A new euselachian shark from the early Permian of the Middle Urals, Russia ALEXANDER O. IVANOV, CHRISTOPHER J. DUFFIN, and SERGE V. NAUGOLNYKH Ivanov , A.O., Duffin, C.J., and Naugolnykh, S.V. 2017. A new euselachian shark from the early Permian of the Middle Urals, Russia. Acta Palaeontologica Polonica 62 (2): 289–298. The isolated teeth of a new euselachian shark Artiodus prominens Ivanov and Duffin gen. et sp. nov. have been found in the Artinskian Stage (Early Permian) of Krasnoufimskie Klyuchiki quarry (Sverdlovsk Region, Middle Urals, Russia). The teeth of Artiodus possess a multicuspid orthodont crown with from four to nine triangular cusps; prominent labial projection terminating in a large round tubercle; distinct ornamentation from straight or recurved cristae; oval or semilu- nar, elongate, considerably vascularized base; dense vascular network formed of transverse horizontal, ascending, short secondary and semicircular canals. The teeth of the new taxon otherwise most closely resemble the teeth of some prot- acrodontid and sphenacanthid euselachians possessing a protacrodont-type crown, but differ from the teeth of all other known euselachians in the unique structure of the labial projection. The studied teeth vary in crown and base morphol- ogy, and three tooth morphotypes can be distinguished in the collection reflecting a moderate degree of linear gradient monognathic heterodonty. The range of morphologies otherwise displayed by the collection of teeth shows the greatest similarity to that described for the dentitions of relatively high-crowned hybodontids from the Mesozoic. The internal structure of the teeth, including their vascularization system is reconstructed using microtomography. The highest chon- drichthyan taxonomic diversity is found in the Artinskian, especially from the localities of the Middle and South Urals. Key words: Chondrichthyes, Elasmobranchii, teeth, Permian, Russia, Urals. Alexander O. Ivanov [[email protected]], Institute of Earth Sciences, St. Petersburg State University, 16 Liniya 29, St. Petersburg, 199178, Russia; Kazan Federal University, 18 Kremlevskaya ul., Kazan, 420008, Russia. Christopher J. Duffin [[email protected]], Palaeontology Section, Earth Science Department, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK; current address: 146, Church Hill Road, Sutton, Surrey SM3 8NF, UK. Serge V. Naugolnykh [[email protected]], Geological Institute of Russian Academy of Sciences, 7, Pyzhevsky per., Moscow, 119017, Russia; Kazan Federal University, 18, Kremlevskaya ul., Kazan, 420008, Russia. Received 31 January 2017, accepted 14 March 2017, available online 31 May 2017. Copyright © 2017 A.O. Ivanov et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. (see details and references in Zangerl 1981; Ginter et al. 2010). Introduction More recently, bulk processing of sediment for microverte- When Louis Agassiz produced his monumental pioneering brate content has vastly increased our knowledge of Mesozoic work on fossil fishes (Agassiz 1833–1843), Carboniferous selachian faunas. Carboniferous and Devonian deposits have chondrichthyans were well represented, as were those from begun to be sampled in a similar fashion (Ginter et al. 2010), Late Triassic and later deposits. Chondrichthyans of what again yielding significant numbers of new taxa. This approach were eventually to be identified as Devonian and Permian age has only recently been applied to sequences of Permian age, were, by contrast, almost totally absent. This sampling gap but the initial results are, as expected, very encouraging (e.g., was later gradually to be filled by descriptions of often par- Johnson 1981, 1996; Ivanov 2005; Koot et al. 2013). tial chondrichthyan skeletons and dentitions from now clas- Chondrichthyan remains are both diverse and abun- sic localities. These include the Cisuralian (lower Permian) dant in the early Permian of the Middle Urals of Russia, of Germany, Bohemia, Oklahoma and Texas (USA); the especially in rocks belonging to the Artinskian Stage Guadelupian (middle Permian) of East Greenland; the (early Permian); the vicinity of Krasnoufimsk (Sverdlovsk Lopingian (upper Permian) Marl Slate (north east England), Region, Middle Urals) is famous for its Artinskian fishes. Kupferschiefer (Germany), Productus Limestone (Pakistan) Symphyseal tooth-whorls of the agassizodontid eugene- and deposits of Montpelier (Bear Lake County, Idaho, USA) odontiform, Helicoprion bessonovi Karpinsky, 1899, were Acta Palaeontol. Pol. 62 (2): 289–298, 2017 https://doi.org/10.4202/app.00347.2017 290 ACTA PALAEONTOLOGICA POLONICA 62 (2), 2017 Institutional abbreviations.