ISSN 00310301, Paleontological Journal, 2015, Vol. 49, No. 10, pp. 1112–1124. © Pleiades Publishing, Ltd., 2015.

The First Find of Permian Ceratodontids (Dipnoi, Osteichthyes) in Russia O. A. Lebedeva, A. G. Sennikova,b, V. K. Golubeva,b, N. I. Krupinac, G. Niedzwiedzkid, and T. Suleje aBorissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia email: [email protected], [email protected], [email protected] bKazan Federal University, Kremlevskaya ul. 18, Kazan, 420008 Russia cEarth Science Museum, Moscow State University, Moscow, 119991 Russia email: [email protected] dDepartment of Organismal Biology, Evolutionary Biology Center, Uppsala University, Norbyvägen 18A, Uppsala, 75236 Sweden email: [email protected] eInstitute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, Warsaw, 00818 Poland email: [email protected] Received January 30, 2015

Abstract—A huge dipnoan, Permoceratodus gentilis Krupina, gen. et sp. nov. (order Ceratodontiformes), from the terminal Permian beds (Zhukovian Regional Stage, Vyatkian Stage, Upper Permian) of the Sokovka locality (Vladimir Region) is described. It is characterized by the evolutionarily advanced high extent of fusion of skull roof bones and conservative well defined structures of the seismosensory system of the head. This combination distinguishes the new taxon from other Ceratodontiformes. A set of conservative and advanced characters is observed in many vertebrates of the Vyazniki faunal assemblage. Large tetrapods and fishes characterize the terminal developmental stage of the Permian fauna of Eastern Europe, which was fol lowed by impoverishment of the taxonomic composition accompanied by a decrease in body size. The dip noan described here, like some other vertebrates of this assemblage, belong to highrank taxa, which had just appeared in the Paleozoic, but reached flourishing in the Mesozoic.

Keywords: Ceratodontiformes, lungfish, paleosynecology, ecological crisis, Upper Permian, Upper Vyatkian, Russia, Vladimir Region

DOI: 10.1134/S0031030115110052

INTRODUCTION HISTORICAL ACCOUNT Among Late Permian vertebrate localities of the The Vyazniki vertebrate fauna was discovered dur East European Platform, a group of Vyazniki localities ing B.P. Vjuschkov’s (Paleontological Institute, Acad (Fig. 1) occupies an important place. It is situated on emy of Sciences of the USSR, Moscow: PIN) excava the right bank of the Klyazma River in the town of tions in 1951, 1955, and 1956. Vjuschkov dated it by Vyazniki (Vladimir Region) (Efremov and Vjuschkov, the Severodvinian Age based on relatively small rep 1955; Sennikov and Golubev, 2006b; Newell et al., tiles, which he regarded as insufficiently derived com 2010). In this area, the Vyazniki faunal and floral pared to the forms of the terminal Permian Sokolki assemblages of the terminal Permian, which is only fauna including gorgonopians and pareiasaurs and known in European Russia, is particularly representa also based on a conchostracan assemblage identified tive. This assemblage displays the last antecrisis devel by N.I. Novozhilov. Subsequent detailed studies of opmental stage of the continental biota at the very end vertebrates excavated by Vjuschkov undertaken by of the Permian. Therefore, a thorough examination of PIN researchers (Ivakhnenko, 1990; Shishkin, 1990; this assemblage is of great importance for gaining an Sennikov, 1995, 1996; Ivakhnenko et al., 1997; Gol understanding of the causes and processes of the ubev, 1998, 2000a, 2000b; etc.) has demonstrated that Permo–Triassic ecological crisis and mass extinction the Vyazniki assemblage should be dated as terminal on land. Permian, being the youngest in Eastern Europe,

1112 THE FIRST FIND OF PERMIAN CERATODONTIDS (DIPNOI, OSTEICHTHYES) 1113

30° 40° 50° ° 60 Bykovka 7 6 3 4 5 9 8 2 1 Moscow Vyazniki Klyazma River M7 Vyazniki 12

