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42 ADVANCES IN PALAEOICHTHYOLOGY this situation it is surprising that none of the dorsal plates of Obruchevia show any indication of the presence of the sensory canal system. Halstead Tarlo (1964) placed Obruchevia together with Traquairosteus in the Family Obrucheviidae, an arrangement that we agree with here. It is also clear that the new genus Perscheia should be included within this family. Higher level phylogenetic relationships are poorly understood, as no attempt has been made to assess relationships within the Psammosteiformes since the study by Halstead Tarlo (1964). This study was flawed somewhat by the inclusion of a number of early species that are now not considered to be psammosteids, such as Tesseraspis, Corvaspis, and Psephaspis. Halstead Tarlo used a variety of features such as the type of ornamentation, and the shape of the branchial and ventral plates to show that advanced psammosteids derive from Guerichosteus, from the Emsian of central Poland, which subsequently gave rise to two lineages. In one the posterior notch in the ventral plate was deepened and widened, and the branchial plate became broad and triangular (Pycnolepis, Pycnosteus). In the other lineage the posterior ventral notch was progressively eliminated, and the branchial plates became greatly shortened and broadened, forming spine-like plates in some forms (Psammosteus). Obruchevia and Traquairosteus were very incompletely known at the time Halstead Tarlo attempted his analysis of phylogeny; however, he placed them in a tentative relationship with psammolepids based on the fact that the branchial plates were strongly downturned, a feature that is present to a much lesser degree in the psammolepids, and despite the fact that the branchial plates of Obruchevia are long and narrow, not short and broad. The new information presented here shows that both Obruchevia and Perscheia had a ventral plate in which a well-developed posterior notch was present, therefore indicating that the obrucheviids are more likely to be connected to the group including Pycnolepis, Pycnosteus, and Tartuosteus in which this is a major feature. However, until a modern phylogenetic analysis of the Psammosteiformes has been carried out, a study that is beyond the scope of this paper, no firm conclusion can be reached as to the relationship of the obrucheviids. Acknowledgments. - We would like to thank Hans Arne Nakrem of the Geologisk Museum, Oslo and Ervīns Lukševičs of the Natural History Museum, Riga for arranging the loan of specimens in their collections, and Oleg Lebedev, Moscow, for photographs of the branchial plates of Obruchevia. D.K.E. acknowledges the receipt of a COBASE grant that supported reciprocal visits with E. M.-K., and support from the Academy of Natural Sciences, Philadelphia for visits to the collections. E. M.-K. is grateful to the Estonian Science Foundation (Grant No.5275) and IGCP Project 491 for financial help. This work is also supported by the following grants to E.B.D.: National Science Foundation Grant No. 0207721 and National Geographic Society Committee for Research and Exploration Grant No. 7223-02. Photographs of the Latvian specimens and the Perscheia thin sections were made by G. Baranov, Tallinn. We particularly thank S. Swift, Flagstaff, who photographed the Canadian material and assembled the photographic figures, and Drs. A. Blieck (Lille), R. Thorsteinsson (Calgary), and M. Wilson (Edmonton) who provided constructive criticism of the manuscript.
