Preliminary report of an Upper Cretaceous elasmobranch fauna from Ryazan Oblast, Russia Sergey Solonin (1), Ryan Shell (2), Alexey Vodorezov (1), Robert Niedźwiedzki (3) 1) Ryazan State University, Ryazan Oblast, Russian Federation 2) Wright State University, Ohio, United States 3) Institute of Geological Sciences, University of Wrocław, Lower Silesia, Poland Background Discussion Results & 1.0cm A B DISCUSSION With 24 elasmobranch genera and 35 species, this locality contains one of the highest diverse elasmobranch assemblages anywhere in the Mesozoic of Russia. There are taxa belonging to many different trophic groups: durophagous fishes adapted to crushing or grindng of benthic hard-shell preys (e.g., Ptychodus), nektonic apex predators that feed on large fishes and/or reptiles (e.g., Cretoxyrhina, Squalicorax, Archaeolamna), and typical piscivorous taxa (e.g., Scapanorhynchus). This suggests that the Late Cretaceous seas of western Russia likely contained high primary productivity among invertebrates (the presumed prey of hybodontiforms) as well as nektonic animals, which were preyed upon by a diverse group of piscivorous sharks. Among the elasmobranchs adapted for nektonic carnivory, the Lamniformes make up most of the diversity observed here. However, the large proportion of damaged teeth and the presence of species typical for the Cenomanian suggest that part of the teeth could have been be redeposited and time averaged. METHODS AND MATERIALS Some 500 kg of sand was collected from the fossiliferous bed during field seasons in 2017-2019. The chondrichthyan material was obtained by bulk sampling and subsequent screen washing of the fossiliferous sediments with the use of sieve with a mesh size of 5, 3, 1 and 0.5 mm. The teeth were picked from part of residues under binocular stereomicroscope BM-51-2 (magnification 8.75) and magnifying glass. Additionally, a smaller portion of the specimens (mostly large teeth) was surface- collected directly in the quarry. In 2017, specimens were collected only from outcrops. In 2018, a sample of 250 kg was collected. The sediment was sifted through 5 and 1 mm sieves. Sometimes an intermediate sieve with a 3 mm mesh size was used. In 2019, a sample of 250 kg was collected. The sediment was sifted through sieves with 5, 1 and 0.5 mm mesh size. Part of the remaining sifted sediment (~50 kg) was taken to the laboratory to be picked for teeth under stereomicroscopes and magnifying glasses. In total about 200 complete (crown with root) and about 900 partially complete (crown with part of the root) elasmobranch teeth were collected. Numerous (about 1100) unidentifiable fragments of crowns or roots of elasmobranch teeth were observed but not studied. ELASMOBRANCHII Figure 4 consists of a tentative list of elasmobranch taxa recovered in the Malyy Prolom quarry thus far. Genera and species are reported with their associated families, and all are color coded at the ordinal level: green represents the Hybodontiformes, brown – the Squatiniformes, pale blue - the Synechodontiformes, orange - the Squaliformes, light red - the Orectolobiformes, blue - the Lamniformes, and violet - the Rajiformes. Shark teeth dominate among elasmobranch fossils both in terms of the number of specimens and number of taxa (23 genus, 34 species). Batoids represent only a few teeth belonging to one genus and species. Chimaeroid remains are absent. Among the shark remains, Lamniformes make up the largest component at this locality. Hybodontiformes are represented by multiple families and numerous specimens, especially of Ptychodus. Teeth of the Orectolobiformes are also relatively numerous. The other orders: Squaliformes, Squatiniformes and Synechodontiformes, are fewer in species and represented by only one or two family each. The selachian material is generally poorly preserved. Only 9% of material is well preserved as complete teeth without any signs of abrasion (Fig. 5). Other teeth are broken to varying degrees and many crowns of teeth are abraded. GEOGRAPHICAL AND GELOGICAL BACKGROUND The studied elasmobranch teeth assemblage was recovered from an active sand quarry near the village of Malyy Prolom located in about 5.0 km to NW from Shatsk in SE part of Ryazan Oblast (Fig. 1, 2). Area of Ryazan Oblast geologically is located in the SE part of the Moscow Syneclise in the central part of the Russian Platform (East European Platform) [1]. Sedimentary rocks of the Mesozoic, represented by Middle Jurassic, Upper Jurassic, and Cretaceous deposits rest directly on the Carboniferous System in Ryazan Oblast. The large stratigraphic gap including Turonian and Coniacian stages exists in Cretaceous stratigraphy of the Ryazan region ([2], [3]). In the Malyy Prolom area, directly below Quaternary sediments, Santonian quartz sands and sandstones (Dmitrov Fm.) occur, and are underlain by Cenomanian quartz sands (Yakhroma Fm.) and Albian clays and silts (Paramanovsk Fm.) ([1], [4]). Sands of different geological stages are separated by distinct erosional unconformites ([1] [5], [6]). Sands of the Paramanovsk Fm. were formed in relatively deep-marine environment of offshore ([2], [7]), while sedimentation of the Yakhroma and Dmitrov Fms. took place in marine shore-face zone [2]. All sandy units