50° 10 1 km 11 13

Fig. 1. Geographical position of the Vyazniki group of localities: (1) Bykovsky Ovrag, (2) Zelenaya Gorka, (3) Bykovskoe Ozero, (4) Bykovka (Vyazniki2), (5) Sokovka (Vyazniki2), (6) Metallist, (7) Petrino, (8) Vyazniki1, (9) Yartsevo, (10) Balymotikha1, (11) Balymotikha2, (12) Tolmachevo, (13) Fedurniki. younger than the Sokolki (pareiasaurian–gorgono and isolated points in European Russia (Sennikov and pian) assemblage (Fig. 2). Golubev, 2005, 2006a, 2006b, 2007, 2013; Sennikov et al., 2014). Similar boundary assemblages have not In 1999, Sennikov renewed field studies in the yet been revealed anywhere in the world. vicinity of Vyazniki and Gorokhovets. He found the previously known bone beds in the Vyazniki locality Joint studies and excavations of the group of (Bykovka, Yartsevo) and discovered a new site, Gor Vyazniki localities were performed by the Borissiak okhovets, which has yielded the taxonomically richest Paleontological Institute of the Russian Academy of Permian vertebrate fauna of the Sokolki Assemblage Sciences, Moscow (PIN); Institute of Paleobiology of (Sennikov et al., 2003). This initiated a thorough and the Polish Academy of Sciences, Warsaw (IPP); and complex study of PermoTriassic faunal and floral the Faculty of Biology of Warsaw University in 2008, localities and reference sections in this region. Since 2010, and 2013, headed by A.G. Sennikov (PIN) and then, experts not only from PIN, but also from the T. Sulej (IPP). In September, 2013, the Sokovka local Geological Institute of the Russian Academy of Sci ity was intensely excavated. This locality is situated in ences, Moscow (GIN), Saratov and Kazan state uni a short and relatively deep gully cutting the right slope versities, and paleontologists and geologists from of the Klyazma River valley in the northwestern sub Poland, Germany, and Great Britain participated in urbs of the town of Vyazniki, just east of a sand quarry this research. near the village of Bykovka. The main excavation was performed in the right slope of the gully, where the fos Since 2003, new Late Permian bonebearing local sils became exposed over an area of about 20 m2 ities with fish and tetrapod fossils were discovered in (Fig. 3) and rich material of Late Permian vertebrates the vicinity of Vyazniki: Sokovka, Metallist, Balymo was collected. In the left slope, at the same hypsomet tikha, etc. (Fig. 1); in addition, the first Early Triassic ric level, excavation was performed within a small area (Vokhmian Regional Stage) vertebrate locality in and yielded only individual isolated vertebrate bones, Fedurniki (Sennikov and Golubev, 2013) was discov including remains of a huge dipnoan found by ered. Insects, ostracods, and macroflora were found G. Niedzwiedzki. This specimen is described below. for the first time. New material of bivalves and con chostracans was obtained; new fish taxa were identi To date, only individual isolated teeth of the dip fied and described. A palynological assemblage similar noan Gnathorhiza have been recorded in the Upper to that of the type section of the Permian–Triassic Permian of European Russia (Minikh, 1977; boundary beds of China is recognized; it displays the M. Minikh and A. Minikh, 1998; A. Minikh and socalled “algal” or “fungal” episode. In general, the M. Minikh, 2009). In the Induan Stage and Lower data on various biotic groups confirmed the suggestion Olenekian Substage of the Lower Triassic, remains of that the Vyazniki assemblage is a separate terminal Gnathorhiza become rather abundant and are used as Permian faunal and floral assemblage (Fig. 2) corre an index form (Minikh, 1977; M. Minikh and sponding to a stage of crisis destabilization of the Per A. Minikh, 1998). The first ceratodontid teeth of the mian biota, showing somewhat transitional state, and genus Ceratodus appear in Russia in the Upper Ole preceding complete extinction. This stage of destabili nekian Substage of the Lower Triassic and extend fur zation was probably rather short and fixed in Vyazniki ther up to the terminal Ladinian Stage of the Middle

PALEONTOLOGICAL JOURNAL Vol. 49 No. 10 2015 1114 LEBEDEV et al.

ISC RSC Regional Tetrapod zone Faunal assemblage stage Stage Stage Series Series System System Substage

Bukobayian Mastodonsaurus assemblage Ladian Ladian

Middle Middle Donguzian Eryosuchus assemblage sian sian Ani Ani Kannemeyeroid superassemblage Trematosaurus subassemblage Gamian Inflectosaurus assemblage Yarengian subassemblage Vyborosaurus– Angusaurus Triassic Triassic lian vkian subassemblage UstmyFedoro

Olenekian Olenekian BenthosuchusAngusaurus assemblage

kian subassemblage Lower Lower Slud Wetlugasaurus Parotosuchus Proterosuchian

superassemblage WetlugasaurusThoosuchus subassemblage Vetlugian Benthosuchus gusevae Rybinskian

assemblage subassemblage Benthosuchus Tupilakosaurus wetlugensis Spasskoe assemblage mian Vokh Induan Induan Zhukovian Archosaurus rossicus Vyazniki assemblage Nefyo Chroniosuchus

Changh dovian Scutosaurus paradoxus karpinskii Sokolki subassemblage Jarilinus Bykovian mirabilis Chroniosaurus Sokolki Scutosaurus Proelginia levis llyinskoe subassemblage permiana Chroniosaurus dongusensis Putya Upper tinian Deltavjatia vjatkensis Kotelnich subassemblage Upper Lower Upper Lower Upper Suchonica vladimiri Sundyr assemblage LLU

Sukhonian Ulemosaurus svijagensis Isheevo assemblage Permian Permian Lower

Urzhumian Ocher Estemmenosuchus sub Mezen Guadalupian Lopingian Wordian Capitanian Wuchiapingian uralensis assemblage Urzhumian Severodvinian Vyatkian

Dinocephalian Theriodontian assemblage superassemblage superassemblage Titanophoneus Biarmian ian singian

nian Golyusherma Ocher LU Parabradysaurus Kaza Road

silantjevi assemblagesubassemglage assemblage Sheshmian

Soli

Ufimian kamskian Clamorosaurus nocturnus Inta assemblage super Cisuralian Cisuralian Tatarian Kungurian assemblage Eryopoidean

Fig. 2. Stratigraphical chart of the PermoTriassic continental beds of Eastern Europe and Cisurals and tetrapod assemblages. Designations: (ISC) International Stratigraphic Chart, (L) Lower, (RSC) General Stratigraphic Chart of Russia, (U) Upper.

PALEONTOLOGICAL JOURNAL Vol. 49 No. 10 2015 THE FIRST FIND OF PERMIAN CERATODONTIDS (DIPNOI, OSTEICHTHYES) 1115

2

1

3

(a) (b)

Fig. 3. Excavation of the terminal Permian vertebrate fauna in the Sokovka locality, in a gully northwest from the town of Vyazniki, Vladimir Region: (a) main excavation in the right slope of the gully: (1) section no. 0446C, (2) section no. 0317, 0446A, (3) excavation in the left slope; (b) prospecting excavation in the left slope of the gully, the point where remains of a large dipnoan were found, view of the right slope of the gully.

