N, apical, and O, lateral views. P–S, Deltodus aff. mercurei Newberry, 1876. P–Q, MPUM10912, loc K4, sample AO55; tooth plate. P, apical, and Q, lateral views. R–S, MPUM10913, loc K4, sample AO55; tooth plate. R, apical, and S, lateral views. T–W, Solenodus cf. crenulatus Trautschold, 1874. MPUM11052, loc Saiwan, sample AO214; tooth plate. T, lingual, U, labial, V, apical, and W, lateral views. Scale bars represent A–H, 300 lm; I, 5 lm; J, 1 lm; K, 0.5 mm; L–O, 1 mm; P–S, 500 lm; T–W, 1 mm. 328 PALAEONTOLOGY, VOLUME 56

AB C

EF D

J

G H

I

M

K L

FIG. 10. Neoselachian fin spines, hybodont teeth and euchondrocephalian tooth plates from the Khuff Formation, Haushi Cliff and Saiwan, Haushi-Huqf area, central eastern Oman. A–E, Nemacanthus sp. A–C, E, MPUM10905, loc K1, sample AO40; dorsal fin spine fragment. A, lateral, B, lateral, and C, anterior views; E, cross-section. D, MPUM11057; dorsal fin spine fragment. Lateral view, detail. F–J, Amelacanthus cf. sulcatus (Agassiz, 1837). G–H, MPUM10907, loc K1, sample AO40; dorsal fin spine fragment. G, lateral, and H, lateral views. F, I–J, MPUM11058; dorsal fin spine fragments. F, cross-section, I, lateral view, and J, lateral view, detail. K, Gunnellodus bellistriatus (Gunnell, 1933). MPUM11051, loc Saiwan, sample AO214; articulated teeth. Lateral view. L–M, Solenodus cf. crenulatus Trautschold, 1874. MPUM11052, loc Saiwan, sample AO214; tooth plate. L, apical, and M, basal views. Scale bars represent A–D, 2 mm; E, 1 mm; F, 2 mm; G–H, 1 mm; I, 2 mm; J–M, 1 mm. enameloid tubercles arranged in vertical lines on the flanks. odontiformes; Cappetta 1987) and is closely allied to mate- These features, as well as lateral compression, a concave pos- rial that is currently assigned to Synechodus and terior wall and a posteriorly displaced central cavity fit with Palidiplospinax (Duffin and Ward 1993; Klug and Kriwet the general description of material that was formerly 2008). The material described in this study is identified as assigned to Nemacanthus, but which is currently separated Nemacanthus rather than Acronemus based on the differ- into two different monospecific genera with shared charac- ences between N. monilifer and A. tuberculatus as outlined ters: Acronemus and Nemacanthus.ForAcronemus tubercul- by Rieppel (1982). Nemacanthus spines are long and slender atus Rieppel, 1982, Maisey (2011) has shown that both (rather than short and stout) with a smaller number of hybodontiform and neoselachian features can be observed tubercles, arranged in up to 7–11 rows (rather than 9–23), in combination, leaving the phylogenetic relationship of this and a much more oblique enameloid limit of 60–78 degrees euselachian taxon unclear. Nemacanthus monilifer Agassiz, (rather than 8–24 degrees), which increases with ontogeny 1837, is classified within the Palaeospinacidae (Synech- (Rieppel 1982). Furthermore, the double row of denticles KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 329 on the posterior wall also fits with the description of Nem- Remarks. A close affinity of these teeth to the Anachronisti- acanthus (Cappetta 1987). dae is indicated by the presence of the following character- The oldest occurrences of Nemacanthus are as sp. indet. istics, as defined by Duffin and Ward (1983): lingually from the Lower Triassic of Spitsbergen (Stensio¨ 1921) inclined main cusp, well-developed lateral blades, a labial and Greenland (Stensio¨ 1932) and as N. elegans from the flange with tubercle situated underneath, a central vascular Lower Triassic of Idaho (Evans 1904; Maisey 1977). The pit and lingually expanded base. The deeply incised, pedes- identification of Nemacanthus here means a significant tal-like crown–base junction, as diagnosed for Ginteria range extension into the Palaeozoic. Duffin and Ivanov, 2008, causing the crown and base to be Numerous genera have been suggested to possess the well separated, add to the similarities. The crown further dentition matching the spines of Nemacanthus (Maisey shows similar morphological features to Cooleyella Gunnell, 1977), but no articulated body fossil has ever been recov- 1933, such as the obtuse main cusp in C. amazonensis ered. Most recently, Cuny and Risnes (2005) suggested an (Duffin, Richter and Neis 1996) and the rounded labial alliance between N. monilifer and the teeth of Rhomphaio- flange in C. peculiaris (Gunnell 1933, see Ginter et al. don nicolensis and R. minor (Synechodontiformes), because 2010). The teeth described here can, however, not be the taxa were almost always recovered in association. This is included within the Anachronistidae on the basis of the fol- not true, however, for the Khuff fauna, which lacks synech- lowing marked differences: presence of a row of foramina odontiform teeth of any kind, and the only neoselachian labially, which precludes the basal vascularization from taxon present is C.cf.fordi. The supposed phylogenetic being classed as hemiaulacorhize, which is diagnostic of the position of Nemacanthus may need to be reconsidered. family; much weaker development of the labial flange and related shallow nature of the vascular pit. Instead, the evi- dence suggests that the teeth stem from a less specialized Order INCERTAE SEDIS group that is potentially ancestral to the anachronistids. Among the Anachronistidae, Cooleyella has been observed Gen. et sp. indet. to possess a single crystallite enameloid (Chen et al. 2007; Figure 9E–J contra Duffin and Ward 1983), and Ginteria has been inter- preted to possess enameloid only from sections studied Material. Samples AO38, AO214, Khuff Formation, yielded two with light microscopy (Duffin and Ivanov 2008). Turner complete specimens. Specimen used for SEM imaging: and Young (1987) stated that Mcmurdodus White, 1968, is MPUM11024; remaining specimen: MPUM11050. covered with a shiny layer that may be enameloid, but a further study by Burrow et al. (2008) presented only very Description. Low teeth of unusual design (1.2 mm mesio-distally, questionable evidence of parallel-fibred enameloid. This 0.6 mm labio-lingually, 0.8 mm high). The crown and base are of study presents an undisputable observation of SCE in this about equal height and both massive. The crown surface is smooth new group, but it cannot elucidate its potential anachronis- and is covered by enameloid. An acute and lingually offset longitu- dinal crest is present, creating a transverse ridge between the two tid affinities. lateral blades, which curves lingually in the central part of the teeth to traverse a low, lingually directed (almost horizontal) main cusp. Lateral cusplets are absent. The lingual face of the crown is small Genus AMELACANTHUS Maisey, 1982 and almost vertical, whereas the lateral face of the crown is expanded and gently sloping, triangular in shape (in apical view), Type species. Onchus sulcatus Agassiz, 1837; from the lower slightly concave and possesses a weak, rounded labial flange. The Carboniferous Limestone of Gloucestershire and Shropshire, crown–base junction is deeply incised. England, and Armagh, Ireland. The base is pedestal-like, expanded lingually and less in mesio-distal width compared with the crown. The basal face is flat to slightly concave. An incipient basal tubercle is situated Amelacanthus cf. sulcatus (Agassiz, 1837) underneath the labial flange and is positioned over a very shal- Figure 10F–J low basal vascular pit. The lingual basal face is perforated by two to three large foramina. On the labial face, five foramina are 1837 Onchus sulcatus Agassiz, vol. 3, p. 8, pl. 1, fig. 6. organized in a row-like manner, and in the most structured pat- 1883 Ctenacanthus sulcatus Davis, p. 343. tern, two large foramina flank the basal tubercle, whereas two to 1891 Ctenacanthus sulcatus Woodward, p. 101. three small foramina are present on the tubercle itself. 1982 Amelacanthus sulcatus Maisey, pp. 8–10, fig. 5A–E.