listed above were deposited in the North-Eastern Peri-Tethys basin which was well connected with West Siberian sea and with marine basins of Central Europe [8]. Biostratigraphy of Albian – Santonian deposits of SE part of the Moscow Syneclise is based on radiolarians and ammonites for Albian and lower Cenomanian rocks and on inoceramids for the upper Cenomanian – Santonian interval ([1], [2], [5], [9]). STUDIED QUARRY The Malyy Prolom quarry exposes 4.5 m fine-grained Cretaceous quartz sands or quartz- glauconite sands covered by 1.6 m of Quaternary sediments (Fig. 3). Cretaceous rocks do not contain body fossils except the layer of coarse-grained sand in upper part this unit (0.1 - 0.6 m), where numerous elasmobranch teeth, rare vertebrae and teeth of actinopterygian fishes, very rare shell fragments or molds of bivalves, and extremely rare teeth of marine reptiles occur. This fossiliferous bed also differs from underlying and overlying sand layers in larger grain diameter and presence of phosphated pebbles of sandstones and siliceous sandstone concretions. The fossiliferous bed is the only Cretaceous bed which lies on a strongly eroded surface [10]. Unfortunately, the Cretaceous sands of the Malyy Prolom quarry have not yielded any stratigraphically important taxa. However, analyses of geological maps of the region [3] and geological profiles of nearby boreholes from Karnauhovo (3 km from studied quarry) suggest that the uppermost part of the Cretaceous sands, which is separated from underlying beds by a erosional surface, is Santonian in age, while the underlying sand layers are Cenomanian. Moreover, according to [1] the distinguishing feature of the Santonian in the SE part of the Moscow Syneclise is the presence of siliceous sandstone concretions in Santonian sands. Such forms occur in the fossiliferous bed of the Malyy Prolom quarry. LITERATURE CITED [1] Kuzmin A.N. et al. 2015. State Geological Map of the Russian Federation at a scale 1: 1,000,000, sheet N-37 (Moscow), Explanatory memorandum). Kartograf. fabrika VSEGEI, SPb, 496p. [2] Sahagian D. et. al. 1996. Eustatic curve for the Middle Jurassic-Cretaceous based on Russian platform and Siberian stratigraphy: zonal resolution. AAPG Bull., 80: 1433-1458. [3] Fadeeva L.I., Iosifova Iu.I. 1998. Geological Map of pre-Quaternary deposits of the Ryazan region. Scale 1: 500,000. Mezhregionalnyi tsentr po geologicheskoi kartografii, Moskva. [4] Drutskoi S.V., Fadeeva L.I. 2001. Explanatory memorandum to the geological maps of Quaternary and pre-Quaternary deposits of the Ryazan region at a scale of 1: 500,000. Mezhregionalnyi tsentr po geologicheskoi kartografii, Moskva, 57p. [5] Sidorenko A. V. 1971. Geology of the USSR. Volume IV. Center of the European part of the USSR. Geological description. Izdatelstvo Nedra, Moskva, 742p. [6] Nikitin, S.N. et. al. 1984. Report on aerial photo-geological mapping at a scale of 1: 200,000 of the Oka-Tsninsk swell area. Moskovskaia Geologorazvedochnaia Ekspeditsiia, Moskva, 334p. Fig.5. Some elasmobranch teeth from Malyy Prolom. 1. Ptychodus altior, a- lateral view, b- lingual view. 2. P. marginalis, a- occlusal view, b- lateral view. 3. P. aff. anonymus, a- lateral view, b- occlusal view. 4. Polyacrodus cf. maiseyi, a- lingual view, b- labial view. 5. Protosqualus sp., a- lingual view, b- labial view. 6. Cederstroemia sp., a- lingual view, b- labial view. 7. Synechodus sp., a- lingual view, b- labial view. 8. Squalicorax sp., a- lingual view, b- labial view. 9. Squalicorax aff. S. mutabilis, a- lingual view, b- labial view. 10. Scapanorhynchus sp., a- lingual view, b- labial view. 11. Archaeolamna ex.gr. kopingensis, a- lingual view, b- labial view. 12. Cretalamna ex.gr. appendiculata, a- lingual view, b- labial view. 13. Cardabiodon sp., a- lingual view, b- labial view. 14. Cretoxyrhina mantelli, a- lingual view, b- labial view. 15. Squatirhina sp. , a- labial view, b- distal view. Scale bar 10 mm. Fig. 1. Location of the study area (https://www.google.ru/maps). Fig. 2. Geological sketch-map of the area surrounding the Malyy Prolom quarry (modified after [3]). Fig. 4. Preliminary list of elasmobranch taxa from Malyy Prolom. Fig. 3. Generalized stratigraphic column of the Malyy Prolom quarry. [7] Starodubtseva I.A., Sennikov A.G., Soroka I.L. 2008. Geological History of Moscow Region in the Collections of Natural Museums of the Russian Academy of Sciences. Gosud. Geolog. Muzey im. V.I. Vernandskogo RAN; Paleontologichesky Institut RAN, Moskva, 229 pp. [8] Baraboshkin E.Y., Alekseev A.S., Kopaevich L.F. 2003. Cretaceous palaeogeography of the North-Eastern Peri-Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology, 196: 177–208. [9] Olferev, A.G., Alekseev, A.S. 2005. Stratigraphic diagram of the Upper Cretaceous deposits of the East European Platform. Explanatory memorandum. Paleontologicheskii Institut RAN, Moskva, 204p. [10] Krivtsov V.A., et al. 2018. The potential of creating and using protected areas of geological and geomorphological interest in the Ryazan region. Vestnik Ryazanskogo Gosud. Univers. im. S.A. Yesenina, 3(60): 108-119. ACKNOWLEDGMENTS We deeply thank Jun A. Ebersole, David J. Cicimurri, Shawn A. Hamm, Gerard R. Case and Guillaume Guinot for useful comments on several specimens.