Triassic. Those occur regularly everywhere and are and Isadia aristoviensis A. Minikh (Newell et al., 2010; used as index fossils (Minikh, 1977; M. Minikh and A. Minikh et al., 2014) and unidentifiable fragments A. Minikh, 1998). of tetrapod bones. The Vokhma Formation (25–30 m thick) is located STRATIGRAPHY upward in the section. Its lower part (20–25 m thick) is formed by the Zhukov Member, which is composed In the vicinity of the town of Vyazniki, the Permo of brown, reddish brown, crossbedded, polymictic, Triassic red continental beds form more than 140 m from fine to coarsegrained sands and sandstones, thick sequence (Fig. 4). They overlie gray carbonate with lenses of intraformational gravelstones and con beds of the Lower Kazanian Substage with marine glomerates. Gravelstones and conglomerates include invertebrates (Golubev and Sennikov, 2015). The tetrapods of the Vyazniki assemblage, plants, and ter lower part of the red bed sequence (60–65 m) belongs minal Permian fishes and bivalves. This stratigraphic to the Nizhnyaya Ust’ya Formation. It is represented level in the Vyazniki section is particularly rich in ver there by reddish brown clays, with quartz sandstone tebrates. To date, the group of Vyazniki localities interbeds, with gypsum inclusions in the lower part (Vyazniki1, Sokovka, Bykovka, Metallist, Yartsevo, (Singer Member, 45–47 m) and palygorskite in the Petrino: Fig. 1) has yielded the following vertebrate upper part (Malaya Lipka Member, 20–25 m). The assemblage: fishes: the shark Hybodontiformes fam. Nizhnyaya Ust’ya Formation has not yielded fossils; indet.; the lower actinopterygians Mutovinia sennikovi therefore, its age is uncertain. These strata are tradi A. Minich, Mutovinia sp., Strelnia sp., Toyemia blu tionally assigned to the Urzhumian Regional Stage mentalis A. Minich, Toyemia sp., Isadia aristoviensis (Verkhnepermskie …, 1984), although the Kazanian A. Minikh, Isadia sp., Geryonichthys sp. nov., and age of these deposits is more probable from the geohis Evenkia (?) sp.; the chondrostean Saurichthys (?) sp. torical point of view (Golubev, 2004). (Newell et al., 2010; A. Minikh et al., 2014); tetrapods: The Malaya Lipka Member is overlain by the Voi the brachyopoid labyrinthodont Dvinosaurus egregius novo Member of the Obnora Formation (9–10 m Shishkin, Microsauria (?) fam. indet., the seymouri thick). This member is composed of quartz sand and amorph (karpinskiosaurid) Karpinskiosaurus secundus yellow, gray, brown, beige, and red massive or horizon (Amalitzky), the bystrowianid chroniosuchian tally laminated, finegrained sandstones. There are Bystrowiana permira Vjuschkov and chroniosuchid interbeds from several centimeters to 3 m thick of Uralerpeton tverdochlebovae Golubev; the nycterole brown, red, gray, dark gray, horizontal laminated clays, terines (elginiids) Obirkovia sp. and Elginiidae gen. in places, with pyrite and abundant plant remains indet., the proterosuchid Archosaurus rossicus Tatar (macrofossils and palynomorphs), bivalves, ostracods, inov, the dicynodont Dicynodontidae gen. indet., the conchostracans, insects, and vertebrates of the therocephalians (whaitsioids) Moschowhaitsia vjusch Vyazniki biotic assemblage. Vertebrate remains are kovi Tatarinov, Megawhaitsia patrichae Ivakhnenko, represented by scales, teeth, and dermal bones of the and Therocephalia gen. et sp. nov. Zhukov sands and basal actinopterygians Mutovinia sennikovi A. Minich sandstones contain interbeds (several centimeters

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Series Stage Substage Regional Stage Zone Formation Member Fedurniki

9 Ryabi Induan wetlugensis Vokhmian Tupilakosaurus Lower Triassic 4–8 Bykovka

Sokovka 1 (outcrop nos. 0317, 0446A) and sandstone, (3) silt siltstone, , level of dipnoan fish occurrence, (20) fishes, , level 10 m (12) gray beds, (13–21) fossils: (13) macrofossils of (12) gray 8 2 6

Archosaurus rossicus 4 2 Upper insects, (19) vertebrates Zhukovian 0 3 4 Sokovka (outcrop Cape Bykovka no. 0446C) 5 (2) s gion. Designations: (1) conglomerate, 1 15 3 4 6 14 13 5 12 10 6 acans, (17) ostracods, (18)

8 8 outcrop no. 1032 4

1 rock, (10) red beds, (11) variegated interval, (9) overgrown

1 13 Vladimir Re ns near the town of Vyazniki,

2 14 (16) conchostr (15) bivalves, 3 15

18–21 4 16 17 15 5 17 14 12 6 18 Kazanian Vyatkian 11 7 19 Nizhnyaya Ust’ya9 Obnora Vokhma 6–8 8 20 outcrop no. 0915, 1031 Middle Permian (Biarmian)5 Upper Permian (Tatarian) 9 21 4 10 22 3 2 11 12 sectio and Triassic Correlation of Permian

Singer1 Malaya Lipka Voinovo Zhukov Fig. 4. (4) silty clay, (5) clay, (6) marl, (7) gypsum, (8) palygorskite, (5) clay, (4) silty clay, terrestrial plant organs, (14) palynomorphs, terrestrial plant organs, (14) palynomorphs, (21) tetrapods, (22) plant roots (paleosol).