D.K. Elliott, E. Mark-Kurik, E.B. Daeschler. A revision of Obruchevia 43 References Berg L. S. 1955. Classification of fishes, both Recent and fossil. Travaux de l’Institut Zoologique, Academie des Sciences de l’Union des Republiques Soviétiques Socialistes, 20: 1-286. [in Russian] Blieck A., Elliott D. K., Gagnier P-Y. 1991. Some questions concerning the phylogenetic relationships of heterostracans, Ordovician to Devonian jawless vertebrates. p.1-17, In M-M. Chang, Y-H. Liu, & G-R. Zhang (eds.) Early Vertebrates and Related Problems of Evolutionary Biology. Science Press, Beijing:1-17. Blieck A., Mark-Kurik E., Märss T. 1988. Biostratigraphical correlations between Siluro-Devonian invertebrate-dominated and vertebrate-dominated sequences: the East Baltic example. In N.J McMillan, A.F. Embry, & D.J. Glass, (eds.). Devonian of the World, 3. Canadian Society of Petroleum Geologists Memoir, 14: 579-587. Elliott D. K. 1984. A new subfamily of the Pteraspididae (Agnatha, Heterostraci) from the upper Silurian and lower Devonian of Arctic Canada. Palaeontology 27:169-197. Elliott D. K., Mark-Kurik E., Daeschler E. 2003. A revision of the obrucheviids (Psammosteidae, Heterostraci) from the Late Devonian of arctic Canada and Russia. In H.-P. Schultze, E. Lukševičs, and D. Unwin (eds.). The Gross Symposium 2: Advances in Paleoichthyology. Ichthyolith Issues Special Publication, 7:21-22. Embry A., Klovan J. E. 1976. The Middle-Upper Devonian Clastic wedge of the Franklinian Geosyncline. Bulletin of Canadian Petroleum Geology 24:485-639. Esin D., Ginter M., Ivanov A., Lebedev O., Luksevics E., Avkhimovich V., Golubtsov V., Petukhova L. 2000. Vertebrate correlation of the Upper Devonian and Lower Carboniferous on the East European Platform. Courier Forschungsinstitute Senckenberg, 223: 341-359. Gross W. 1963. Drepanaspis gemuendenensis Schlüter. Neuuntersuchung. Palaeontographica, 121, A:133-155. Halstead Tarlo L. B. 1962. The classification and evolution of the Heterostraci. Acta Palaeontologica Polonica, 7: 249-290. Halstead Tarlo L. B. 1963. Aspidin: the precursor of bone. Nature, 199 (4888): 46-48. Halstead Tarlo L. B. 1964. Psammosteiformes (Agnatha) - A review with description of new material from the Lower Devonian of Poland. I. General part. Palaeontologica Polonica, 13: 1-135. Halstead Tarlo L. B. 1965. Psammosteiformes (Agnatha) - A review with description of new material from the Lower Devonian of Poland. II. Systematic part. Palaeontologica Polonica, 15: 1-168. Halstead Tarlo 1967a. The tessellated pattern of dermal armour in the Heterostraci. The Journal of the Linnean Society (Zoology), 47 (311): 45-54. Halstead Tarlo L. B. 1967b. Major faunal provinces in the Old Red Sandstone of the Northern Hemisphere. In D. H. Oswald (ed.). International Symposium on the Devonian System, Calgary, 2. Alberta Society of Petroleum Geologists: 1231-1238. Halstead L. B. 1969. The Pattern of Vertebrate Evolution. Oliver & Boyd, Edinburgh: 209 pp. Halstead L. B. 1974. Vertebrate Hard Tissues. Wykeham Publications (London) Ltd, London and Winchester: 179 pp. Harrison J. C., de Freitas T. 1998. Bedrock geology, Helena Island (NTS B and 79A), Bathurst Island Group, District of Franklin, Northwest Territories (Nunavut), Geological Survey of Canada, Open File 3577. Hecker R. F., Obruchev D. V., Filippova M. F. 1935. Deposits of the Main Devonian Field, V- VII. Transactions of the Leningrad Geological, Hydrogeological and Geodetical Trust, Fascicle 9: 1-82. [in Russian, English summary] ICZN. 1964. International Code of Zoological Nomenclature . 2 nd Ed. London. ICZN. 1999. International Code of Zoological Nomenclature . 4 th Ed. London. Janvier P. 1996. Early Vertebrates. Clarendon Press, Oxford: 393 pp. Kiaer J. 1915. Upper Devonian fish remains from Ellesmere Land, with remarks on Drepanaspis. Report of the Second Norwegian Arctic expedition in the “Fram” 1898-1902, 33: 1-72. Lyarskaya L. 1971. New finds of psammosteid remains from the ventoji horizons of Latvia. In A. Grigelis (ed.). Palaeontology and Stratigraphy of the Baltic and the Byelorussia . Mintis, Vilnius: 97-104. [in Russian, English summary]
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Page 9 and 10: Ervīns Lukševičs, Ģirts Stinkul
Page 15 and 16: Olga Afanassieva. Microrelief on th
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Page 47 and 48: C.G.Miller, T. Marss, H. Blom. New
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O.A. Lebedev. A new tetrapod from R
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