Palaeobatrachids (Amphibia, Anura) in the Oligocene Sediments of the “Pirin” Mine (Brezhani Graben, Southwestern Bulgaria)

GEOLOGICA BALCANICA, 41. 1–3, Sofia, Dec. 2012, p. 97–103.

Palaeobatrachids (Amphibia, Anura) in the Oligocene sediments of the “Pirin” Mine (Brezhani Graben, southwestern Bulgaria)

Jean Gaudant1, Milorad Vatsev2

1 USM 203 du Muséum national d’Histoire naturelle et UMR 7207 du CNRS, 17 rue du Docteur Magnan, 75013 Paris, France; e-mail: [email protected] 2 Department of Geology and Paleontology, University of Mining and Geology “St. Ivan Rilski”, 1700 Sofia, Bulgaria; e-mail: [email protected] (Accepted in revised form: November 2012)

Abstract. Skeletons and tadpoles of Anura belonging to the palaeobatrachids have been collected in the fresh- water Early Oligocene sediments of the “Pirin” Mine, near the village of Brezhani, southwestern Bulgaria. Skeletons of cyprinid fishes are also present in the same bituminous argillite. The anatomical study of the palaeobatrachid skeletons has shown that they should be determined as Palaeobatrachus cf. grandipes (Giebel). This new find extends the geographical distribution of this species and of the family Palaeobatrachidae to the southeastern Europe.

Gaudant, J., Vatsev, M. 2012. Palaeobatrachids (Amphibia, Anura) in the Oligocene sediments of the “Pirin” Mine (Brezhani Graben, southwestern Bulgaria). Geologica Balcanica 41(1–3), 97–103. Key words: frogs, palaeobatrachids, skeletons, tadpoles, fresh water, Oligocene, Bulgaria.

Introduction Geological setting (M. V.)

Palaeobatrachus skeletons and tadpoles have been col- The Brezhani Graben is situated at a short distance of the lected by one of us (M.V.) in the Oligocene sediments northwestern part of the Rhodope Unit, between the Pirin of the “Pirin” Mine, in the Brezhani Graben, south- horst block of the Pirin-Pangeon unit eastwards, and the western Bulgaria, together with skeletons of cyprinid second order Vartichovitsa horst westwards (Vatsev, fishes belonging to the genus Protothymallus Laube. 1984). Its basement consists of Proterozoic metamorphic The lithostratigraphy of this area (Fig. 1) was previ- rocks and Cretaceous and Palaeogene granites. The gra- ously described by Vatsev (1984, 1991), whereas the ben is elongated in N-S direction and is limited eastwards palaeontological study of the fishes was published by by a major West Pirin fault of N-S orientation. The Gaudant and Vatsev (2003). Brezhani Graben is about 20 km long and 3 to 5 km wide. The “Pirin” Mine had been open for working a coal Its Cenozoic sedimentary filling, which is Oligocene to seam, 30 m thick, which constitutes the lower part of the Pliocene in age, is 1500 m thick (Vatsev, 1984, 1991). It Rupelian Goreshtitsa Formation (Vatsev, 1984). The coal is subdivided into six formations which, in descending seam is overlaid by fossiliferous bituminous argillites order, are as follow (Fig. 2): (shales) which yielded lower vertebrates: cyprinid fishes (Protothymallus pirinensis Gaudant), anuran and poorly Mechkul Member of the Kalimantsi preserved urodels or squamates (Gaudant and Vatsev, Formation (Vatsev, 1991) 2003). The anuran, which had been first determined as Rana temporaria temporaria by Stefanov (1951), actu- The formation is 400 to 500 m thick and is represented ally belongs to the genus Palaeobatrachus Tschudi. by fluviatile cobble and pebble polylithoclastic conglom- The studied material is housed in the Museum of erates of marble, gneiss, and granite. In its middle part, Geology and Paleontology, University of Mining and lenses of coarse-grained arkosic sandstones are interca- Geology, Sofia (UMG, MGP). lated, whereas granite-gneiss-marble breccia-conglom-