PALEONTOLOGICAL JOURNAL Vol. 49 No. 10 2015 THE FIRST FIND OF PERMIAN CERATODONTIDS (DIPNOI, OSTEICHTHYES) 1117 thick) of red and brown clays and siltstones with plant Species composition. Type species. roots (paleosol) and remains of terminal Permian Remarks. The ceratodontiform genera most bivalves and insects. similar to the form described belong to an uncertain In the Sokovka locality, bone beds are confined to family or different families; that is, Asiatoceratodus the lower part of the Zhukov Member. The over Vorobyeva, 1967 belongs to Asiatoceratodontidae whelming majority of specimens from this point come Vorobyeva, 1967 and Ceratodus sturii Teller, 1891, to from the right slope of the gully. These bonebearing Ceratodontidae Gill, 1872. This prevents formal com sands, sandstones, and conglomerates are located parison of the new genus with the others within the 5.5 m above the boundary between the Voinovo and family. In this connection, comparison is performed in Zhukov members (Fig. 4). The dipnoan specimen was the section Remarks. found during excavation in the left slope of the gully In Jurassic Potamoceratodus guentheri (Marsh, 35 m west of the main excavation area, approximately 1878) and Triassic Ceratodus sturii Teller, 1891, as in at the same hypsometric level. In our opinion, the the new genus, skull roof bones are intensely fused to same bone beds as in the right slope are exposed there. form a Tshaped posteromedial block (Fig. 6). The The Voinovo Member of the Obnora Formation new form differs from these species in the even more and Zhukov Member of the Vokhma Formation are complete fusion of roof bones into three rather than characterized by terminal Permian faunal and floral five blocks. In both forms, the skull roof is much wider assemblages. In the Permian section of the East Euro and shorter than in Permoceratodus gen. nov. In pean Platform, the beds with this biotic assemblage P. guentheri (Fig. 6a), grooves of the seismosensory termed Vyazniki are allocated to the Zhukovian system are only represented by short, strongly curved Regional Stage. segments in the anterolateral part of the skull roof, The Zhukov Member is overlain by the lithologi while in C. sturii (Fig. 6b), the otic branch of the canal cally similar Ryabi Member of the Vokhma Formation is displaced strongly laterally. The narrower skull roof (6–7 m thick), composed of interbedding of yellowish pulls Permoceratodus gen. nov. close to Asiatoceratodus brown, reddish brown, crossbedded, polymictic atlantis (Martin, 1979) (Fig. 6c), but in the former, the sandstones and brown and reddish brown clays and infraorbital branch apparently deviated on the circu siltstones with bluish gray veins with paleosols. These morbital rather than lateral bone series, although this deposits only occur east of the town of Vyazniki; in its skull part is not preserved. western suburbs, in the area of the Sokovka locality, In members of the family Ptychoceratodontidae they are absent because of erosive processes. In this and Asiatoceratodus atlantis (Martin, 1979), the ptery part of the section, ostracods, conchostracans, scales goid process and, hence, the otic projection of the of actinopterygians, and isolated bones of tetrapods braincase are shifted strongly anteriorly (Kemp, (Tupilakosaurus sp., Contritosaurus (?) sp.) of the 1998). In Permoceratodus gen. nov., this projection is Vokhmian Regional Stage of the Lower Triassic were in a posterior position. found. Thus, in the vicinity of Vyazniki, as in other The combination of the roof ossification type, regions of the basin of the lower reaches of the Oka position of the otic projection, and the extent of devel River, such as Gorokhovets, Gorbatov, and Nizhni opment of cutaneous organs of sense is unusual for Novgorod, the Permian–Triassic boundary falls inside other presently known dipnoans; therefore, the form the Vokhma Formation. in question is assigned to a new genus and species, although it is impossible to refer it to a certain family. Occurrence. Russia, Vladimir Region; terminal SYSTEMATIC PALEONTOLOGY Permian, Upper Vyatkian Substage, Zhukovian Order Ceratodontiformes Berg, 1940 Regional Stage. Ceratodontiformes incertae familiae Genus Permoceratodus Krupina, gen. nov. Permoceratodus gentilis Krupina, sp. nov. Type species. Permoceratodus gentilis Plate 2, figs. 2a and 2b Krupina, gen. et sp. nov.; Russia, Vladimir Region, Etymology. From the Latin gentilis (coming town of Vyazniki; Upper Permian, Upper Vyatkian from the same tribe, relative) in relation to cerat Substage. odontids. D i a g n o s i s. Large fish 1.5 m long or more, with H o l o t y p e. PIN, no. 5543/3, incomplete left lat relatively narrow skull. Skull roof bones are sculptured eral part of skull roof; Vladimir Region, Vyaznikovskii by vessel grooves and small tubercles, fused into two District, town of Vyazniki, Sokovka locality; Upper blocks, posteromediolateral + posterolateral and Permian, Upper Vyatkian Substage, Zhukovian anteromediolateral. Roof bones fusion intense; suture Regional Stage, Vokhma Formation, Zhukov Member. between two blocks hardly discernible. Grooves of seis D e s c r i p t i o n (Figs. 5, 6). The only specimen mosensory canals and pitlines well pronounced; otic (holotype PIN, no. 5543/3) is a posteriorly and branch of canal long and straight. Attachment of otic mesially broken part of the skull roof. The lateral part projection of braincase occupying posterior position. of the anterior margin of the specimen is slightly dam

