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28 ADVANCES IN PALAEOICHTHYOLOGY Fig. 2. Map of the Novgorod area to show the Obruchevia localities and the section of the Prilovat´ Formation at the Luka locality on the Lovat´ River, and the Frasnian biozones and subdivisions in the NW of the East European Platform (modified after Lukševics 2001). Abbreviations: FM, Famennian, GV, Givetian, MDF, Main Devonian Field, the Baltic part. Staraya Russa and Bologoe (to the East), at Cherenchitsy, and about 20 km further upstream. One more locality is known from the Msta River at Polosy northeast of Novgorod. The type locality of Obruchevia (Aspidosteus) is at Kulakova, on the Lovat´ River (Obruchev 1941). In 1958 an expedition led by Prof. D. Obruchev to the Novgorod Region yielded many Obruchevia plates upstream of Luka on the River Lovat´. A large dorsal shield and several branchial plates were excavated, and Halstead Tarlo briefly described the latter in 1965. The Obruchevia collection belonging to the Natural History Museum of Latvia was collected in 1998 and comes from the Peryesy locality (Fig. 2). It includes several fragments of dorsal plates, a large fragment of the right branchial plate and a ventral plate fragment.
D.K. Elliott, E. Mark-Kurik, E.B. Daeschler. A revision of Obruchevia 29 Obruchev (1940) published the description of the Luka section in his paper on the Devonian river delta on the Lovat´ River. In 1958 about 10 m of the section was documented by Elga Mark. The Luka locality (Fig. 2, upper left) is an extensive outcrop, consisting of rather soft terrigenous rocks of the Frasnian Prilovat´ Formation (Fig. 2, lower left). It consists of purple, brown, red or greenish clay, and white, yellow or brownish siltstone and sandstone (Fig. 2, right). Fossil fishes were discovered in a clay bed (IV fish horizon) and three siltstone and/or sandstone beds in the lower part of the section, the II fish horizon being the richest. In both these horizons the same fishes occurred: Obruchevia heckeri, Bothriolepis maxima and the sarcopterygian Platycephalichthys bishoffi. The II horizon yielded an additional psammosteid, Psammosteus falcatus. According to Esin et al. (2000) the above mostly large or very large forms characterize the Snezha-Prilovat´ (or Katleši-Pamušis) interval of the Upper Frasnian of the NW of the East European Platform (Fig. 2, lower left). Psammosteus falcatus and Bothriolepis maxima are Late Frasnian index fossils (Lukševics 2001). The marine basin during the Pamušis (Ogre)-Prilovat´ time was shallow and dominated by clastic sedimentation. The main source area of rich detrital material was situated to the north and northwest in the area occupied by the modern Baltic Shield (Sorokin 1978, p. 236, fig. 50). Obruchevia heckeri (Obruchev, 1936) (Figs. 3-5) Diagnosis. (Modified after Halstead Tarlo, 1965) Dorsal plate thick with wide, shallow re-entrant angle at anterior margin, and marked notch in posterior part of each lateral margin. Ornamentation of smooth, radial grooves and shallow, circular pits. Histological structure of spongy aspidin reinforced by pleromic dentine towards external surface. Branchial plates thin, long and narrow, and bent at right angles so that the lateral part is oriented vertically. Ventral plate thick with a long, posterior median notch. Material. Six branchial plates (PIN 87/9-13; Pl 10/8); three dorsal plate fragments (Pl 10/ 9, 10/11, 10/12); ventral plate fragment (Pl 10/10). Locality. Lovat´ River, near Peryesy and Luka, Novgorod, Region, Russia. Prilovat´ Formation, Upper Devonian, Frasnian. Description. The description of Obruchevia (Aspidosteus) was based on its dorsal plates (Obruchev 1941, pl. I), the other plates only becoming known later. The dorsal plates are very large, notably thick, and cardiform. The length of the holotype (housed in the CNIGR Museum, St. Petersburg, coll. # 1/4680) is 510 mm and the maximum width is 480 mm. The ornament of the external surface of the plates varies: it consists either of radial furrows (Obruchev 1941; pl. I, fig. 1) or of pits or both (Obruchev 1941; pl. I, fig. 2; pl. II, fig. 3). Two fragments from the Riga collection show variations of the ornament (Fig. 3). One specimen (Pl 10/12, Fig. 3B) has strongly developed furrows, but in the other (Pl 10/ 11, Fig. 3A) the furrows are wider, wavy, and more delicate. The dorsal plates appear to have grown by the addition of lateral flanges that developed from the lower surface of the margins. In Pl 10/12 four such flanges can be counted (Fig. 3B). The visceral surface of the fragments has marginal zones, lacking the basal layer, that are 30-50 mm wide.
Page 1 and 2: LATVIJAS UNIVERSITĀTES RAKSTI 679.
Page 3 and 4: LATVIJAS UNIVERSITĀTES RAKSTI 679.
Page 5 and 6: Contents Ervīns Lukševičs and Ģ
Page 7 and 8: ACTA UNIVERSITATIS LATVIENSIS, 2004
Page 9 and 10: Ervīns Lukševičs, Ģirts Stinkul
Page 15 and 16: Olga Afanassieva. Microrelief on th
Page 23 and 24: D.K. Elliott, E. Mark-Kurik, E.B. D
Page 27: D.K. Elliott, E. Mark-Kurik, E.B. D
Page 47 and 48: C.G.Miller, T. Marss, H. Blom. New
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Page 59 and 60: H.-P. Schultze, T. Marss. Revisitin
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ACTA UNIVERSITATIS LATVIENSIS, 2004
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O.A. Lebedev. A new tetrapod from R
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ACTA UNIVERSITATIS LATVIENSIS, 2004
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E. Lukševičs, I. Zupiņš. Sedime
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J. Valiukevičius. Silurian acantho
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V. Pernegre, V. Dupret. Biostratigr
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Ž. Žigaite. New telodont from Tuv
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