97 Fig. 1. Geological map of the Brezhani Graben (after Vatsev, 1984) 1. Mechkul Member of the Kalimantsi Formation: fluviatile cobble and pebble conglomerates (Pliocene); 2. Dermiritsa Formation: fluviatile cobble and pebble conglomerates (Upper Aquitanian to Lower Burdigalian); 3. Luleva Formation: dark argilites, bituminous sandy argillites, siltstones and sandstones (Aquitanian); 4. Rakitna Formation: sandstones and fluviatile cobble and pebble conglomerates (Chattian); 5. Goreshtitsa Formation: bituminous shales and coal, fossiliferous sandy bituminous argilites, siltstones and sandstones (Rupelian to Lower Chattian); 6. Kachova Formation: conglomeratic breccia, boulder, cobble and and pebble conglomerates and sandstones (Lower Rupelian); 7. Basement: Proterozoic gneisses and marbles and Palaeozoic and Mesozoic granites; 8. fault; 9. stratigraphic boundary: a) normal; b) transgressive; 10. local- ity of fossil fishes and amphibians in the “Pirin” Mine, north of the Brezhani village; SB. Neogene clastic rocks of the neigh- bouring Simitli Graben.

m of clayey sandstones, and sandy dark argillites, the lat- ter including two seams of bituminous coal, 0.3 to 1.5 m thick. Above, there are about 70 m of bituminous sandy or silty argillites, clayey siltstones, and fine-grained sandstones. Its upper part consists of about 60–70 m of sandy argillite showing intercalations of fine-grained sandstone beds and pebble conglomerates. The bituminous argillites of the Luleva Formation represent the second stage of the cyclic development of lacustrine sedimentation in the Brezhani Graben. In the sandy bituminous argillites of the lower and middle parts of the Luleva Formation, a fossil flora is preserved. It is composed of Acer angustilobum Heer, A. palaeosaccharium Stur, Quercus mediterranea Ung. and Q. zoroastrum Ung. (Vatsev, 1984). According to information provided by Adriana Petkova, this thermo- philic flora is probably Chattian in age, although some erates are present in its lower part. In the southern part of its components may suggest a transition towards the of the graben, the Mechkul Member of the Kalimantsi Early Miocene. The middle part of the Luleva Formation Formation lies unconformably on the Dermiritsa and has also yielded the cyprinid fish Palaeoleuciscus ele- Luleva formations or on the metamorphic and granitic gans Gaudant. The genus Palaeoleuciscus is unknown basement. The age of the Mechkul Member is probably before the Early Miocene (Gaudant and Vatsev, 2003). Early Pliocene, Dacian (Vatsev, 1991). Consequently, the Luleva Formation is either latest Chattian or, more probably, its main part is Aquitanian Dermiritsa Formation (Vatsev, 1984) (Upper Egerian) in age.

The thickness exceeds 120 m. This formation consists of Rakitna Formation (Vatsev, 1984) fluviatile cobble and pebble polylithoclastic marble-gneiss- granite conglomerates and of arkosic sandstones which It consists of about 400-450 m of sandstones, sandy argil- are supposed to be late Aquitanian to early Burdigalian lites and polylithoclastic (marble, gneiss, granite) fluvia- (late Egerian to Eggenburgian in terms of the Central tile pebble and cobble conglomerates. The upper part of Paratethyan stages) in age (Gaudant and Vatsev, 2003). the formation consists of rather coarse-grained sandstones which include lenses of conglomerates. According to its Luleva Formation (Vatsev, 1984) position between the Rupelian Goreshtitsa Formation and the latest Chattian to Aquitanian Luleva Formation, This formation, which is about 150 m thick, may be sub- a Chattian (early to middle Egerian) age is likely for the divided into three parts. Its basal part comprises about 8 Rakitna Formation (Vatsev, 1984).