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Plate 2

ab

4 cm

Explanation of Plate 2 Permoceratodus gentilis Krupina, gen. et sp. nov., holotype PIN, no. 5543/3, incomplete left lateral part of skull roof, Vladimir Region, Vyaznikovskii District, town of Vyazniki, Sokovka locality; Upper Permian, Upper Vyatkian Substage, Zhukovian Regional Stage, Vokhma Formation, Zhukov Member: (a) dorsal and (b) ventral views. aged at the sutural boundary. Judging from the edge crest, which increases in thickness caudally approxi thickness, the mesial part of the anterior margin is bro mately to the crossing with the infraorbital canal. Fur ken off to a considerable extent. The lateral margin of ther posteriorly, a slightly raised, strongly rugose roof the specimen is well preserved. The posterior part of margin forms a shallow notch. The posterolateral roof this roof fragment is slightly convex and, at the margin is occupied by an oblong facet overlapped by midlength of the specimen, a weak bend appears and the operculum (op). extends rostrally, separating the lateral part, which is The dorsal surface is damaged by weathering and inclined slightly ventrolaterally relative to almost hor (or) during preparation. The ventral surface of the roof izontal mesial part. The lateral margin forms a sharp (Fig. 5b) is well preserved anteriorly and laterally,

PALEONTOLOGICAL JOURNAL Vol. 49 No. 10 2015 THE FIRST FIND OF PERMIAN CERATODONTIDS (DIPNOI, OSTEICHTHYES) 1119

(a) (b) (c) AnLa 1 2 3 soc

PoMeLa + PoLa pla ioc fvso fvso oc

fvso pro plp op

Fig. 5. Permoceratodus gentilis Krupina, gen. et sp. nov., holotype PIN, no. 5543/3, incomplete left lateral part of skull roof: (a) dorsal and (b) ventral views; and (c) arrangement of canals presumably for branches of the supraorbital vein. Designations: (AnLa) anterolateral element of skull roof, (PoMeLa + PoLa) posterior mediolateral and posterolateral element of skull roof, (fvso) foramina for large branches of the supraorbital vein; (ioc) infraorbital part of the seismosensory canal, (oc) otic part of the seismosensory canal, (op) area overlapped by the operculum; (pla) anterior pit line of bone J; (plp) posterior pit line; (pro) point of attachment of the otic region of the braincase, (soc) supraorbital part of the seismosensory canal. whereas in the posterior part of the anterior half, the many roof bones of the lateral series and, hence, laminate bone layer is strongly damaged; therefore, it impossibility to identify them, Cavin et al. (2007) sug is impossible to tell whether or not endocranial ele gested a topographical scheme for designation of large ments adjoined this roof part. The mesial part of the blocks of fused bones. According to the nomenclature posterior half of the specimen displays traces of its proposed by these authors, hereinafter we designate attachment. the posterior element of the fragment described as The bones forming the skull roof are fused almost PoMeLa + PoLa (posterior mediolateral + posterior completely (Fig. 5a; Pl. 2). Only the dorsal surface lateral). According to this nomenclature, the anterior bears a hardly visible suture (indiscernible on the ven element is designated as AnLa (anterior lateral). tral side) between the anterolateral element and remaining part of the roof, which is formed of com The sculpture of dermal bones is in general poorly pletely fused bones. Only the mesial margin of the pronounced ridged and pitted. In the anterior part of anterior part of the holotype has a straight simple the bone AnLa, ridged ornamentation extends rostro sutural surface along contact with a mesially positioned caudally. Ornamentation character is significantly bone (which is absent). Based on the position of refer influenced by numerous large and small branching ence elements, such as pit lines and seismosensory blood vessel grooves. canals, the authors suggest that the posterior part of the fragment is formed of a block of bones fused without a The anterior part (AnLa) of the ventral side of the suture, including I + J + Y1 + Y2 + X bones; and specimen and the lateral region of PoMeLa + PoLa the anterior part is a complex L + M bone. At the display uniform fine ridges characteristic of the grow same time the position of the bone K is uncertain. In ing zones and attachment areas of connective tissue. Carboniferous Sagenodus (Schultze, 1981), this ele Anteriorly, these ridges are directed rostrocaudally; ment is fused with the bone X, on which the infraor posteriorly, they turn gradually laterally to form a fan bital canal branches off. Based on irregular fusions of shaped pattern.

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(a) (b) (d) AnMe AnMe

AnMe soc AnLa AnLa soc soc AnLa ocPoMe + PoMeLa PoLa PoMe + PoMeLa oco

ioc soc AnMe (c) PoMeLa + PoLa oc AnLa oc PoLa PoMe PoMeLa oco

Fig. 6. Structural types of the skull roof in some Ceratodontiformes, characterized by skull roof bones fused in extensive blocks: (a) Potamoceratodus guentheri (Marsh, 1878); (b) Ceratodus sturii Teller, 1891; (c) Asiatoceratodus atlantis (Martin, 1979); (d) Per moceratodus gentilis Krupina, gen. et sp. nov. Designations: (AnLa) anterolateral element of the skull roof, (AnMe) anteromedial element of the skull roof, (PoLa) posterolateral element of the skull roof, (PoMe) posteromedial element of the skull roof, (PoMe + PoMeLa) posteromedial and posteromediolateral elements of the skull roof, (PoMeLa + PoLa) posteromediolateral and posterolateral element of the skull roof, (ioc) infraorbital branch, (oc) otic branch, (soc) supraorbital branch of the seismo sensory canal of the head.

