Devonian acanthodians from Severnaya Zemlya Archipelago (Russia) Juozas VALIUKEVIČIUS Institute of Geology and Geography, T. Ševčenkos 13, LT 2600 Vilnius (Lithuania) [email protected] Valiukevičius J. 2003. — Devonian acanthodians from Severnaya Zemlya Archipelago 406 (Russia). Geodiversitas 25 (1) : 131-204. ABSTRACT Acanthodians from the stratigraphic interval of late Pridoli (Late Silurian) to Givetian (Middle Devonian) are studied. Based on 48 acanthodian taxa, bio- stratigraphic zones are established within the late Pridoli (Poracanthodes punctatus Zone, Krasnaya Bukhta Formation) and Lochkovian (Nostolepis minima Zone), the latter divided into two subzones: Poracanthodes menneri (Severnaya Zemlya Formation) and Diplacanthus poltnigi n. sp. (Pod”emnaya Formation). Two more biostratigraphic units are charac- terised by index species, but they have no acanthodian-based boundaries (separated by intervals without effective acanthodian characteristics). These are beds with Watsonacanthus costatus n. sp. typical for the Emsian Rusanov and lower Al’banov formations, and Eifelian? or Eifelian/Givetian? beds with Diplacanthus solidus n. sp. (Vstrechnaya Formation). Five new genera and 14 new species are described. They are based on articulated specimens from the topmost Severnaya Zemlya Formation (Acritolepis ushakovi n. gen., n. sp., A. urvantsevi n. gen., n. sp., Acanthacanthus ornatus n. gen., KEY WORDS Acanthodii, n. sp., Nostolepis decora n. sp., N. fragilis n. sp., Acanthopora transitans n. gen., Lower to Middle Devonian, n. sp. and Acanthospina irregulare n. gen., n. sp.) or on isolated scales identi- Severnaya Zemlya Archipelago, fied from different formations (Nostolepis timanica n. sp., N. watsoni n. sp., Russia, new genera, Watsonacanthus costatus n. sp., Diplacanthus poltnigi n. sp., D. solidus n. sp., new species. Gomphonchus nordicus n. sp. and Arcticacanthus bicostatus n. gen., n. sp.). GEODIVERSITAS • 2003 • 25 (1) © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com 131 Valiukevičius J. RÉSUMÉ Les acanthodiens dévoniens de l’archipel de Severnaya Zemlya (Russie). Les acanthodiens présents dans l’intervalle stratigraphique du Pridoli supé- rieur (Silurien supérieur) au Givétien (Dévonien moyen) sont étudiés. À partir de 48 taxons d’acanthodiens, les zones stratigraphiques du Pridoli supérieur (Zone à Poracanthodes punctatus, Formation de Krasnaya Bukhta) et du Lochkovien (Zone à Nostolepis minima) ont été établies. Cette dernière zone est divisée en deux sous-zones : Poracanthodes menneri (Formation de Severnaya Zemlya) et Diplacanthus poltnigi n. sp. (Formation de Pod”emnaya). Deux autres unités biostratigraphiques ont été définies par des espèces index : l’unité à Watsonacanthus costatus n. sp. rattachée aux for- mations emsiennes de Rusanov et de l’Al’banov inférieur et l’unité à Diplacanthus solidus n. sp. (Formation de Vstrechnaya) d’âge Eifélien ? ou Eifélien/Givétien ? Ces unités sont délimitées par des intervalles non définis car ne présentant pas d’acanthodiens stratigraphiquement caractéristiques. Cinq nouveaux genres et 14 nouvelles espèces sont décrits. Ils sont basés sur des spécimens articulés du sommet de la Formation de Severnaya Zemlya (Acritolepis urvantsevi n. gen., n. sp., A. ushakovi n. gen., n. sp., Acanthacanthus ornatus n. gen., n. sp., Nostolepis decora n. sp., N. fragilis MOTS CLÉS Acanthodii, n. sp., Acanthopora transitans n. gen., n. sp. et Acanthospina irregulare n. gen., Dévonien inférieur et moyen, n. sp.) ou sur des écailles isolées récoltées dans différentes formations archipel de Severnaya Zemlya, (Nostolepis timanica n. sp., N. watsoni n. sp., Watsonacanthus costatus n. sp., Russie, nouveaux genres, Diplacanthus poltnigi n. sp., D. solidus n. sp., Gomphonchus nordicus n. sp. et nouvelles espèces. Arcticacanthus bicostatus n. gen., n. sp.). INTRODUCTION Komsomolets Island in 1979, have also been included in this study. The end of the 1970s was the most successful The uninterrupted bed-by-bed sampling of period of field sampling of Severnaya Zemlya Lower and Middle Devonian rock sequence, acanthodians. Detail field work on the