ISSN 0031-0301, Paleontological Journal, 2009, Vol. 43, No. 2, pp. 197–200. © Pleiades Publishing, Ltd., 2009. Original Russian Text © S.V. Moloshnikov, 2009, published in Paleontologicheskii Zhurnal, 2009, No. 2, pp. 76–78.
Oredezhosteus, a New Psammosteid Genus (Heterostraci, Psammosteiformes) from the Lower Frasnian (Upper Devonian) of the Main Devonian Field S. V. Moloshnikov Earth Science Museum, Moscow State University, Moscow, 119899 Russia e-mail:
[email protected] Received April 23, 2008
Abstract—A new psammosteid, Oredezhosteus kuleshovi gen. et sp. nov., from the Amata Regional Stage (Lower Frasnian) of the Leningrad Region is described. In addition, Psammosteus livonicus Obruchev from beds of the same age from Latvia is included in the new genus. The major diagnostic characters distinguishing Oredezhosteus gen. nov. from Psammosteus Agassiz are the large rounded striated tubercles, which cover more than half width of the branchials, and the long base of the branchial plates. DOI: 10.1134/S0031030109020117 Key words: Agnatha, Psammosteiformes, Upper Devonian, Frasnian, Main Devonian Field, Russia.
INTRODUCTION Obruchev (Obruchev and Mark-Kurik, 1965) described Psammosteus livonicus Obruchev from the Amata beds (Lower Frasnian) of the Baltic Region. He described branchial plates and fulcral scales of this species and indicated that P. livonicus sharply differs from all other species of Psammosteus Agassiz in the sculpture and is most similar to Psammolepis venyukovi Obruchev, 1965 (Obruchev and Mark-Kurik, 1965, p. 238); this suggests that this species has an uncertain position among psammosteids. Subsequently, MarkKurik (1968) described a dorsal plate with a similar unusual sculpture and assigned it to P. livonicus Obr. In 2000, M.Yu. Kuleshov found branchials and fulcral scales of a new psammosteid species in the Amata beds near the village of Yam-Tesovo on the Oredezh River (Leningrad Region). It shares a number of morphological features with Psammosteus livonicus Obruchev and differs from it in the simpler dentin tubercles. The unusual sculpture of the bone surface, which consists of relatively large, high, and symmetrical (circular in cross section) tubercles, distinguishes these two species from all congeners. In addition, an almost complete branchial plate of the new species, which was found near the village of Yam-Tesovo, has a long base and its ventral side is almost completely covered with dentin tubercles, characters unusual for the genus Psammosteus (Obruchev and Mark-Kurik, 1965, p. 216; Tarlo, 1965, p. 114). Based on these characters, it is here proposed to assign the two Amata species to a separate genus, Oredezhosteus gen. nov. To date, the stratigraphic position of the Amata Regional Stage and its analogues (boundary beds between the Middle and Upper Devonian) on the East
Europe Platform has not been established with certainty. In the present study, according to the Resolution… (1990), the Amata Regional Stage is assigned to the Lower Frasnian Substage of the Upper Devonian. The material under study is housed in the Paleontological Institute of the Russian Academy of Sciences, Moscow (PIN), collection no. 1737. SYSTEMATIC PALEONTOLOGY Order Psammosteiformes Family ? Psammosteidae Traquair, 1896 Genus Oredezhosteus Moloshnikov, gen. nov. Psammosteus (part.): Obruchev and Mark-Kurik, 1965, pp. 215– 219; Mark-Kurik, 1968, p. 419.