The medial part of PoMeLa + PoLa (Fig. 5b; rior part, it forms a bend and passes almost parallel to Pl. 2) is occupied by the attachment area of the dor the edge. The most rostral part of the canal groove sally ossifying cartilaginous process of the otic projec becomes shallower and, at the anterior margin of tion of the braincase (Fig. 5b, pro). The lateral wall of AnLa, disappears. this attachment is massive, projects strongly ventrally, The seismosensory grooves are relatively shallow, forming a pocketlike depression. The anterior and suggesting that the canal tube was located rather high posterior edges of attachment are ossified to a lesser in the skin and that the dermal layer covering the skull extent and look like low ridges. In the posteromedial roof was relatively thick. part of this attachment zone, the ventral surface of car tilage ossification bears small pits, which may be traces Close to the middle of PoMeLa + PoLa, a narrow of the internal ear structures; however, the insufficient and deep sulcus of the anterior pit line marking the J preservation of this zone prevents more exact interpre bone extends obliquely posteromedially from the tation. beginning of the supraorbital branch to a large fora The groove pattern of the supraorbital (Fig. 5a, soc), men for a blood vessel (Fig. 5a, pla). On the broken infraorbital (Fig. 5a, ioc), and otic (Fig. 5a, oc) posterior margin, a small part of the posterior pit line branches of the seismosensory canal system are char of the Y and I bones is preserved (Fig. 5a, plp). acteristic of many ceratodontids. The otic branch of The largest vessels, presumably branches of the the seismosensory canal is almost straight, it runs ros supraorbital vein (compare with SäveSöderbergh, trally almost to the midlength of the specimen, termi 1952, textfig. 12), run along the ventral side of the nating far from reaching the point of contact between skull roof, penetrating onto the surface through large PoMeLa + PoLa and AnLa. At this point, the infraor foramina in PoMeLa + PoLa (Fig. 5c). The preserved bital canal deviates laterally and, at the bone edge, dis surface has four foramina of this kind (Fig. 5c, fvso), tinctly bifurcates. The supraorbital branch runs which are positioned in a semicircle (counterclock mesially, then turns laterally at an obtuse angle at the wise): in the middle of the broken mesial margin, in suture between PoMeLa + PoLa and AnLa, closely the mesial third of PoMeLa + PoLa, at the poster approaching the lateral bone edge; further, in the ante omesial end of the anterior pit line, and in the poste

PALEONTOLOGICAL JOURNAL Vol. 49 No. 10 2015 THE FIRST FIND OF PERMIAN CERATODONTIDS (DIPNOI, OSTEICHTHYES) 1121 rior third of this bone. Gradually flattening grooves 1981; Kemp, 1998): posteromedial PoMe + PoMeLa extend rostrally from two anterior foramina and, later (A + B + I + J), anteromedial AnMe (E + C), ante ally, from two posterior foramina. Lateral to the sec rolateral AnLa (L + M after Kemp or K + L + M + N ond, there is a shallow and rather wide groove, but its after Schultze), and posterolateral PoLa (Y + Z). In posterior end falls on the lost bone fragment, so that it other ceratodontids, for example, Ptychoceratodus, is impossible to recognize whether or not it came out bones are fused in varying combinations of blocks of a foramen in the skull roof. (Kemp, 1998). The roof fragment described here On the ventral side of the specimen, four branches shows an even more complete involvement of bones of partially enclosed inside the bone diverge laterally the lateral series (I + J + Y + X) into an integrated from the rostrocaudally directed groove of the canal complex (PoMeLa + PoLa). Intense fusion is typical occupying the most mesial position in the posterior part for Mesocenozoic forms, in contrast to Paleozoic taxa, of PoMeLa + PoLa; they branch or do not branch and distinguishing Permoceratodus gentilis gen. et sp. nov. come onto the dorsal surface of the specimen through from those. the foramina described above (Fig. 5b, fvso) at some It is not improbable that the posteromedial part of distance from each other. The walls of the abovemen the specimen also includes the bones A and B, but the tioned rostrocaudal groove are covered by a compact incomplete preservation prevents reliable resolution of bone layer, smooth, distinctly separating this structure this question. In any case, expansion of the postero from surrounding spongy bone tissue. The width and medial block of bones in ceratodontids due to inclu depth of the groove vary, apparently because of the sion of bones of the paramedial series has already been presence of loops and sinuses of the vessel. shown in other taxa (see, for example, Schultze, Material. Holotype. 1981). The fact that, in the evolution, bones were fused mostly in the mediolateral direction additionally sup ports the assumption that the paramedial and lateral DISCUSSION series are included in the posteromedial block in Per Evolutionary Significance of Morphological Features moceratodus gentilis gen. et sp. nov. Based on these of Permoceratodus conclusions, we reconstructed the skull roof (Fig. 6d) according to the type observed in Potamoceratodus The first Early Triassic members of the genus Cera guentheri (Marsh, 1878) and Ceratodus sturii Teller, todus in European Russia were relatively small; subse 1891, with wide, Tshaped posteromedial blocks of quently, up to the end of the Middle Triassic, they roof bones (Figs. 6a, 6b), in contrast to Asiatoceratodus gradually increased in size, but remained smaller than, atlantis (Martin, 1979) (Fig. 6c), in which the poster for example, Bathonian (Middle Jurassic) Ceratodus omediolateral block remains separate. from the Moscow Region (Krupina, 1995). The dip The holotype of Permoceratodus gentilis demon noan found in Vyazniki is comparable in size to Mid strates both advanced and primitive dipnoan charac dle Jurassic forms, exceeding in size all dipnoans ters: strong fusion of skull roof bones into large blocks known from the Triassic of Eastern Europe. Triassic versus preservation of a complete set of seismosensory and Jurassic ceratodontids known from other regions canals and pit lines and also preservation of the poste of the world also reach large size (see, for example, rior position of the jaw articulation. In the younger, Kemp, 1998). Mesocenozoic ceratodontids, the grooves and pit lines Because of incomplete preservation of the speci are reduced to varying extent (see, for example, men, it was initially difficult to determine not only its Kemp, 1998, textfigs. 11D, 13E, 14G). In addition, taxonomic position, but also a part of the skeleton it in this dipnoan lineage, the jaw articulation is dis represented. To refer the cranial fragment in question placed anteriorly (for example, Kemp, 1998, textfigs. to dipnoans, grooves of the seismosensory canal and 13D, 14F) in accordance with lower jaw shortening. pit lines were helpful. The high degree of fusion The jaw articulation, being ventral to the otic region, between bones of the lateral series of the skull roof and makes possible to project its position conditionally to also manifestation and arrangement of these grooves the skull roof. The otic region underlies the I bone and are characteristic of the order Ceratodontiformes is located in the posterior part of the skull roof. Berg, 1940, particularly Potamoceratodus guentheri (Marsh, 1878) and Ceratodus sturii Teller, 1891. These forms show extremely high fusion of skull roof bones Permoceratodus as a Typical Element (Fig. 6). of PreCrisis Community In the first species (Fig. 6a), the posteromedial The Vyazniki faunal assemblage includes many PoMe + PoMeLa (A + B + C + I), anteromedial typically Permian groups, such as kotlassiomorphs, AnMe (E + F), anterolateral AnLa (J + K + L + M), the brachyopoid labyrinthodonts Dvinosaurus, the and posterolateral PoLa (X + Y + Z) blocks are specialized anthracosaur chroniosuchians of the fam formed (Pardo et al., 2010). The second species ily Chroniosuchidae, original nycteroleterine elgini (Fig. 6b) demonstrates the same blocks, differing ids, and others. Unexpectedly, small microsaur somewhat in the elements composition (Schultze, amphibians reappear in the fossil record, although