Enameloid microstructure. The enameloid is made up of a Material. Samples AO40, AO55, AO47bis, AO50, Khuff Forma- homogeneous layer of single crystallites (SCE), which covers the tion, yielded 25 fragments. Specimen used for imaging: entire crown surface. The crystallites are rod-shaped, long (up to MPUM10907; remaining specimens: MPUM10908 (11), 1 lm) and randomly orientated. MPUM10925 (3), MPUM10943 (9), MPUM10953 (1). 330 PALAEONTOLOGY, VOLUME 56

MPUM11058 from another level of the Khuff Formation in the 1982). A. laevis and A. pustulatus can be rejected, respec- Haushi-Huqf area was imaged for additional observations. tively, based on the absence of posterior marginal denti- cles and the upward direction of the same denticles. Description. Slightly posteriorly recurved and laterally flattened Instead, a closer affinity with A. sulcatus is assumed based spine of considerable length (largest fragment approximately on the spines being twice as deep as broad, the lateral 30 mm in length and 10 mm in antero-posterior dimension) faces diverging at about 30 degrees and the presence of with pointed apex. Ornamented with ten or more coarse longi- roughly 15 costae per side, whereas the spines of A. plica- tudinal enameloid costae per flank, which run parallel and along most of the length of the spine. They may be more narrowly tus are shaped like an equilateral triangle and possess a spaced near the posterior edge, and the apex appears smooth. larger number of costae. However, a definitive conclusion The anterior margin is acute, but rounded and not characterized is not possible due to the fragmentary nature of the mate- by a distinct enameloid rib. The posterior wall is concave with rial. flattened centre and a low rise mesially, as well as well-developed downward pointing denticles (‘hooks’) at about equal height on both margins, which continue up to the very apex. The central Subclass EUCHONDROCEPHALI Lund and Grogan, 1997 cavity is of a large flattened oval shape and displaced posteriorly. Order EUGENEODONTIFORMES? Zangerl, 1981

Remarks. The affinities of the type of spine described here Gen. et sp. indet. are complex, and many phalacanthous shark genera show Figure 11A–D features reflected in this material. However, a hybodonti- form relationship can be discounted, based on descrip- Material. Sample 965-2, Khuff Formation, yielded two broken tions by Maisey (1978), as well as any relation to the specimens. Specimen used for SEM imaging: UC20272; remain- Symmoriiformes or the Ctenacanthiformes, based on fea- ing specimen: UC20310. tures described by Ginter et al. (2010) and Maisey (1982), respectively. The shared characters between our material Description. These specimens are seemingly crown fragments and Amelacanthus Maisey, 1982, include, most impor- belonging to much larger teeth than any other teeth recovered tantly, broad, smooth costae covered by a shiny, thick in the fauna. The largest fragment (imaged) measures 1.9– outer enameloid layer and separated by narrow intercostal 2.0 mm mesio-distally, 0.8–1.0 mm labio-lingually and 1.0 mm grooves. Other diagnostic features recognized in the Khuff high. The remains each show a very rounded cusp apex and a rounded longitudinal crest. From this crest, strong wavy cristae material include spines slender and slightly recurved; run down from the cusp on both the labial and lingual sides, anterior margin acute but rounded; subtriangular outline but from the crest they descend in a straight manner and in in section; posterior wall concave or flat, sometimes with pairs, with each crista being on opposite sides. These cristae a low rise mesially; distinct anterior rib may be absent; develop into large labially and lingually extending lobes around posterolateral margins ornamented apically by small, usu- what may be the main cusp. ally downcurved and rounded or pointed denticles (Mai- sey 1982). The thick enameloid layer and the concave Remarks. The surface ornamentation observed on these posterior wall suggest a neoselachian relationship for the crown fragments is reminiscent of the strong relief often genus, and the gross morphology of Amelacanthus is simi- observed in both the Eugeneodontiformes and the Or- lar in some respects to Nemacanthus (Maisey 1982). Four odontiformes. Ginter et al. (2010) caution that distin- species are assigned to Amelacanthus: A. sulcatus (Agassiz, guishing between isolated orodont and eugeneodont teeth 1837), A. plicatus (Agassiz, 1837), A. laevis (Davis, 1883) is very difficult and often remains arbitrary, which is why and A. pustulatus (Davis, 1883), which are distinguished an absolute distinction is not attempted here, based on mainly based on the number and breadth of the costae such limited material. A eugeneodontiform relationship is and the diverging angle of the lateral flanks (Maisey used here, merely based on the stratigraphical range of

FIG. 11. Eugeneodontiform tooth fragments and dermal denticles from the Khuff Formation, Haushi-Huqf area, central eastern Oman. A–D, Eugeneodontiformes gen. et sp. indet. UC20272, loc 6–7, sample 965-2, Haushi Cliff; tooth fragment. A, lingual ⁄ labial, B, lingual ⁄ labial, C, apical, and D, lateral views. E–W, Dermal denticles. E–F, morphotype 1, loc 6–7, sample 965-4, Haushi Cliff. E, lateral, and F, posterior views. G–H, morphotype 2, loc 6–7, sample 965-4, Haushi Cliff. G, apical, and H, lateral views. I–K, morphotype 3, MPUM10944, loc K4, sample AO50, Haushi Cliff. I, anterior, J, apical, and K, lateral views. L–M, morphotype 4, loc 6–7, sample 965-4, Haushi Cliff. L, apical, and M, lateral views. N–O, morphotype 5, loc 6–7, sample 965-2, Haushi Cliff. N, apical, and O, lateral views. P–Q, morphotype 6, loc 6–7, sample 965-2, Haushi Cliff. P, apical, and Q, lateral views. R–S, morphotype 7, loc 6–7, sample 965-2, Haushi Cliff. R, apical, and S, lateral views. T–U, morphotype 8, loc 6–7, sample 965-2, Haushi Cliff. T, apical, and U, lateral views. V–W, morphotype 9, UC20377, loc 6–2, sample 965-9, Saiwan. V, apical, and W, lateral views. Scale bars represent A–D, 500 lm; E–F, 300 lm; G–H, 200 lm; I–K, 300 lm; L–U, 200 lm; V–W, 300 lm. KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 331

A B

C D

H

E F G

K

I J

M O L N

Q

S

P R

T U

V W 332 PALAEONTOLOGY, VOLUME 56 the order extending beyond the Carboniferous into the arranged (Ginter et al. 2010). The only Permian record of Triassic, whereas the range of the Orodontiformes is cur- the genus is from the Cisuralian of Kansas, USA (Ewell rently limited to the Carboniferous (Ginter et al. 2010). and Everhart 2005, as Chomodus), although Ivanov (2000) stated that Permopetalodus frederixi Kozlov, 2000, from the Artinskian of the Ural Mountains of Russia is similar Order PETALODONTIFORMES? Zangerl, 1981 to some tooth variations of Chomatodus. Due to extreme confusion in the taxonomical organization of the genus, Gen. et sp. indet. no further identification is attempted here. Figure 9K–O

Material. Sample AO214, Khuff Formation, yielded two broken Superorder HOLOCEPHALI Bonaparte, 1832–1841 specimens. Specimen used for SEM imaging: MPUM11053; Order COCHLIODONTIFORMES Obruchev, 1953 remaining specimen: MPUM11054. Family COCHLIODONTIDAE Owen, 1867