E t y m o l o g y. From the Oredezh River and the Greek osteon (bone). T y p e s p e c i e s. Psammosteus livonicus Obruchev, 1965; Main Devonian Field; Upper Devonian, Lower Frasnian, Amata Regional Stage. D i a g n o s i s. Branchiale wide, with long base. Dentin tubercles large (1–2 mm in diameter), high, dome-shaped, circular in cross section, covered with thin striae, sometimes with short teeth. Tubercles covering more than half width of dorsal and ventral surfaces of branchiale. Smaller dentin tubercles located between large ones. S p e c i e s c o m p o s i t i o n. In addition to the type species, O. kuleshovi sp. nov. C o m p a r i s o n. The new genus differs from Psammosteus Agassiz in the long base of the branchial plates, the large symmetrical dentin tubercles (in Psammosteus, the dentin tubercles are usually asymmetri-
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MOLOSHNIKOV Plate 13
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E x p l a n a t i o n o f P l a t e 13 Figs. 1–5. Oredezhosteus kuleshovi gen. et sp. nov.: (1) specimen PIN, no. 1737/76, fulcral scale, ×1.7: (1a) internal and (1b) external sides; (2) specimen PIN, no. 1737/76, dentin tubercles of fulcral scale, ×6.5; (3) holotype PIN, no. 1737/74, right branchial, ×1.35: (3a) ventral and (3b) dorsal views; (4, 5) holotype PIN, no. 1737/74, dentin tubercles: (4) dorsal surface of the branchial, ×3; and (5) dorsal side of the proximal part of the branchial, ×6.5. PALEONTOLOGICAL JOURNAL
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Fig. 1. Oredezhosteus gen. nov., right branchial plates: (a) O. livonicus (Obruchev, 1965), holotype PIN, no. 1737/7, ventral view; (b, c) O. kuleshovi sp. nov., holotype PIN, no. 1737/74: (b) ventral and (c) dorsal views.
cal), which sometimes have short simple teeth (in Psammosteus, the teeth are usually long and branching: Obruchev, 1964). In addition, it differs from Psammosteus in the larger sculptured area on the branchiale (in Oredezhosteus, the ventral side is covered with tubercles for more than half of the width; in Psammosteus, the tubercles cover only the distal part). The new genus is similar to Karelosteus Obruchev in the shape of the branchiale and differs from it in the smaller dentin tubercles (almost half as large), which are circular in cross section (in Karelosteus, they are extended) and positioned more loosely. The new genus is similar to Ganosteus Rohon in the shape of the branchial plates and differs in the more densely positioned, smaller tubercles (in Ganosteus, they are up to 5 mm in diameter), and in the short simple teeth on these tubercles. It differs from Psammolepis Agassiz in the larger and higher tubercles and the shorter base of the branchial plates. R e m a r k s. The long base of the branchiale and the large, rounded, symmetrical tubercles not only distinguish the new genus from Psammosteus but also resemble Psammolepis and Ganosteus; therefore, Oredezhosteus gen. nov. is tentatively assigned to the family Psammosteidae Traquair, 1896. Oredezhosteus livonicus (Obruchev, 1965)
Psammosteus livonicus: Obruchev and Mark-Kurik, 1965, p. 238, pl. XCIV, figs. 1–2; Mark-Kurik, 1968, pp. 420, 421, textfig. 11; Novitskaya, 2004, p. 191. PALEONTOLOGICAL JOURNAL
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H o l o t y p e. PIN, no. 1737/7, right branchiale; Latvia, left bank of the Daugava River opposite Pastemuizha; Upper Devonian, Lower Frasnian, Amata Regional Stage. D e s c r i p t i o n (Fig. 1a). The branchial plate is wide and has a relatively long base. Its posterior margin is concave and the lateral margin is convex. The lateral angle is about 50°. The dentin tubercles on the ventral side cover more than half of the plate width. The tubercles are large, conical and dome-shaped, with short teeth that extend to the apex in the shape of distinct ribs; the density of tubercles is on average 8–10 per 1 cm. Some teeth ramify. In the distal part of the branchiale, dentin tubercles form transverse rows. M e a s u r e m e n t s, mm. Branchiale, holotype PIN, no. 1737/7: length, 26; width, ca. 48; thickness, up to 2. C o m p a r i s o n. O. livonicus differs from O. kuleshovi sp. nov. in the shorter base of the branchiale, the smaller lateral angle of this bone, and the larger dentin tubercles. In addition, the ribs on dentin tubercles of O. livonicus reach their apices, while, in O. kuleshovi sp. nov., they cover only their lower half. In O. livonicus, the dentin tubercles in the distal part of the dorsal side of the branchiale form transverse rows; O. kuleshovi lacks these rows. M a t e r i a l. In addition to the holotype, one branchial plate and one fulcral scale from the collection of D.V. Obruchev.