PALEONTOLOGICAL JOURNAL Vol. 49 No. 10 2015 1122 LEBEDEV et al. they were thought to become extinct long before and Moschowhaitsia vjuschkovi and Megawhaitsia flourished as early as the beginning of the Permian. At patrichae and also suddenly appearing large early the same time, in many tetrapod groups, for example, archosaurian proterosuchid Archosaurus rossicus. Like therocephalians, new specialized forms appeared, Permoceratodus gentilis, the last tetrapod taxon is char which, however, did not survive the terminal Permian. acterized by large body size, features of rather primi Some groups typical for the Triassic appeared for the tive organization, and extreme specialization in the first time, in particular, the chondrostean fish Saurich skull, lower jaw, teeth, and cervical vertebrae (Senni thys, chroniosuchians of the family Bystrowianidae kov, 1995). After the PermoTriassic extinction in (Bystrowiana), and, what is most important, the earli Eastern Europe, a thecodont similar to Archosaurus est archosaurs, i.e., large predatory thecodonts of the rossicus in size and specialization level, namely, the earliest and primitive family Proterosuchidae (Archo early erythrosuchid Garjainia, appeared as late as the saurus rossicus). However, large and specialized end of the Early Triassic. Similarly, after the appear Bystrowiana and Archosaurus did not survive the Per ance of Permoceratodus gentilis in terminal Permian mian–Triassic boundary. The rise of a new dominant Vyazniki community, the first, although also rather predator and formation of a new thecodont–dicyn small, ceratodontids also appeared in European Rus odont coadaptive pair, which is typical for the Triassic, sia at the end of the Early Triassic. Close analogues of instead of the Late Permian gorgonopian–pareiasaur Permoceratodus gentilis and Archosaurus rossicus are pair, marked a principal shift in the structure of terres also observed among Bystrowianidae; in the Vyazniki trial communities during the Vyazniki time, which assemblage, large Bystrowiana permira suddenly occurred in Eastern Europe before the Permian–Tri appeared. At the beginning of the Triassic, it was assic boundary (Sennikov, 1995, 1996). replaced by a small bystrowianid, Axitectum vjushkovi, Based on available data on the evolution of dip and only in the latter half of the Early Triassic, larger noans within aquatic communities of the East Euro forms of the genus Dromotectum reappeared. pean Platform, the discovery of a new component of The dipnoan described, like some other vertebrates Vyazniki aquatic community, the huge dipnoan Per of the assemblage, belongs to highrank taxa appear moceratodus gentilis, seems unexpected at first glance. ing in the Paleozoic, but flourishing in the Mesozoic. To date, it has been accepted that, at the very end of At the same time, at the generic level, none of these the Permian and beginning of the Triassic, Eastern taxa are known from the Triassic. Europe was only inhabited by small dipnoans of the The presence of very large hybodont sharks, huge genus Gnathorhiza (Minikh, 1977; M. Minikh and A. ceratodontid Permoceratodus gentilis, and huge acti Minikh, 1998; A. Minikh and M. Minikh, 2009). nopterygian Mutovinia sennikovi (Minikh et al., 2014) According to available data, the first large dipnoans of in the Sokovka locality expand our knowledge of the genus Ceratodus appeared in the second half of the Vyazniki aquatic vertebrate community (Sennikov, Early Triassic and survived, increasing in size, up to 1995, 1996), in which the top of the food chain was the terminal Middle Triassic (Minikh, 1977; occupied by a very large chroniosuchid, Uralerpeton M. Minikh and A. Minikh, 1998). tverdochlebovae. This community includes the largest At the same time, sudden appearance of the new members of various vertebrate groups, the phyloge dipnoan Permoceratodus gentilis agrees with the con netic lineages of which ceased to exist in the Permian, cept of Zherikhin and Rautian (1999; Zherikhin, and the community structure is rather complex. This is 2003) and Rasnitsyn (2007, 2012) concerning the the last terminal Permian developmental stage of maximum (dramatic) phase of the biotic crisis, which aquatic vertebrate communities of Eastern Europe is characterized by the appearance of shorttermed destroyed by the PermoTriassic crisis. In Triassic specialized endemic taxa, individual taxa of new postcrisis communities, many groups existing in groups, which became widespread ecological domi Vyazniki community are absent, many appear in the nants at the subsequent stage of community evolution, fossil record after a significant break, but are repre immigrant taxa from other regions or other conti sented by other lowrank taxa. At the very beginning of nents, ancient relict forms, the socalled living fossils the Triassic, in the Induan Time, all components of (Lasarus taxa), which repeatedly appeared in the fossil aquatic vertebrate community were small and less spe record after a long gap, etc. A decrease in the pressure cialized; the structure of community was drastically of coenotic control and regulation gave rise to these impoverished; it was almost monotaxon, strongly unusual forms. In the structure of disturbed aquatic dominated by the brachyopoid labyrinthodont Tupila vertebrate community, with broken internal relation kosaurus. Only in the middle of the Early Triassic ships and coadaptations, many ecological licenses (Early Olenekian), a new diversification in aquatic arose, allowing the introduction of essentially new communities started. However, only at the end of the groups. Early Triassic (Late Olenekian), the taxonomic Thus, the unusual huge ceratodontid with a mosaic diversity, complexity of aquatic community of East combination of conservative and advanced characters ern Europe and diversity of the ecological types is typical for such crisis community as Vyazniki, which included in it reached the antecrisis level of the ter includes large specialized whaitsiid therocephalians minal Permian.