Description. Large cusped, platform-shaped teeth (largest frag- Genus DELTODUS Morris and Roberts, 1862 ment is maximally 1.9 mm labio-lingually and 1.7 mm high). In apical view, the lateral extremity is well rounded and the labial Type species. Poecilodus sublaevis Agassiz, 1838; from the Vise´an margin is straight, whereas the lingual margin is somewhat con- (Mississippian) of Armagh, Ireland. vex. Both the base and the largest part of the crown are extre- mely flattened and are separated by a deeply incised crown–base junction. The crown protrudes beyond the base along the entire Deltodus aff. mercurei Newberry, 1876 circumference. An acute circumferential rim is present at the Figure 9P–S crown shoulder, as well as a well-raised ridge of variable height on the apical surface, which is only slightly set back from the 1876 Deltodus mercurei Newberry, p. 137, pl. 3, figs 1–1a. outer lingual margin. A sinuous row of cusps that become 1883 Deltodus mercurii St. John and Worthen, pl. 10, increasingly asymmetrical towards the central part of the tooth fig. 2a–d. is positioned on the labial part of the crown. At least seven lat- 1883 Deltodus powelli St. John and Worthen, pp. 154–156, eral cusplets are recognized on one extremity before what might pl. 9, figs 1a–f. be the main cusp. The crown surface is irregular with cristae of 1883 Deltodus propinquus St. John and Worthen, variable strength in mostly labio-lingual orientation, connecting pp. 156–158, pl. 10, figs 4a–e (not figs 3a–e). the outer rims with the cusplets, but also discontinuous cristae 1916 Deltodus mercurii Branson, pp. 648–652, pl. 5, in mesio-distal orientation can be observed. figs 1–11; pl. 2, figs 27–28; pl. 6, figs 1–6. The base is roughly rectangular in outline, and the basal face 1943 Deltodus mercurii Hussakof, p. 1834. is smooth and flat to slightly concave. It is tilted lingually, so 1982 Deltodus mercurii McKee, pp. 121–122. the labial margin reaches furthest downward. A dense row of 1982 Deltodus sp. McKee, p. 488. foramina of variable size is present both lingually and labially, but the foramina may appear horizontally flattened on the lin- Material. Samples AO40, AO55, Khuff Formation, yielded 24 gual side. complete and broken specimens. Specimens used for SEM imag- ing: MPUM10912, MPUM10913; remaining specimens: Remarks. The tentative assignment of this material to the MPUM10903 (1), MPUM10923 (21). Petalodontiformes is based on a number of characteristic features of the group as described in Ginter et al. (2010): Description. Dentition consisting of large convoluted tooth plates the crown base is commonly bordered by a sometimes (7 mm mesio-distally, 8 mm labio-lingually, but fragments indi- imbricated ridge that may be more prominent lingually; a cate that dimensions up to 12 mm are possible). The plates have cutting edge that may consist of a series of large triangu- a prominent convex ridge on the apical surface along the radial lar lobate ‘cusps’ and basolingual projection of the base axis, which gradually grows larger across the plate and is broad- paired with deep incision of the crown–base junction, est at the lingual margin, causing it to appear spatulate in out- although our material displays basolabial projection of line. The broad, rounded end is directed inwards. The crown is the base. The retracted nature of the base underneath the thickest at the ridge and flattened posteriorly by a furrow, after crown is also believed to be characteristic. The material which a thinner distal wing expands, which creates the deltoid shape of the tooth plate. The edge of the wing may curl upward further displays some similarities to Chomatodus Agassiz, slightly, especially at the labial corner. The labial border meets 1838, which is normally characterized by a very low the lingual at an obtuse angle. A series of subtle but clear trans- crown, transverse elongation of the teeth and by the gen- verse ridges that run parallel to the lingual margin are arranged eral presence of imbricated basal ridges. The base of Cho- in a radially stepwise manner, which creates the appearance of matodus is short, of rectangular outline and possesses overlapping segments with the lingual segments overlying the multiple slit-like foramina, but these are vertically labial ones. The ridges spread across the ridge and onto the dis- KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 333 tal wing. The entire crown surface is perforated by small and gually). The shorter lingual margin is straight or slightly con- randomly located pores, but these may be worn. The basal face cave, whereas the labial margin is straight to slightly oblique at is smooth, concave and conforms to the contour of the crown. the lateral extremities, but strongly concave centrally. In lateral aspect, the plates are arched labio-lingually and the mesial and Remarks. Inclusion within the Cochliodontiformes is distal margins are turned up, causing the crown surface to be based on the accommodation within the order of tooth convex labio-lingually and concave (either gently sloping or with plates with a punctate or smooth and ridged or grooved two distinct bends) mesio-distally. The base of the plates is com- crown surface. Furthermore, the Cochliodontidae include posed of lamellar tissue, and the basal face is smooth. It follows the contours of the plate, save for a U-shaped depression in the moderately to strongly arched and spiralled plates, which central labial part, reaching across two-thirds of the labio-lingual also agrees with the material described here. The charac- dimension of the plate and opening onto the labial margin. The teristics match those described as typical for the genus crown surface is covered by radially stepwise deposited hard tis- Deltodus, including most importantly the deltoid shape of sue with the labial segments overlapping the lingual ones. A ser- the plates due to the development of the distal wing, but ies of transverse ridges is created by the overlapping segments, also the spatulate convex ridge with directed inward broad composed of white, hypermineralized dentine, whereas the hard end, the labial edge curling upwards and the weak ridges tissue in between is grey. In worn tooth plates, only the ridges traversing the crown surface (Stahl 1999). All currently remain, albeit lower and smoother. known Deltodus species are from the Carboniferous, except for D. mercurei Newberry, 1876, which is known Remarks. The assignment of the described specimens to from the lower Permian Phosphoria (Embar) Formation Solenodus Trautschold, 1874, is based on the shape and in Wyoming, USA (Branson 1916; see also Stahl 1999); arching of the plates, as well as the texture of the crown from the earliest Cisuralian Pakoon Formation, Iceberg surface. The taxonomic association of this genus to the Canyon, Nevada (as Deltodus sp., McKee 1982) and from Cochliodontiformes is tentative and listed as incertae se- the Kaibab Formation in the Grand Canyon, Arizona, dis, because of prolonged disagreement. Lebedev (1994, in USA (Hussakof 1943), which is of late Cisuralian or earli- pers. comm. with Stahl 1999) is convinced of the cochli- est Guadalupian age. Direct assignment of the Khuff mate- odontiform relationship, based on the recovery of asym- rial to D. mercurei based on morphological characters is metrical plates referable to Solenodus. Because the not possible due to the more acute deltoid apical outline Cochliodontiformes accommodate tooth plates with a and the transverse undulations rather than straight ridges punctate or smooth and ridged or grooved crown surface in the latter species. The material available is not deemed (Stahl 1999) and because these specimens are recovered sufficiently well preserved (fragmented) to obtain a reliable in association with another cochliodontiform, Deltodus set of diagnostic characters. Nevertheless, this material Morris and Roberts, 1862, the taxonomic position accord- represents the youngest record of Deltodus globally. ing to Lebedev (1994, in Stahl 1999) is followed here. The specimens from the Khuff fauna are assigned to the only species referred to the genus, S. crenulatus Trautschold, Family INCERTAE SEDIS 1874, with some reservations, because of a stronger angle between the mesial and distal margins, slight differences Genus SOLENODUS Trautschold, 1874 in the outline of the lingual and labial margins and a smaller size overall. Type species. Solenodus crenulatus Trautschold, 1874; from the Pennsylvanian at Mjatschkowa in the Moscow region, Russia. Additional Material Dermal denticles Solenodus cf. crenulatus Trautschold, 1874 Figure 11E–W Figures 9T–W, 10L–M Remarks. A large number of dermal denticles (also 1874 Solenodus crenulatus Trautschold, p. 293, pl. 28, fig. 11. referred to as menaspoid scales in Angiolini et al. 2003a) have been recovered from both collections. In the MPUM Material. Samples AO55, AO214, Khuff Formation, yielded four collection, the relevant lot numbers are MPUM10904, complete and broken specimens. Specimen used for light micro- MPUM10924, MPUM10942 and MPUM10952. Establish- scope and SEM imaging: MPUM11052; remaining specimens: ing their precise affinity with particular taxa is problem- MPUM11032 (3). atic, because they were never found in direct association with teeth, but always as isolated elements. However, both Description. Large and bilaterally symmetrical tooth plates of ctenacanth and hybodont teeth have been recovered in spatulate rectangular shape in apical aspect (4.2 mm (labial part) and 2.3 mm (lingual part) mesio-distally; 4.0 mm labio-lin- the fauna and this is reflected in the dermal denticle 334 PALAEONTOLOGY, VOLUME 56 assemblage. Nine morphotypes are recognized (Table 1). addition to that, however, because of the primitive attach- Ctenacanth denticles are of compound morphology (Reif ment of the base to the crown and the less porous vascu- 1978; Williams 1998; Ginter 2002), whereas hybodontid larization system, which is in contrast to the basal denticles have a generally rounded base with a flat or features of the well-known hybodontoids that arose dur- convex basal face and a weakly developed neck (Reif ing the Triassic, it is considered that the hybodonts from 1978; Thies 1995). Morphotype 7 is identified tentatively Oman should be attributed to the stem Hybodontiformes, as a symmoriiform dental element, based on similarities that is, Hybodontiformes excluding the Hybodontoidea. observed with a median(?) symmetrical element of Steth- acanthus altonensis (St. John and Worthen, 1875) from the Mississippian, described and figured in Lebedev Taphonomy and palaeoecology of the Khuff Formation (1996; fig. 5A). fauna

The Wordian Khuff Formation fauna is well established, DISCUSSION with a total of 15 chondrichthyan genera containing 19 species recorded from the MPUM and UC sample collec- Systematic considerations – Hybodontiformes tions (Figs 3 and 12). The material is abundant, diverse, and even though fragmentation occurs due to the fragility Coates and Gess (2007, p. 1441) stated that ‘isolated teeth of the material, a large number of specimens are in pris- are standard alternatives to articulated remains as markers tine condition. There is no evidence that any specimens for temporal, palaeoecological and biogeographical taxon- have been reworked from significantly older strata, and range estimates’. They suggested that these teeth, includ- the differences in colour recorded by specimens within ing more deviant morphologies (such as those described the same sample are attributed to factors such as fungal in Rees and Underwood 2002 and listed in Fischer 2008), or bacterial activity and the degree and timing of permin- may be useful as an ichthyolithic signal of hybodontiform eralization, rather than differences in thermal alteration distribution, and it is believed that this study makes an (cf. Tway et al. 1986). The recovered teeth are small, usu- important contribution. Based on jaws, braincase and ally not exceeding a few millimetres in size. An ontoge- postcranial skeletal features, the split between the Hyb- netic bias is rejected, because if these teeth did stem from odontiformes and Neoselachii has been placed tentatively juveniles, a larger proportion of cusped teeth would be in the late Devonian (Coates and Gess 2007). In turn, the expected rather than the crushing dentitions that are minimum base of the stratigraphic range of the Hyb- common in this fauna. Instead, the small size and abun- odontiformes as a monophyletic order has been estab- dance of the material is interpreted as being the result of lished as Vise´an (Mississippian) in age, based on depositional processes. The four largest samples are inter- Onychoselache Dick, 1978 (Coates and Gess 2007), and preted as storm-winnowed tempestites, where shallow- the earliest node date of the Hybodontoidea is Kasimo- water debris was transported basinward and redeposited vian–Gzhelian (Pennsylvanian) in age, based on Hamilto- according to settling velocity, resulting in a size-selected, nichthys Maisey, 1989 (Maisey 1989). The next series of concentrated assemblage (cf. Dattilo et al. 2008). branching events spans the Permian–Triassic boundary As the relative stratigraphic positions of the MPUM (although this may be an artefact of fossil record incom- collection samples are better known than those of the pleteness; Coates and Gess 2007), which means that the UC collection, the remaining discussion mostly focuses hybodont genera described from the Guadalupian in this on the MPUM data (Fig. 3). The collection illustrates study are well positioned within the Hybodontiformes. In the importance of sample size, because the small samples

TABLE 1. Recovery information and interpretation of denticles per morphotype (MPUM collection).