98 Fig. 2. Schematic geological section of the Brezhani Graben Cenozoic filling (after Gaudant and Vatsev, 2003, modified) 1. Holocene clastic sediments; 2a. coal; 2b. bituminous shales; 3a. sandy and silty argillites; 3b. argillites; 4a. coarse-grained sandstones; 4b. medium- and fine-grained sandstones; 5a. cobble conglomerate; 5b. pebble conglomerate; 6a. breccia-conglomerate; 6b. boulder conglomerate; 7. Palaeozoic and Mesozoic granites; 8. Proterozoic gneiss and marble; 9. Oligocene spores and pollen grains; 10a. Oligocene macroflora; 10b. Oligo-Miocene macroflora; 11. fossil fishes; 12. fossil frog; 13. SB – sequence boundary. Aquit. = Aquitanian; Burd. = Burdigalian; Egg. = Eggenburgian.

Goreshtitsa Formation (Vatsev, 1984) marev. Palamarev (1967) identified about 133 species; among them the following indicate an Oligocene This Formation, which is about 100 m thick, is lying con- age: Podocarpus eocenica Ung., Dryophyllum furcin- formably on the Kachova Formation. It begins by a seam erve (Rossm.) Schmalh., “Banksia” helvetica Heer (?), of bituminous coal, the so-called Brezhani coal seam, “Protea” lingulata Heer Ett. (?), “Grevillea” haerin which is a stratigraphic benchmark and was worked in giana Ett. (?), Symplocos brezanii Palam., Sterculia the “Pirin” mine near the village of Brezhani. Above (Brachychiton) labrusca Ung., Pimelea crassipes Heer, the coal seam, there are 70 m of sandy and bituminous Cunonia formosa Frieder., Callicoma microphylla Ett., argillites (shales) with intercalations of thin-bedded silt- Hydrangea palaeopirinica Palam., Caesalpinia haid- stones, fine-grained sandstones and clayey sediments of ingeri Ett., Eucalyptus oceanica Ung., Acacia dianae lacustrine and fluviatile deltaic origin. The bituminous Ett., Mastixia meyeri Kirchh., “Pisonia” eocenica Ett. argillites are fossiliferous. They have yielded macroflo- This subtropical flora clearly differs from the thermophil- ra, gastropods, bivalvians, fishes, previously studied by ic flora of the Luleva Formation. Gaudant and Vatsev (2003), and amphibians. According to the macroflora (Palamarev, 1967) and The fossil macroflora was studied by Palamarev the palynological analysis made by Černjavska (1977), (1967), and an additional material, newly collected by the age of the Goreshtitsa Formation is Rupelian to early M. Vatsev was examined by A. Petkova and E. Pala Chattian. Moreover, the occurrence of the cyprinid fish

99 genus Protothymallus Laube in the bituminous argillites Luleva and Dermiritsa formations. In these rather simi- is indicative of a Rupelian (Early Kiscellian) age, as the lar sedimentary cycles, the sediments of the initial trans- type species of this genus has been identified in several gressive phase are represented by fluviatile conglomer- Oligocene fossiliferous localities in the Czech Republic ates and sandstones. The second transgressive phase is which are older than 30 Ma (Gaudant, 2009). Zaharieva- characterized by palustrine coal argillites and bituminous Kovacheva (1950) noted the occurrence, in the bitumi- coal in the basal part, mainly followed by lacustrine bi- nous shales, of fossil cyprinids that had been wrongly at- tuminous and sandy argillites and also by deltaic and flu- tributed by Weiler to the Miocene species Barbus stein- viatile sandstones. In the upper regressive phase of both heimensis Quenstedt. cycles, deltaic and fluviatile sandstones, sandy argillites, and conglomerates are predominant. Kachova Formation (Vatsev, 1984) Finally, the sediments of the Metchkul Member of the Kalimantsi Formation belong to the upper part of a Late The thickness is 350-400 m. The basal part of the forma- Miocene-Pliocene sedimentary cycle, which is fully tion consists of conglomeratic breccia and conglomer- developed more to the South, in the Sandanski Graben ates of gneiss and marble cobbles and pebbles, includ- (Kojumdgieva et al., 1982). ing granite in its upper part, and alternating with more or less coarse-grained sandstones. Above, there are arkosic sandstones alternating with siltstones in which the occur- SYSTEMATIC PART (J. G.) rence of several thin coal layers is indicative of palustrine Family Palaeobatrachidae Cope, 1865 conditions, although the bulk of the Formation is of flu- Genus Palaeobatrachus Tschudi, 1839 viatile origin. The age of the Kachova Formation is prob- P. cf. grandipes (Giebel, 1851) ably early Rupelian (Early Kiscellian) (Vatsev, 1984). (Figs 3–4)