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ACKNOWLEDGMENTS January 26–28, 2015, Program and Abstracts), Moscow, 2015, pp. 27–29. Our field works were supported by the Russian Foundation for Basic Research, project nos. 1304 Ivakhnenko, M.F., Faunal assemblages of tetrapods of the Late Permian of Eastern Europe, Byull. Mosk. O–va Ispyt. 10176, 110401055 (A.G. Sennikov and V.K. Golu Prir., Otd. Geol., 1990, vol. 65, no. 6, pp. 55–59. bev) and the Ministry for Science and Higher Educa tion of Poland, project no. 7986/B/2011/40 (T. Sulej). Ivakhnenko, M.F., Golubev, V.K., Gubin, Yu.M., Kalan dadze, N.N., Novikov, I.V., Sennikov, A.G., and The study (A.G. Sennikov and V.K. Golubev) was Rautian, A.S., Permskie i triasovye tetrapody Vostochnoi also supported by the Russian Government Program Evropy (Permian and Triassic Tetrapods of Eastern for Competitive Growth of Kazan Federal University Europe), Moscow: Geos, 1997. among World’s Leading Scientific and Education Kemp, A., Skull structure in postPaleozoic lungfish, Centers; the Russian Foundation for Basic Research, J. Vertebr. Paleontol., 1998, vol. 18, no. 1, pp. 43–63. project nos. 130500274, 130500592, 140400185, Krupina, N.I., The first find of Jurassic ceratodontids (Dip 140593964; Program of Fundamental Scientific noi) in the Moscow Region, Paleontol. Zh., 1995, no. 2, Studies of the Presidium of Russian Academy of Sci pp. 129–131. ences no. 30 “Evolution of the Organic World and Minikh, A.V. and Minikh, M.G., Ikhtiofauna permi Planetary Processes”; G. Niedzwiedzki was supported Evropeiskoi Rossii (Permian Ichthyofauna of European by a grant of Per Erik Ahlberg (Uppsala University). Russia), Saratov: Izdat. Tsentr Nauka, 2009. We are sincerely grateful to all Polish and Russian col Minikh, A.V., Minikh, M.G., and Andrushkevich, S.O., leagues, who participated in joint expeditions in 2008, Ichthyofauna from the terminal Permian in the vicinity of 2010, and 2013. the town of Vyazniki, Vladimir Region, Izv. Sarat. Univ. Nov. Ser., Ser. Nauk Zem., 2014, vol. 14, no. 2, pp. 91–96. Minikh, M.G., Triasovye dvoyakodyshashchie ryby vostoka REFERENCES Evropeiskoi chasti SSSR (Triassic Dipnoans of the East Cavin, L., Suteethorn, V., Buffetaut, E., and Tong, H., European Part of the USSR), Saratov: Saratov. Gos. Univ., A new Thai Mesozoic lungfish (Sarcopterygii, Dipnoi) with 1977. an insight into postPalaeozoic dipnoan evolution, Minikh, M.G. and Minikh, A.V., Fishes, in Granitsa permi i Zool.J.Linn. 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