Morpho type AO40 AO55 AO47bis AO50 Interpretation Figure

1 ··· ·Ctenacanth Figure 11E–F 2 ··· ·Hybodont Figure 11G–H 3 · Indet. Figure 11I–K 4 ··· ·Hybodont Figure 11L–M 5 ···Hybodont Figure 11N–O 6 ··· ·Hybodont Figure 11P–Q 7 ··Symmoriiform? Figure 11R–S 8 ··· ·Hybodont Figure 11T–U 9 · Hybodont Figure 11V–W KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 335

finer-grained beds, shows that all these samples are hyb- odont dominated, preventing any definite conclusions at this stage. There are also currently no clear indications of more frequent hybodont domination in Member 3 compared to Member 2, in accordance with depositional setting of the basin. In terms of relative diversity, based on the number of genera assigned to each group, the hybodontiforms dominate each of the large samples (Fig. 13C–D). The euchondrocephalians are represented by the fewest number of specimens and have the lowest generic diversity (Fig. 13). They were only rarely present in the smaller (3–5 kg) samples (Fig. 3). By using the complete suite of samples, the ranges of the most common taxa within the Khuff Formation can be determined. Both ctenacanthiforms and hybodonti- forms are recorded from the base of Unit D of Member 1 through to the uppermost part of Member 3 (Fig. 3). Ctenacanthiforms range even further downward, because they are also recorded from the Sakmarian Saiwan For- mation at Jabal Gharif, and in addition, a slightly older FIG. 12. Stratigraphic elasmobranch occurrence data per taxon and range information (UC collection). No stratigraphic occurrence in the region is suggested by the recovery of order is implied in the representation of the sections. cladodont teeth from the basalmost bed (60 cm) of the Saiwan Formation in the Saiwan area (upper Sakmarian, Cisuralian; Angiolini et al. 2003b). (3–5 kg) record a maximum of ten genera per individual Considering the Hybodontiformes in the traditional sample (sample AO214, responsible for this maximum, sense, their isolated teeth occur abundantly in upper Palae- is an unusually rich sample compared with the remain- ozoic and Mesozoic rocks (Rees and Underwood 2002) ing small samples, which normally reach a maximum of and provide evidence that the hybodonts were one of the 6–7 genera) but an average richness of three, whereas most successful chondrichthyan lineages (Rees 2008). The the four large (10–15 kg) samples yield a maximum of Wordian Khuff fauna, as well as a Cisuralian fauna from nine genera and an average of eight. Furthermore, due Texas described by Johnson (1981), show that hybodonts to these differences in sample size and clear evidence were a well-established element of marine shark faunas that smaller samples normally record fewer taxa, only throughout the Permian and were the dominant taxon in the four largest samples from the MPUM collection have certain areas. A potential clue to their success is that the been analysed palaeoecologically (Fig. 3; Supporting variety of tooth shapes found in hybodont families (Rees information). When pooled together, these four samples 2008) indicates the utilization of a number of different are dominated by ctenacanthiform and hybodontiform food sources. As discussed in the systematic section of this taxa, in almost equal relative abundance when assessed study, however, the Palaeozoic forms may represent a stem by numbers of specimens (Fig. 13A). Individual samples, group of their Mesozoic counterparts (i.e. Hybodontifor- however, are dominated by either ctenacanthiforms or mes excluding the Hybodontoidea). Most revisions to the hybodontiforms (Fig. 13B). Samples dominated by the Hybodontiformes have until now focused on the Mesozoic latter group are coarser grained (Fig. 3), which suggests taxa (e.g. Hybodus, ‘Polyacrodus’), and new genera have a possible taphonomic bias. Alternatively, if grain size been erected to reflect current taxonomic views. The Palae- reflects depositional setting, then the differences may be ozoic material is in need of similar review. recording real habitat preferences: the highly cusped The composition of the Khuff fauna is comparable to teeth of ctenacanthiforms such as Glikmanius indicate a the hybodont-dominated Guadalupian–Lopingian shark more pelagic lifestyle and so might be expected to be assemblages of the Ural Mountains, as reviewed by Ivanov more common in distal, finer-grained lithologies, (2005), and also strengthens his proposal of a late Palaeo- whereas the crushing dentitions of hybodontiforms zoic (Cisuralian) origin for synechodontiform sharks. might be expected to occur more frequently in coarser Upper Carboniferous–Guadalupian deposits in the Ural beds from more proximal depositional settings. An Mountains and other localities in arctic Russia have attempt at reassessing this potential bias using the four yielded a number of specific groups that are also (tenta- most abundant smaller samples, of which AO41 is from tively) represented in the Khuff fauna. These include the a coarse bed and AO210, AO211 and AO214 are from Symmoriiformes, with, for example, Stethacanthus from 336 PALAEONTOLOGY, VOLUME 56

A C

BD

FIG. 13. Relative abundances of chondrichthyan groups from the Wordian Khuff Formation (based on MPUM collection). A, Overall relative abundance of major groups using numbers of specimens. B, Relative abundance of major groups per sample using numbers of specimens. C, Overall relative abundance of major groups using numbers of genera. D, Relative abundance of major groups per sample using numbers of genera. Samples in B and D are ordered stratigraphically (Fig. 3). the Asselian (Ivanov 1999) and from the Wordian–Capit- Middle Phosphoria Formation, Wyoming, USA, which anian (Minikh 1999; referred by A. Ivanov, pers. comm. contains Glikmanius occidentalis and other ctenacanthi- 2012); the Ctenacanthiformes, with Heslerodus from the forms, Arctacanthus and euchondrocephalians (eugen- Gzhelian–Asselian boundary (Ivanov 1999) and Glikma- eodontiforms and a petalodontiform; Branson 1933). nius from the Artinskian (Kozlov 2000) and from the Ivanov et al. (2007, 2011) mentioned the presence of Wordian–Capitanian (Minikh and Minikh 1996, Malysh- Guadalupian phoebodontiforms, symmoriiforms and Coo- eva et al. 2000; all referred to Glikmanius by Ivanov 2000 leyella Gunnell, 1933, as well as ctenacanth, hybodont and and Ginter et al. 2005); the Anachronistidae, with Cooley- neoselachian dermal denticles, in the Guadalupe and ella from the Sakmarian–Artinskian and Roadian (Ivanov Apache Mountains of western Texas. Xenacanthids are 2000, 2011), and rare Petalodontiformes such as Permop- common in assemblages of western Europe and North etalodus from the Artinskian (Kozlov 2000). Composi- America (Ivanov 2005), such as the very rich upper tional similarities further exist with the Guadalupian Pennsylvanian fauna from Nebraska, USA, studied by chondrichthyan faunas from the Akasaka Formation at Ossian (1974), which contains Glikmanius myachkovensis Akasaka, Japan, which contains Glikmanius occidentalis, (Lebedev, 2001; Ginter et al. 2005) and other ctenacanths, indeterminate cladodont teeth and ‘Lissodus’ sp. (Yamagi- xenacanths, protacrodonts, hybodonts, as well as euchon- shi and Fujimoto 2011), and from the Pustula Member, drocephalans such as orodontiforms, eugeneodontiforms, KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 337 petalodontiforms and holocephalans such as Deltodus provisional until the teeth described in this study are Morris and Roberts, 1862. It therefore also has many ele- definitively assigned to the genus. Palaeogeographically, ments in common with the Wordian fauna from Oman, this study represents the first record from the western but the Khuff fauna lacks xenacanthids, although their fringe of Neotethys for all taxa. Cooleyella is the only presence has been recorded from the underlying Cisura- genus with a previous record from the Southern Hemi- lian (Artinskian) Gharif Formation in the same location sphere (Gondwanan) part of Pangaea, that is, from Brazil, in Oman (Schultze et al. 2008), which shows more fresh- a location that has also yielded Carboniferous and Cisura- water influence (Fig. 1). From Wuchiapingian deposits, lian (Artinskian) Sphenacanthus fin spines (Chahud et al. exposed in the Abadeh-Shahreza belt in south-western 2010), and its occurrence in Oman shows that Cooleyella Iran, a fragmentary petalodontiform tooth (Golshani and was present in almost all major provinces and that the Janvier 1974) assigned to Megactenopetalus (Ossian 1976; genus approached global distribution. Hansen 1978) and a polyacrodontid(?) tooth similar to Stratigraphically, this study represents the first record ‘Polyacrodus’ lapalomensis Johnson, 1981 (Hampe et al. from the Wordian for all taxa, although Glikmanius was 2011) have been reported, drawing general parallels with already known from this age by means of G. occidentalis. the Khuff fauna. The Iranian deposits are representative All but one of the previously described taxa are restricted of the northern (outer) shelf of the Neotethys and there- to the Palaeozoic, and except for Cooleyella, their occur- fore stem from the same palaeogeographic area as the rence in the Wordian Khuff fauna represents their youn- Khuff Formation. gest record (Table 2; Fig. 14). Only Nemacanthus was previously restricted to the Mesozoic, and its identifica- tion here entails a downward range extension leading to Stratigraphic and palaeogeographic implications its oldest occurrence and the only record from the Palae- ozoic so far. Although the presence of Permian sharks in Oman was mentioned previously in the literature (Tintori 1998; An- giolini et al. 2003a; Schultze et al. 2008), this study repre- The Permian fossil record and extinction of sharks sents the first detailed faunal description, and the occurrence of this fauna in the Wordian Khuff Formation The unusually large number of new taxa in the Khuff requires adjustments to the stratigraphic ranges and fauna may be explained by the small size of the remains geographical distributions of the previously described taxa and the fact that Permian fossil sharks of this region have that have been recognized (Table 2). The suggested not been studied in detail before. That a newly sampled adjustments to ‘Palaeozoic Genus 1’ should remain location should yield numerous new taxa is a reflection of

TABLE 2. Global records of pre-existing taxa recognized in the Khuff fauna.