—PM SPU, Palaeontological A St. Petersburg Arkhangel'sk Museum, Institute of Earth Sciences, St. Petersburg State University, Russia; NHMUK PV, Fossil Fish Section, Earth Science Department, Natural History Museum, London, UK. S N RUSSIA Pechora I A Moscow T N Material and methods U O Those teeth which have been separated from their enclosing M Kazan' matrix were studied and micrographed using Cambridge Voronezh Perm' Kama CamScan-4 and Tescan VEGA-II XMU scanning electron Yekaterinburg microscopes. One specimen with a broken crown in lon- Volga Ufa L gitudinal section was photographed using an optical Leica A MZ 16 microscope fitted with a digital camera. The internal Volgograd R Chelyabinsk U structure of the teeth of the new taxon was reconstructed utilising a SkyScan 1172 Bruker-microCT (Center for Geo- Environmental Research and Modeling “GEOMODEL”, Research park of St. Petersburg State University). Projection B images were reconstructed using NRecon software into Klyuchiki cross section images having rotated them to an upright posi- Quarry tion in the software DataViewer. CTAnalyzer software was used to correct visualization and interpretation of the recon- structed images, and CTVox software was used to achieve 3D volume rendering. Specimens still adhering to the matrix were observed and photographed using a Leica M205C optical microscope and Leica DFC425 C digital microscope camera. This sys- Ufa River tem was used to produce high-resolution pictures of objects that have a high 3-D type character. Using the multi-focus option and Leica application suite (LAS) software the clear- Krasnoufimsk est images are retained and combined so that the object has optimum focus. The system provides a scale but the object size was checked directly with the specimen next to a stage graticule measuring to the nearest 0.1 mm. Geological setting 1 2km 0 Krasnoufimskie Klyuchiki quarry is located 1 km east of Fig. 1. Maps of Ural (A) and Krasnoufimsk area (B; source of the map the village of Klyuchiki and around 7 km to the north of from https://yandex.ru/maps/) showing the location of Krasnoufimskie the town of Krasnoufimsk, Krasnoufimsk District, Sverd- Klyuchiki quarry. lovsk Region, Russia (Fig. 1). This area belongs to the Yuryuzan-Ay Depression of the Middle Urals. The quarry collected in Artinskian deposits exposed at Divya Gora in extends over an area of 150 m2 and now exposes depos- 1898 (Karpinsky 1899). Further abundant fish remains were its of the Divya Formation (Sarginskian Regional Stage, later discovered in several quarries surrounding the town Upper Substage of the Artinskian; for details of the regional of Krasnoufimsk: Chigvintsevo, Krasnoufimskie Kluchiki, stratigraphy see Chuvashov and Dyupina 1973; Chuvashov Ryabinovka, Selektsiya, Sobolevskiy. In addition to the et al. 1990; Naugolnykh 2014). The deposits exposed in symphyseal tooth-whorls of Helicoprion and numerous iso- the quarry consist of platy marls of grey to yellow-grey or lated teeth of ctenacanthids, euselachians and petalodontids blue-grey color, with intercalations of clay, siltstone, and (Ivanov 2014). These localities have also yielded well pre- limestone. The general thickness of the exposed deposits is served parts of the endoskeleton of euselachian elasmo- approximately 6 m. branch and cochliodont holocephalian (Ivanov 2013, 2014). The palaeontologically richest interval is in the mid- The purpose of the present paper is to describe the dle part of the section and corresponds to the relatively teeth of a new euselachian shark which have been found at dark blue-grey marls. The assemblage of fossils from Krasnoufimskie Klyuchiki quarry. Krasnoufimskie Klyuchiki quarry includes the follow- IVANOV ET AL. —NEW PERMIAN SHARK FROM URALS, RUSSIA 291 ing higher plants: the lycopodiopsid, Ufadedron ufaensis Type species: Artiodus prominens Ivanov and Duffin gen. et sp. nov.; Naugolnykh, 2014; Paracalamites sp., an equisetophyte; see below. the peltasperm Permocallipteris sp.; the vojnovskyan gym- Diagnosis.—As for species, by monotypy. nosperms Rufloria sp. and Lepeophyllum sp. (or so-called Stratigraphic and geographic range.—Late Artinskian “Angarian cordaits”; see Naugolnykh 2001); isolated seeds of (early Permian) of the Middle Urals (Russia). the early coniferophytes Cardiocarpus cordatus (Eichwald) Schmalhausen, 1887, Catpolithes sp., and Cordaicarpus Artiodus prominens Ivanov and Duffin sp. nov. sp.; invertebrates: conulariids; brachiopods; bivalves; the Figs. 2–5. gastropod Worthenia aff. burtasorum (Golovkinsky, 1868); nautiloids Orthoceratites siphonocentralis Krotov, 1885 Etymology: From Latin