Identification of sedimentary cycles Several skeletons of adult Palaeobatrachus were collected in the “Pirin” opencast mine, north of the Brezhani The sequences of the Kachova and Goreshtitsa forma- village. They are from the bituminous argillites of the tions build up the Rupelian transgressive-regressive sedi- middle part of the Goreshtitsa Formation. mentary cycle. The second cycle, which is Chattian to The best preserved specimen (UMG, MGP 2216/2217) Aquitanian or early Burdigalian in age (Egerian to Early shows its dorsal and ventral surfaces (Fig. 3). Its main Eggenburgian), includes the sediments of the Rakitna, measurements (in mm) are:

Fig. 3. Palaeobatrachus cf. grandipes (Giebel). General view of specimens UMG, MGP 2216/2217 (part and counterpart), kept in the Museum of Geology and Paleontology, University of Mining and Geology, Sofia (M. Vatsev’s collection) A. Dorsal view B. Ventral view

100 Total length of body (up to the caudal part of ischia): 70 of the metacarpals, their length reacheing 83% of that Distance to the hind part of the sacral vertebra: 47 of the antebrachium. The ratio antebrachium/humerus Length of urostyle: 15 equals 0.75. The hand has four fingers. The phalangeal Length of humerus: 20 formula is unknown. Length of ulna: 15 The synsacrum of specimen UMG, MGP 2216/2217 Length of the third metacarpal: 12.5 could be rather well observed. The large left sacral Length of femur: 31.5 process of the ninth vertebra is more or less axe-shaped. Length of tibio-fibula: 29 Its posterior outline is concave. It is uncertain if the Length of calcaneum: 14 seventh vertebra bears expanded transversal processes. Length of the fourth metatarsal: 12 Although its hindpart is not visible, the urostyle looks The dorsal side of the head (Fig. 3A) is damaged, so rather broad. that the shape of the frontal is unknown. On the coun- Two components of the pelvic girdle are observed terpart (Fig. 3B), the oral processes of the maxillary and on specimen UMG, MGP 2216/2217: the ischium and of the premaxillary are visible. Eight conical teeth are the long, gently curved, ilium which articulates with the exposed on the maxillary and several are still present on synsacrum. The ilium is characterized by a low and elon- the premaxillary. The sphenethmoid is rather elongate; gate tuber superius, a reduced tabular area and a shallow its antero-lateral processes are slghtly developed. The groove on the lateral face of the shaft. parasphenoid is relatively narrow. The shape of its ante- The posterior limbs are characterized by their great rior part is unknown. size as shown by the femur (their length representing The vertebral column of this specimen is also imper- 45% of the total body length) and also by the cruris. The fectly preserved. However, nine procœlous vertebrae are ratio cruris length/femur length reaches 0.92. The tarsus visible on another skeleton (UMG, MGP 2218). comprises two distinct bones: the tibiale and the fibulare, The anatomy of the scapular girdle is unknown, which are not fused distally. A prehallux is present. The except for the scapula which is not much elongated phalangeal formula is unknown. transversally. Four palaeobatrachid tadpoles have also been collect- The forelimbs are characterized by the fusion of the ed in the “Pirin” Mine. For example, the specimen UMG, radius and ulna in the antebrachium and by the great size MGP 2219 (Fig. 4), which is 26 mm long, shows the right and left components of the frontoparietal and the proot- ics; in the middle part, a typically elongate parasphenoid, lacking lateral processes, is visible. The three other tadpoles, which are of more or less similar size (length rang- ing from 23 to 33 mm), are imperfectly preserved. Two of them are exposed in ventral view.

Discussion

Although the skeletons of anurans from the “Pirin” Mine are not excellently preserved, they clearly belong to the family Palaeobatrachidae, as shown by the great development of their hind limbs. More precisely, their rather great size, the morphology of their synsacrum, in which the sacral processes of the ninth vertebra are predominant, and their rather massive urostyle, all lead one to consider that they have a direct relationship to the species P. grandipes. This find is one of the oldest occurrences of this species which was considered by Sanchiz (1998) as being known from localities close to the Oligocene- Miocene boundary (mammal-zone MN 0) and from the Early Miocene (Agenian). However, Smith (2003) reported later that it was already present in the Early Oligocene of Belgium.