Taxon Age Location Remains References

Glikmanius Pennsylvanian (Carboniferous) – USA, Russia, Teeth Ginter et al. (2005, 2010) Wordian (Guadalupian, Permian) Ukraine, Japan and Lebedev (2001) G. myachkovensis Pennsylvanian (Carboniferous) USA, Russia, Ukraine Teeth Ginter et al. (2005, 2010) Reesodus gen. nov. Mississippian (Carboniferous) England, Russia Teeth Rees and Underwood (2002; as ‘Paleozoic Genus 2’) ‘Paleozoic Genus 1’ Pennsylvanian (Carboniferous) – Spain, Germany, USA Teeth Rees and Underwood (2002) Cisuralian (Permian) Gunnellodus Mississippian – USA, Russia ‘Teeth’ Hoffman and Hageman (2011) Pennsylvanian (Carboniferous) Cooleyella Vise´an (Mississippian, Carboniferous) – England, Belgium, Teeth Ivanov (2011) Capitanian (Guadalupian, Permian) Brazil, USA, Russia C. fordi Vise´an (Mississippian, Carboniferous) – England, Belgium, Russia Teeth Ivanov (2011) Artinskian (Cisuralian, Permian) Nemacanthus Lower Triassic – Rhaetian (Upper Triassic) England, Greenland, Fin spines Cappetta (1987) Spitsbergen, USA Amelacanthus Mississippian (Carboniferous) UK Fin spines Maisey (1982) Deltodus Tournaisian (Carboniferous) – UK, Belgium, Teeth Stahl (1999) Cisuralian (Permian) France, Russia, USA, Thailand Solenodus Pennsylvanian (Carboniferous) Russia Teeth Stahl (1999) 338 PALAEONTOLOGY, VOLUME 56

also the most diverse fauna known from the entire Permian. The Khuff fauna significantly enhances the Guadalupian fossil record of chondrichthyans and also changes our under- standing of their diversity prior to the extinction events of the late Guadalupian and late Changhsingian. The upward range extensions of six chondrichthyan genera into the upper Wordian demonstrates that extinction of these Palaeozoic taxa was not a gradual process spanning c. 50 million years from the end of the Mississippian to the end of the Cisura- lian, but must have been much more abrupt. Whether their ultimate extinction can be tied directly to either of the major biotic crises of the Permian remains to be determined and requires further improvements in our understanding of Guadalupian and Lopingian shark faunas worldwide. The upward range extensions also imply more gaps in the Penn- sylvanian, Cisuralian and lower Guadalupian fossil record of sharks than has hitherto been appreciated. Finally, the occur- rence of Nemacanthus in the Khuff fauna demonstrates for the first time that this genus, at least, survived both major extinction events of the Permian.

FIG. 14. Stratigraphic ranges of all genera recovered in the Khuff fauna from the upper Wordian. Light grey indicates CONCLUSION extensions to the established range (based on data in Table 2). The Khuff Formation of the Haushi-Huqf area of Oman yields abundant and well-preserved chondrichthyan the general patchiness of the fossil record and, moreover, remains, recording the most diverse Wordian assemblage an excellent indication that both the region and known with a total of 15 chondrichthyan genera containing stratigraphic interval in question have been poorly sam- 19 species. The hybodontiforms are the most diverse group. pled (cf. Tarver et al. 2007). This is corroborated by a Individual samples are dominated by either hybodonti- series of closely spaced phylogenetic branching events forms or ctenacanthiforms, with lower abundances of euse- spanning the Permian–Triassic boundary, indicative of lachians and neoselachians. Euchondrocephalians appear to record incompleteness (Coates and Gess 2007), and fur- have only had a minor share in the community. The most ther correlates with a similar gap in the availability of common groups range throughout the formation, and the sedimentary formations in at least the North American ctenacanthiforms have been shown to already be present in late Palaeozoic geological record (Peters 2006). These upper Sakmarian deposits in the Haushi-Huqf area. observations support the hypothesis of Twitchett (2001) This study represents the first detailed faunal descrip- that a relatively poor chondrichthyan fossil record in the tion of Permian sharks from Oman and includes an Guadalupian and Lopingian is masking the true diversity unusually large number of new taxa. Palaeogeographically, of shark faunas at that time, leading to inaccurate views it represents the first record from the western margin of on extinction patterns among sharks. Indeed, there are Neotethys for all described taxa. The assemblage records relatively few published studies of Guadalupian and Lo- the oldest occurrence of Nemacanthus and the only record pingian chondrichthyan faunas. The Palaeobiology Data- from the Palaeozoic so far. It records the youngest occur- base (http://paleodb.org, accessed December 2011), for rence of almost all other previously described taxa, except example, records 57 Cisuralian collections, but only 21 Glikmanius and Cooleyella, which were already known Guadalupian collections and 27 Lopingian collections. from the Wordian and Capitanian, respectively. The average richness of these Permian localities is only 1– These results highlight the patchiness and relatively 2 genera, with a maximum of five genera recorded in the poor sampling of the Guadalupian shark fossil record. most diverse Cisuralian collection (Ivanov 2005), eight in The upward extension of the stratigraphic ranges of many the Guadalupian (Branson 1933) and four in the taxa indicates that extinction of these taxa must have Lopingian (Wang et al. 2007). With a total of 15 genera been more abrupt than hitherto supposed. The Khuff recognized, the Khuff fauna is not only the most diverse fauna significantly enhances the Guadalupian chondri- Guadalupian chondrichthyan fauna recorded to date, it is chthyan fossil record and also changes our understanding KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 339 of chondrichthyan biodiversity patterns prior to the REFERENCES major mass extinction events of the Permian. AGASSIZ, L. 1833–1843. Recherches sur les poissons fossiles,5 Acknowledgements. We would like to thank the following people, Vols. Imprimerie de Petitpierre, Neuchaˆtel, 1420 pp. who made this study possible: Prof. L. Angiolini (University of ANGIOLINI, L. and BUCHER, H. 1999. Taxonomy and Milan, Italy) for practical assistance and stratigraphic and local- quantitative biochronology of Guadalupian brachiopods from ity data; Prof. C.M. Henderson and K. Zubin-Stathopoulos the Khuff Formation, Southeastern Oman. Geobios, 32, 665– (University of Calgary, Calgary) for access to the material, geo- 699. graphical and stratigraphic information of the samples utilized —— NICORA, A., BUCHER, H., VACHARD, D., PILL- and technical assistance; Prof. M.B. Hart (Plymouth University, EVUIT, A., PLATEL, J. P., BAUD, A., BROUTIN, J., Plymouth) for technical advice and constructive comments; Dr MARCOUX, J. and AL HASHMI, H. 1998. Late Permian A. Baud (University of Lausanne, Switzerland) for stratigraphic fauna from the Khuff Formation, southeastern Oman: preli- assistance; Dr A. Ivanov (St. Petersburg State University, St. minary report. Rivista Italiana di Paleontologia e Stratigrafia, Petersburg) and Dr. A.M. Minikh (Saratov State University) for 104, 329–340. taxonomical discussion and help with obtaining Russian publica- —— BALINI, M., GARZANTI, E., NICORA, A., TIN- tions; N.D. Jacobsen (Plymouth University, Plymouth) for assis- TORI, A., CRASQUIN, S. and MUTTONI, G. 2003a. tance with picking the material; Dr C. Lombardo (University of Permian climatic and paleogeographic changes in Northern Milan, Italy) and C. Chinery (University of Calgary, Calgary) for Gondwana: the Khuff Formation of Interior Oman. Palaeoge- assistance with depositing the material; J. Adolfssen (Natural ography, Palaeoclimatology, Palaeoecology, 191, 269–300. History Museum of Denmark, Copenhagen) and P. Bond (Plym- —— —— —— —— —— 2003b. Gondwanan deglaciation and outh Electron Microscopy Centre) for help with using the SEM. opening of Neotethys: the Al Khlata and Saiwan Formations The quality of the manuscript was improved following critical of Interior Oman. Palaeogeography, Palaeoclimatology, Palaeoe- and constructive comments from R. Soler-Gijo´n (Museum fu¨r cology, 196, 99–123. Naturkunde der Humboldt Universita¨t, Berlin) and M. Ginter BENGTSON, P. 1988. Open nomenclature. Palaeontology, 31, (University of Warsaw, Warsaw). This research was funded by 223–227. personal grants to M. B. Koot from VSBfonds (Utrecht), Prins BENTON, M. J. 1998. The quality of the fossil record of verte- Bernhard Cultuurfonds (Amsterdam), Dr. Hendrik Muller Vad- brates. 269–303. In DONOVAN, S. K. and PAUL, C. R. C. erlandsch Fonds (The Hague) and Stichting Fonds Dr. Catharine (eds). The adequacy of the fossil record. Wiley, New York, 322 van Tussenbroek (Utrecht) in the Netherlands. pp. BLAKEY, R. 2009. Global paleogeography. Website: http:// jan.ucc.nau.edu/~rcb7/. Author contributions. MBK is responsible for all aspects of the BONAPARTE, C. L. J. 1832–1841. Iconografia della Fauna presented work. GC guided the study, description and systematic Italica, per le quattro classi degli animali vertebrati, 3 Vols. analysis of the material. AT obtained and processed all the sam- Dalla Tipografia Salviucci, Rome. ples and curated the material. RJT guided the postdescriptive —— 1838. Selachorum tabula analytica. Nuovi Annali della Sci- analyses of the fauna. enze Naturali, Bologna, 1, 195–214. BRANSON, E. B. 1916. The Lower Embar of Wyoming and its Editor. Adriana Lo´pez-Arbarello fauna. Journal of Geology, 24, 639–664. BRANSON, C. C. 1933. Fish fauna of the Middle Phosphoria Formation. Journal of Geology, 41, 174–183. SUPPORTING INFORMATION BURROW, C. J., HOVESTADT, D. C., HOVESTADT- EULER, M., TURNER, S. and YOUNG, G. C. 2008. New Additional Supporting Information may be found in the online information on the Devonian shark Mcmurdodus, based on version of this article: material from western Queensland, Australia. Acta Geologica Polonica, 58, 155–163. Appendix S1. List of original specimen numbers (with inte- CAPPETTA, H. 1987. Chondrichthyes II Mesozoic and Cenozoic grated sample numbers) and corresponding collection numbers Elasmobranchii, handbook of paleoichthyology, Vol. 3B. Gustav for the MPUM collection. Fischer Verlag, Stuttgart, 193 pp. Appendix S2. List of original sample numbers and specimen —— DUFFIN, C. and ZIDEK, J. 1993. Chondrichthyes. 593– numbers with corresponding collection numbers for the UC col- 609. In: BENTON, M. J. (ed.). The fossil record 2. Chapman lection. and Hall, London, 845 pp. Appendix S3. Absolute abundance (AA) and relative abun- CASIER, E. 1959. Contributions a` l’e´tude des poissons fossiles dance (RA) for specimens of all taxa in the MPUM collection. de la Belgique – XII. Se´laciens et Holoce´phales sine´muriens de Please note: Wiley-Blackwell are not responsible for the con- la province de Luxembourg. Bulletin de l’Institut Royal des Sci- tent or functionality of any supporting materials supplied by the ences Naturelles de Belgique, 35, 1–27. authors. Any queries (other than missing material) should be CHAHUD, A., FAIRCHILD, T. R. and PETRI, S. 2010. directed to the corresponding author for the article. Chondrichthyans from the base of the Irati Formation (Early 340 PALAEONTOLOGY, VOLUME 56