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MOLOSHNIKOV Oredezhosteus kuleshovi Moloshnikov, sp. nov. Plate 13, figs. 1–5
E t y m o l o g y. The species is named in honor of M.Yu. Kuleshov, who found remains of this species. H o l o t y p e. PIN, no. 1737/74, right branchiale; Leningrad Region, River Oredezh, village of Yam-Tesovo; Upper Devonian, Lower Frasnian, Amata Regional Stage. D e s c r i p t i o n (Figs. 1b, 1c). The right branchial plate is dorsally convex, with a long base. Its posterior margin is concave and the lateral margin is convex. The lateral angle is approximately 60°. About two-thirds of the dorsal surface is covered with dentin tubercles, the ventral surface is almost completely covered with tubercles. This means that the proximal part of the bone was not covered with tesserae. The dentin tubercles are large, 1–1.5 mm in diameter (up to 10 per 1 cm), domeshaped, circular in cross section, have short, nonramified teeth (Pl. 13, figs. 4, 5). Only the lower part of tubercles is covered with thin ribs, which terminate short of the apex. Small tubercles are located between large ones. The fulcral scales are relatively wide (Pl. 13, fig. 1), the length-to-width ratio is 2.05. Dentin tubercles on the scales are very similar to those on the branchiale, dome-shaped, ovate in cross section, have short teeth (Pl. 13, fig. 2). Only the lower half of the tubercles is usually covered with ribs. M e a s u r e m e n t s, mm. Branchiale, holotype PIN, no. 1737/74: length, ca. 45; width, 58; thickness, up to 5.6; fragmentary branchiale, specimen PIN, no. 1737/75: thickness, up to 7.5; fulcral scales, specimen PIN, no. 1737/76: length, ca. 35; width, 17. C o m p a r i s o n. See description of O. livonicus (Obruchev, 1965).
M a t e r i a l. In addition to the holotype, one fragment of the branchial plate and one fulcral scale from the type locality. ACKNOWLEDGMENTS I am grateful to M.Yu. Kuleshov (Zoological Institute, Russian Academy of Sciences, St. Petersburg) for providing me with psammosteid specimens from the Amata beds of the Leningrad Region. REFERENCES 1. E. Mark-Kurik, “New Finds of Psammosteids (Heterostraci) in the Devonian of Estonia and Latvia,” Izv. Akad. Nauk Est. SSR 17 (4), 410–424 (1968). 2. L. I. Novitskaya, “The Subclass Heterostraci,” in Fossil Vertebrates of Russia and Adjacent Countries: Agnathans and Ancient Fishes: Handbook for Paleontologists, Biologists, and Geologists, Ed. by L. I. Novitskaya (GEOS, Moscow, 2004), pp. 69–207 [in Russian]. 3. D. V. Obruchev, “Subclass Heterostraci (Pteraspides),” in Fundamentals of Paleontology: Agnathans and Fishes, Ed. by D. V. Obruchev (Nauka, Moscow, 1964), pp. 45–82 [in Russian]. 4. D. V. Obruchev and E. Yu. Mark-Kurik, Psammosteids (Agnatha, Psammosteidae) from the Devonian of the Soviet Union (Inst. Geol. Akad. Nauk Est. SSR, Tallinn, 1965) [in Russian]. 5. Resolution of the Interdepartmental Regional Stratigraphic Meeting on the Middle and Upper Paleozoic of the Russian Platform, with Regional Stratigraphical Schemes, Leningrad, 1988: Devonian System (Leningrad, 1990) [in Russian]. 6. L. B. Tarlo (Halstead), “Psammosteiformes (Agnatha)— A Review with Descriptions of New Material from the Lower Devonian of Poland: Part II: Systematics,” Palaeontol. Polon., No. 15, 1–168 (1965).
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