Fig. 4. Palaeobatrachus cf. grandipes (Giebel). Tadpole. Specimen UMG, MGP 2220, kept in,the Museum of Geology and Paleontology, University of Mining and Geology, Sofia (M. Vatsev’s collection)

101 It is interesting to note that the palaeobatrachids Bohemia, Czech Republic, and from Saxony, Germany. from the “Pirin” Mine have been found in association Its occurrence in the Rupelian (late Kiscellian) of the with cyprinid fishes. This suggests that they were nor- “Pirin” Mine shows that contrary to the Wuttke’s et al. mally swimming in the palaeolake of Brezhani, together (2012) opinion, the distributional area of the palaeobatra- with the fishes. This ecological behaviour is in agree- chids included already South-Eastern Europe at that time. ment with Špinar’s (1972) opinion who considered that Our find in Bulgaria confirms the occurrence of disartic- “Palaeobatrachids were swimming frogs living perma- ulated palaeobatrachids bones in the Early Oligocene of nently in water throughout their life”. Western Romania (Venczel et al., 2012).

Stratigraphical and biogeographical Conclusion distribution of European palaeobatrachids The find of articulated skeletons of Palaeobatrachus The find of palaeobatrachids in the Oligocene of south- grandipes (Giebel), together with skeletons of cyprinid west Bulgaria extends the geographical distribution of this fishes in the Lower Oligocene of the Brezhani Graben, family to South-East Europe at that time. Precedently, it brings to light an additional evidence that palaeobat- was mainly known from the Upper Oligocene of Bohemia, rachids were swimming anurans living in lacustrine Czech Republic: Bechlejovice, Markvartice and Suletice, environments rather than in swampy areas, as are do- near Litomerice (Špinar, 1972); from the Palaeocene to ing the recent frogs. It confirms the co-occurrence of Middle Miocene of France: Upper Palaeocene of Cernay, palaeobatrachids and cyprinid fishes already made in near Reims, Lower Miocene of Laugnac, Lot-et-Garonne, Germany in the Early Oligocene of Seifhennersdorf and Middle Miocene of Sansan, Gers (Vergnaud-Grazzini (Walther, 1957; Böhme, 2007), in the Late Oligocene and Hoffstetter, 1972); from the Early Oligocene of of the Siebengebirge (Martin, 1989; Wuttke, 1989), of Hoogbutsel and Hoeleden, Flemish Brabant, Belgium Enspel (Böhme, 2000; Wuttke and Poschmann, 2010) (Smith, 2003); from the Oligocene of Jura, Switzerland and Burgbrohl (Wolterstorff, 1929; Gaudant, 2007). (Gaudant, 1979); from the Middle Eocene and Oligocene of Germany: Messel (Wuttke, 1988), Sieblos, Rhön (von Meyer, 1859-1861), Orsberg und Rott, Siebengebirge Acknowledgements (von Meyer, 1859–1861; Wolterstorff, 1885, 1886; Wuttke, 1989), Burgbrohl, Eifel (Wolterstorff, 1929), The authors are indebted to Dr Jean-Claude Rage, Paris, Enspel (Roček and Wuttke, 2010; Wuttke and Poschmann, for the helpful advices. They also thank Adriana Petkova, 2010), Oberleichtersbach, Bavaria (Böhme, 2008) and Sofia, who has provided information on the character- Seifhennersdorf, Saxony (Walther, 1957); and also from istic taxa of the fossil flora from the Brezhani graben. the Upper Miocene (Vallesian) of Hungary: Rudabánya Iskra Lakova and an anonymous reviewer have helped in (Roček, 2005). improving the original manuscript. The photographs are In particular, the species P. grandipes (Giebel) was made by Denis Serrette, Paris, and the illustrations – by known only from the Flemish Brabant, Belgium, from Joël Dyon, Paris.

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