Permian, Para´na Basin), Sa˜o Paulo, Brazil. Gondwana EWELL, K. and EVERHART, M. J. 2005. A Paleozoic shark Research, 18, 528–537. fauna from the Council Grove Group (Lower Permian). CHEN, L., CUNY, G. and WANG, X. 2007. The chondrichth- Abstracts of the annual meeting of the Kansas Academy of Sci- yan fauna from the Middle–Late Triassic of Guanling (Guizhou ence, April 17, 2004. Transactions of the Kansas Academy of Sci- province, SW China). Historical Biology, 19, 291–300. ence, 108, 71–72. COATES, M. I. and GESS, R. W. 2007. A new reconstruction FISCHER, J. 2008. Brief synopsis of the hybodont form taxon of Onychoselache traquairi, comments on early chondrichthyan Lissodus Brough, 1935, with remarks on the environment and pectoral girdles and hybodontiform phylogeny. Palaeontology, associated fauna. Pala¨ontologie, Stratigraphie, Fazies (16), Frei- 50, 1421–1446. berger Forschungshefte, C528, 1–23. COMPAGNO, L. J. V. 1977. Phyletic relationships of living GEBHARDT, U. 1988. Taxonomie und Palo¨kologie von Lisso- sharks and rays. American Zoologist, 17, 303–322. dus lacustris n. sp. (Hybodontoidea) aus dem Stefan C (Oberkar- —— 1990. Alternative life-history styles of cartilaginous fishes in bon) der Saalesenke. Freiberger Forschungshefte, C419, 38–41. time and space. Environmental Biology of Fishes, 28, 33–75. GINTER, M. 2002. Chondrichthyan fauna of the Frasnian– COPE, E. D. 1893. On Symmorium, and the position of the Famennian boundary beds in Poland. Acta Palaeontologica Cladodont sharks. The American Naturalist, 28, 999–1001. Polonica, 47, 329–338. CUNY, G. and RISNES, S. 2005. The enameloid microstruc- —— IVANOV, A. and LEBEDEV, O. 2005. The revision of ture of the teeth of synechodontiform sharks (Chondrichthyes: ‘Cladodus’ occidentalis, a late Palaeozoic ctenacanthiform Neoselachii). PalArch, 3, 8–19. shark. Acta Palaeontologica Polonica, 50, 623–631. —— RIEPPEL, O. and SANDER, P. M. 2001. The shark —— HAMPE, O. and DUFFIN, C. 2010. Chondrichthyes fauna from the Middle Triassic (Anisian) of North-Western (Paleozoic Elasmobranchii: teeth), handbook of paleoichthyology, Nevada. Zoological Journal of the Linnean Society, 133, 285– Vol. 3D. Verlag Dr. Friedrich Pfeil, Mu¨nchen, 165 pp. 301. GLENNIE, K. W. 2005. The Geology of the Oman Mountains – DATTILO, B. F., BRETT, C. E., TSUJITA, C. J. and an outline of their origin, Second edition. Scientific Press Ltd, FAIRHURST, R. 2008. Sediment supply versus storm win- Beaconsfield, 110 pp. nowing in the development of muddy and shelly interbeds —— BOEUF, M. G. A., HUGHES CLARKE, M. W., from the Upper Ordovician of the Cincinnati region, USA. MOODY-STUART, M., PILAAR, W. F. H. and REIN- Canadian Journal of Earth Sciences, 45, 243–265. HARDT, B. M. 1974. Geology of the Oman Mountains, parts DAVIS, J. W. 1883. On the fossil fishes of the Carboniferous 1–3. Verhandelingen van het Koninklijk Nederlands Geologisch Limestone Series of Great Britain. Transactions of the Royal Mijnbouwkundig Genootschap, 31, 1–423. Society of Dublin, 1, 327–548. GLIKMAN, L. S. 1964. Sharks of the Palaeogene and their DEAN, B. 1909. Studies on fossil fishes (Sharks, Chimaeroids, stratigraphic significance. Doklady Akademii Nauk Soyuza Sov- and Arthrodires). Memoirs of the American Museum of Natural etskikh Sotsialisticheskikh Respublik, Moscow, 228 pp. (In History, 9, 211–287. Russian). DICK, J. R. F. 1978. On the Carboniferous shark Tristychius GOLSHANI, F. and JANVIER, P. 1974. Tooth fragment of a arcuatus Agassiz from Scotland. Transactions of the Royal Soci- petalodontid fish (Elasmobranchii, Bradyodonti) from the ety of Edinburgh, 70, 63–109. Permian of central Iran. Geological Survey of Iran, Report, 31, ——1998. Sphenacanthus, a Palaeozoic freshwater shark. Zoologi- 55–61. cal Journal of the Linnean Society, 122, 9–25. GUNNELL, F. H. 1933. Conodonts and fish remains from the DUFFIN, C. J. 1985. Revision of the hybodont selachian genus Cherokee, Kansas City, and Wabaunsee Groups of Missouri Lissodus Brough (1935). Palaeontographica Abteilung A, 188, and Kansas. Journal of Paleontology, 7, 261–297. 105–152. HAMPE, O., HAIRAPETIAN, V., WITZMANN, F., —— and IVANOV, A. 2008. New chondrichthyan teeth from DORKA, M. and AKBARI, A. 2011. A first fish fauna from the Carboniferous of Britain and Russia. Acta Geologica Polo- the late Permian of Baghuk Mountain, Iran. Ichthyolith Issues, nica, 58, 191–197. Special Publication, 12, 21–22. —— and WARD, D. J. 1983. Neoselachian sharks’ teeth from HANSEN, M. C. 1978. A presumed lower dentition and a the Lower Carboniferous of Britain and the Lower Permian of spine of a Permian petalodontiform chondrichthyan, Megac- the U.S.A. Palaeontology, 26, 93–110. tenopetalus kaibabanus. Journal of Paleontology, 52, 55–60. ————1993. The Early Jurassic palaeospinacid sharks of Lyme HAY, O. P. 1902. Bibliography and catalogue of the fossil ver- Regis, southern England. In HERMAN, J. and VAN tebrata of North America. Bulletin of the United States Geologi- WAES, H. (eds). Elasmobranches et Stratigraphie. Belgian cal Survey, 179, 1–868. Geological Survey, Professional Paper, 264, 53–102. HENDERSON, C. M. 2005. International correlation of the —— RICHTER, M. and NEIS, P. A. 1996. Shark remains marine Permian time scale. Permophiles, 46, 6–9. from the Late Carboniferous of the Amazon Basin, Brazil. HOFFMAN, B. L. and HAGEMAN, S. A. 2011. Shark ‘teeth’ Neues Jahrbuch fu¨r Geologie und Pala¨ontologie, Monatshefte, of the form genus Gunnellodus Wilimovsky (Idiacanthus Gun- 1996(4), 232–256. nell) represent stethacanthid denticles. Abstracts of the 143rd EVANS, H. M. 1904. A new cestraciont spine from the lower annual meeting of the Kansas Academy of Science, Baker Uni- Triassic of Idaho. Bulletin of the Department of Geology, Uni- versity, Baldwin City, Kansas, April 8–9, 2011. Transactions of versity of California, 3, 397–402. the Kansas Academy of Science, 114, 161. KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 341

HUSSAKOF, L. 1943. Permian fishes from the Kaibab Forma- KOZLOV, V. A. 2000. On the new finds of shark teeth in the tion of Arizona. Bulletin of the Geological Society of America, Artinskian deposits of the Cisuralian Region. Materials on the 54, 1834. Stratigraphy and Palaeontology of the Urals, 4, 148–153. (In HUXLEY, T. H. 1880. On the application of the laws of evolu- Russian with English abstract). tion to the arrangement of the Vertebrata, and more particu- LEBEDEV, O. A. 1996. Fish assemblages in the Tournaisian– larly of the Mammalia. Proceedings of the Zoological Society of Visean environments of the East European Platform. In London, 1880, 649–662. STROGEN, P., SOMERVILLE, I. D. and JONES, G. L. IVANOV, A. 1996. The Early Carboniferous chondrichthyans (eds). Recent advances in Lower Carboniferous geology. Geologi- of the South Urals, Russia. In STROGEN, P., SOMER- cal Society, Special Publications, London, 107, 387–415. VILLE, I. D. and JONES, G. L. (eds). Recent advances in —— 2001. Vertebrates. 196–201. In MAHLINA, M. H., Lower Carboniferous geology. Geological Society, Special Publica- ALEKSEEV, A. S., GOREVA, N. V., GORUˆ NOVA, R. tions, London, 107, 417–425. V., ISAKOVA, T. N., KOSSOVAAˆ , O. L., LAZAREV, S. —— 1999. Late Devonian – Early Permian chondrichthyans of S., LEBEDEV, O. A. and Sˇ KOLIN, A. A. (eds). Srednij kar- the Russian Arctic. Acta Geologica Polonica, 49, 267–285. bon Moskovskoj sineklizy (uˆzˇnaaˆ ˇcast’). Tom 2. Paleontologicˇes- —— 2000. Permian elasmobranchs (Chondrichthyes) of Russia. kaaˆ harakteristika. Naucˇnyj mir, Moscow, 328 pp. (In Ichthyolith Issues, Special Publication, 6, 39–42. Russian). —— 2005. Early Permian Chondrichthyans of the Middle and LEIDY, J. 1859. Descriptions of Xystracanthus arcuatus and South Urals. Revista Brasileira de Paleontologia, 8, 127–138. Cladodus occidentalis. Proceedings of the Academy of Natural —— 2011. Permian anachronistid sharks of the East European Sciences of Philadelphia, 1859,3. Platform and Urals. Palaeozoic and Mesozoic vertebrates of Eur- LUND, R. and GROGAN, E. D. 1997. Relationships of the asia: evolution, community change, taphonomy and palaeobioge- Chimaeriformes and the basal radiation of the Chondrich- ography. Proceedings of the conference dedicated to the 80th thyes. Reviews in Fish Biology and Fisheries, 7, 65–123. birthday of Vitaly IG Ochev (1931–2004), 6 December, 2011. MAISEY, J. G. 1975. The interrelationships of phalacanthous Paleontological Institute, Russian Academy of Sciences, Mos- selachians. Neues Jahrbuch fu¨r Geologie und Pala¨ontologie, cow, 17–19. (In Russian). Monatshefte, 1975, 553–567. —— NESTELL, M. and NESTELL, G. 2007. Middle Permian —— 1977. The fossil selachian fishes Palaeospinax Egerton, 1872 chondrichthyans from West Texas and relationships of the and Nemacanthus Agassiz, 1837. Zoological Journal of the Lin- Jalodontidae. Ichthyolith Issues, Special Publication, 10, 48. nean Society, 60, 259–273. —— —— —— 2011. Middle Permian fish assemblages from —— 1978. Growth and form of finspines in hybodont sharks. West Texas. Ichthyolith Issues, Special Publication, 12, 27. Palaeontology, 21, 657–666. JAN, I. U., STEPHENSON, M. H. and KHAN, F. R. 2009. —— 1982. Studies on the Paleozoic selachian genus Ctenacan- Palynostratigraphic correlation of the Sardhai Formation thus Agassiz. No. 2. Bythiacanthus St. John and Worthen, A- (Permian) of Pakistan. Review of Palaeobotany and Palynology, melacanthus, new genus, Eunemacanthus St. John and 158, 72–82. Worthen, Sphenacanthus Agassiz, and Wodnika Mu¨nster. JEPPSSON, L., ANEHUS, R. and FREDHOLM, D. 1999. American Museum Novitates, 2722, 1–24. The optimal acetate buffered acetic acid technique for extract- —— 1987. Cranial anatomy of the Lower Jurassic shark Hybodus ing phosphatic fossils. Journal of Paleontology, 73, 964–972. reticulatus (Chondrichthyes, Elasmobranchii): with comments JOHNS, M. J., BARNES, C. R. and ORCHARD, M. J. 1997. on hybodontid systematics. American Museum Novitates, 2878, Taxonomy and biostratigraphy of Middle and Late Triassic 1–39. elasmobranch ichthyoliths from Northeastern British Colum- —— 1989. Hamiltonichthys mapesi, g. & sp. nov. (Chondrich- bia. Bulletin of the Geological Survey of Canada, 502, 1–235. thyes; Elasmobranchii), from the Upper Pennsylvanian of JOHNSON, G. D. 1981. Hybodontoidei (Chondrichthyes) Kansas. American Museum Novitates, 2931, 1–42. from the Wichita-Albany Group (Early Permian) of Texas. ——2011. The braincase of the Middle Triassic shark Acronemus Journal of Vertebrate Paleontology, 1, 1–41. tuberculatus (Bassani, 1886). Palaeontology, 54, 417–428. KLUG, S. 2010. Monophyly, phylogeny and systematic position MALYSHEVA, E. O., IVANOV, A., BEZNOSOV, P. A., of the Synechodontiformes (Chondrichthyes, Neoselachii). BELYAEV, A. A. and MITYAKOV, S. N. 2000. Facies and Zoologica Scripta, 39, 37–49. ichthyofauna of the Kazanian from the Vym’ River (Komi —— and KRIWET, J. 2008. A new basal galeomorph shark Republic, Russia). Ichthyolith Issues, Special Publication, 6, 59– (Synechodontiformes, Neoselachii) from the Early Jurassic of 63. Europe. Naturwissenschaften, 95, 443–448. MCKEE, E. D. 1982. The Supai Group of Grand Canyon. Uni- KOEHRER, B., ZELLER, M., AIGNER, T., POEPPELRE- ted States Geological Survey, Professional Paper, 1173, 1–504. ITER, M., MILROY, P., FORKE, H. and AL-KIND, S. MEI, S. and HENDERSON, C. M. 2001. Evolution of Perm- 2010. Facies and stratigraphic framework of a Khuff outcrop ian conodont provincialism and its significance in global equivalent: Saiq and Mahil formations, Al Jabal al-Akhdar, correlation and paleoclimate implication. Palaeogeography, Sultanate of Oman. GeoArabia, 15, 91–156. Palaeoclimatology, Palaeoecology, 170, 237–260. KOTLYAR, G. V. and PRONINA, G. P. 1995. Murgabian MINIKH, A. V. 1999. New shark species of the Ctenacanthus and Midian stages of the Tethyan realm. Permophiles: Newslet- Ag. genus from the Kazanian stage of the Upper Permian; the ter of the Subcommission on Permian Stratigraphy, 27, 23–26. basin of the Pinega river. Transactions of the Scientific Research 342 PALAEONTOLOGY, VOLUME 56

Geological Institute of the N.G. Chernyshevskii Saratov State REGAN, C. T. 1906. A classification of the selachian fishes. University, New Series, 1, 133–138. (In Russian with English Proceedings of the Zoological Society of London, 1906, 722–758. abstract). REIF, W.-E. 1978. Types of morphogenesis of the dermal skele- —— and MINIKH, M. G. 1996. Fishes. 258–269. In ESAUL- ton in fossil sharks. Pala¨ontologische Zeitschrift, 52, 110–128. OVA, N. K. and LOZOVSKIY, V. R. (eds). Stratotipy i RICHOZ, S., BAUD, A., BE´ CHENNEC, F., CORDEY, F., opornye razrezy verhney permi povolzhya i prikamya. Kazanskiy MAURY, R., KRYSTYN, L., TWITCHETT, R. J. and Gosudarstvennyj Universitet, Kazan. (In Russian). MARCOUX, J. 2005. Permo–Triassic deposits of the Oman MORRIS, J. and ROBERTS, G. E. 1862. On the Carbonifer- Mountains: from basin and slope to the shallow platform – ous limestone of Oreton and Farlow, Clee Hills, Shropshire. Post-conference excursion no. A13 in the Oman Mountains, Quarterly Journal of the Geological Society of London, 18, 94– January 14–17, 2005. International Association of Sedimentol- 106. ogy, 24th Regional Meeting, January 10–13, 2005. Muscat, MUTTER, R. J. and NEUMAN, A. G. 2008. New eugene- Oman. odontid sharks from the Lower Triassic Sulphur Mountain RIEPPEL, O. 1982. A new genus of shark from the Middle Formation of Western Canada. In CAVIN, L., LONGBOT- Triassic of Monte San Giorgio, Switzerland. Palaeontology, 25, TOM, A. and RICHTER, M. (eds). Fishes and the break-up 399–412. of Pangaea. Geological Society, Special Publications, London, SCHAEFFER, B. 1973. Fishes and the Permian–Triassic 295, 9–41. boundary. In LOGAN, A. and HILLS, L. V. (eds). The —— DE BLANGER, K. and NEUMAN, A. G. 2007. Elasmo- Permian and Triassic systems and their mutual boundary. Mem- branchs from the Lower Triassic Sulphur Mountain Formation oir of the Canadian Society of Petroleum Geologists, 2, 493–497. near Wapiti Lake (BC, Canada). Zoological Journal of the Lin- SCHULTZE, H. P., SOLER-GIJO´ N, R., HAMPE, O. and nean Society, 149, 309–337. HEWARD, A. 2008. Vertebrates from the Gharif Formation, —— NEUMAN, A. G. and DE BLANGER, K. 2008. Homal- Lower Permian of Oman [abstract]. 41–42. In Sˇ TAMBERG, odontus nom. nov., a replacement name for Wapitiodus Mut- S. and ZAJI´ C, J. (eds). Faunas and palaeoenvironments of the ter, de Blanger and Neuman, 2007 (Homalodontidae nom Late Palaeozoic – Special Publication for the 5th Symposium on nov., ?Hybodontoidea), preoccupied by Wapitiodus Orchard, Permo–Carboniferous Faunas, 7–11 July 2008. Museum of East- 2005. Zoological Journal of the Linnean Society, 154, 419–420. ern Bohemia, Hradec Kra´love´, 80 pp. NEWBERRY, J. S. 1876. Geological Report. 9–118. In: Report SHEN, S.-Z., XIE, J.-F., ZHANG, H. and SHI, G. R. 2009. of the exploring expedition from Santa Fe, New Mexico, to the Roadian–Wordian (Guadalupian, Middle Permian) global pal- junction of the Grand and Green Rivers of the Great Colorado aeobiogeography of brachiopods. Global and Planetary Change, of the West in 1859, under the command of Capt. J. N. Ma- 65, 166–181. comb, Corps of Topographical Engineers. Government Printing SOLER-GIJO´ N, R. 1997. Euselachian sharks from the Late Office, Washington, DC, 152 pp. Carboniferous of the Puertollano Basin, Spain: biostratigraphic NIELSEN, E. 1932. Permo–Carboniferous fishes from East and palaeoenvironmental implications. Modern Geology, 21, Greenland. Meddelelser om Grønland, 86, 63 pp. 137–169. OBRUCHEV, D. V. 1953. Studies on edestids and the works ST. JOHN, O. and WORTHEN, A. H. 1875. Description of of A. P. Karpinsky. U.S.S.R. Academy of Sciences, Works of the fossil fishes. Geological Survey of Illinois, 6, part II, section I, Palaeontological Institute, Publications, 45, 1–86. 245–488. OSSIAN, C. R. 1974. Paleontology, Paleobotany and Facies —— —— 1883. Descriptions of fossil fishes. A partial revision of Characteristics of a Pennsylvanian Delta in Southeastern the Cochliodonts and Psammodonts, including notices of miscel- Nebraska. PhD thesis, University of Texas, Austin, 393 pp. laneous materials acquired from the Carboniferous formations of —— 1976. Redescription of Megactenopetalus kaibabanus David the United States. Geological Survey of Illinois, 7, 55–264. 1944 (Chondrichthyes: Petalodontidae) with comments on its STAHL, B. J. 1999. Chondrichthyes III Holocephali, handbook of geographic and stratigraphic distribution. Journal of Paleontol- paleoichthyology, Vol. 4. Verlag Dr. Friedrich Pfeil, Mu¨nchen, ogy, 50, 392–397. 164 pp. OWEN, R. 1867. On the mandible and mandibular teeth of STENSIO¨ , E. A. 1921. Triassic fishes from Spitsbergen, Part I. cochliodonts. Geological Magazine, 4, 59–63. Adolf Holzhausen, Vienna, 307 pp. PATTERSON, C. and SMITH, A. B. 1987. Is the periodicity —— 1932. Triassic Fishes from East Greenland. Meddelelser om of extinctions a taxonomic artefact? Nature, 330, 248–251. Grønland, 83, 1–305. PETERS, S. E. 2006. Macrostratigraphy of North America. TARVER, J. E., BRADDY, S. J. and BENTON, M. J. 2007. Journal of Geology, 114, 391–412. The effects of sampling bias on Palaeozoic faunas and implica- REES, J. 2008. Interrelationships of Mesozoic hybodont sharks tions for macroevolutionary studies. Palaeontology, 50, 177– as indicated by dental morphology – preliminary results. Acta 184. Geologica Polonica, 58, 217–221. THIES, D. 1995. Placoid Scales (Chondrichthyes: Elasmobran- —— and UNDERWOOD, C. J. 2002. The status of the shark chii) from the Late Jurassic (Kimmeridgian) of Northern Ger- genus Lissodus Brough, 1935, and the position of nominal many. Journal of Vertebrate Paleontology, 15, 463–481. Lissodus species within the Hybodontoidea (Selachii). Journal TINTORI, A. 1998. New chondrichthyan fauna from the of Vertebrate Paleontology, 22, 471–479. Guadalupian (middle Permian) of the Sultanate of Oman. In KOOT ET AL.: CHONDRICHTHYANS FROM THE WORDIAN KHUFF FORMATION OF OMAN 343

GINTER, M. and WILSON, M. V. H. (eds). Ichthyolith WHITE, E. I. 1968. Devonian fishes of the Mawson-Mulock Issues, Special Publication, 4, 48–49. area, Victoria Land, Antarctica – Trans-Antarctic Expedition TRAUTSCHOLD, H. 1874. Die Kalkbru¨che von Mjatschk- 1955–1958, Scientific Reports no. 16. Geology, 5, 1–26. owa. Eine Monographie des oberen Bergkalks. Erste Ha¨lfte. WILIMOVSKY, N. J. 1954. Gunnellodus, a new name for Idi- Nouveau Me´moires de la Socie´te´ Impe´riale des Naturalistes de acanthus Gunnell. Journal of Paleontology, 28, 693. Moscou, 14, 3–82. WILLIAMS, M. E. 1998. A new specimen of Tamiobatis vetu- TURNER, S. and YOUNG, G. C. 1987. Shark teeth from the stus (Chondrichthyes, Ctenacanthoidea) from the Late Devo- early Middle Devonian Cravens Peak Beds, Georgina Basin, nian Cleveland Shale of Ohio. Journal of Vertebrate Queensland. Alcheringa, 11, 233–244. Paleontology, 18, 251–260. TWAY, L. E., HARRISON, W. E. and ZIDEK, J. 1986. WOODWARD, A. S. 1891. Catalogue of the fossil fishes in the Thermal alteration of microscopic fish remains; an initial British Museum, Vol. 2. British Museum (Natural History), study. Palaios, 1, 75–79. London, xliv + 567 pp. TWITCHETT, R. J. 2001. Post-Permian Radiation. Encyclope- YAMAGISHI, H. and FUJIMOTO, T. 2011. Chondrichth- dia of life sciences. Nature Publishing Group, London (http:// yan remains from the Akasaka Limestone Formation (Middle www.els.net). Permian) of Gifu Prefecture, Central Japan. Bulletin of the WANG, N.-Z., ZHU, X. S., JIN, F. and WANG, W. 2007. Chon- Kanagawa Prefectural Museum, Natural Science, 40, 1–6. drichthyan microremains under Permian–Triassic boundary ZANGERL, R. 1979. New Chondrichthyes from the Mazon both in Zhejiang and Jiangxi provinces, China – Fifth report on Creek fauna (Pennsylvanian) of Illinois. 449–500. In NITE- the fish sequence study near the Permian–Triassic boundary in CKI, M. N. (ed.) Mazon creek fossils. Academic Press, New South China. Vertebrata Palasiatica, 45, 13–36. York, 606 pp. —— ZHANG, X., ZHU, M. and ZHAO, W.-J. 2009. A new —— 1981. Chondrichthyes I Paleozoic Elasmobranchii, handbook articulated hybodontoid from Late Permian of northwestern of paleoichthyology, Vol. 3A, Gustav Fischer Verlag, Stuttgart, China. Acta Zoologica, 90, 159–170. 115 pp.