October mainly represented by Old Red Sandstone Revolution Island in 1978 allowed the discovery facies, was impossible because of the hardly of the first Early Devonian articulated acantho- cemented, siliceous and mainly non-carbonate dians ever known from Arctic Russia and until rocks. Therefore acanthodians are restricted to now they remain the only elements for biogeo- selected stratigraphic levels. Microremains of graphical correlation with other regions. Rock other fish groups could also be recovered only samples for microremains were collected in from dissoluble rocks. Thus large or smaller 1978. Acetic acid dissolution of these samples parts of several formations did not deliver any has enriched the collection of acanthodian information on acanthodians; this concerns the microremains (scales and spine fragments) Givetian Vatutin Formation, the lower part of referred to in this article. Apart from this mate- Vstrechnaya Formation (Eifelian?) and the rial, samples collected by E. Kachanov and upper Al’banov Subformation (Emsian). M. Gagiev (Magadan, Russia), on Pioneer Island Despite a sufficiently detail sampling, the lower in 1976, and by E. Mark-Kurik (Tallinn, Estonia) part of Pod’’emnaya Formation (Lochkovian) and A. Khapilin (St. Petersburg, Russia), on has yielded only three transitional acanthodian 132 GEODIVERSITAS • 2003 • 25 (1) Devonian acanthodians from Severnaya Zemlya species. Thus with biostratigraphic respect, it is Order CLIMATIIFORMES Berg, 1940 conventionally joined with its well characterised Suborder and Family indet. upper part. The absence of acanthodian-based Genus Acritolepis n. gen. biostratigraphic unit for the Spokojnaya Formation (Pragian), is due to similar reasons. TYPE SPECIES.— Acritolepis ushakovi n. gen., n. sp. The gaps in the acanthodian vertical distribution ETYMOLOGY. — From Acritos (Greek): stumbling, reveal occurrences of beds with index species mixed; and lepis (Greek): scale. but without acanthodian-based joint bound- OTHER SPECIES INCLUDED.— Acritolepis urvantsevi aries. n. gen., n. sp. Denser nearly bed-by-bed sampling for AGE. — Early Devonian, early Lochkovian. microremains has been done within the Eifelian formations in order to establish an assemblage- DIAGNOSIS. — Small-sized moderately deep-bodied climatiid with lowly erected longitudinally six-ribbed based correlation with well documented related dorsal spines, long thick-walled eight-ribbed pectoral facies of the Baltic basin. These intervals con- spines and slender cylindrical scapula. Spines com- cern the outcrop 5, beds 48-153 and outcrop 7, posed of highly vascularised bone and mesodentine. beds 2-18 along the Matusevich River (58 sam- Prepectoral spines, tectal plates of the shoulder girdle region and jawbones with teeth are present. Body ples in the Al’banov-Vstrechnaya-Vatutin for- scale crowns flattened and elongated with short ante- mations) and several levels at the Ushakov River rior ridges, composed dominantly of Stranggewebe (26 samples from the outcrops 25, 26 and 27 in and simple mesodentine. Al’banov-Vstrechnaya formations). An incomplete stratigraphic distribution of taxa DISCUSSION did not allow us to establish an acanthodian zonal The taxonomic position of Acritolepis n. gen. scheme for the entire time interval under study. among Climatiiformes is hardly recognisable. Zonation is acceptable only for the Pridoli (Late Fin spines in most representative Climatiidae Silurian) and the Early Devonian (Lochkovian). are short and stout, sometimes robust, mainly Pridolian acanthodians are included for compari- ornamented by beaded, nodose or tuberculated son with the earliest Devonian assemblage and ribs, rarely with distal denticles. Smooth, certainty of acanthodian-based regional bound- moderately slender ribs are only present in ary of Pridoli/Lochkovian. Euthacanthus Powrie, 1864 (Denison 1979). The presence of two dorsal fin spines, proposed by Gagnier & Wilson (1995, 1996b) in the precise SYSTEMATICS diagnosis of the order, remains almost the only feature occurring in Acritolepis n. gen., but their Only the new acanthodian taxa are described. shape and insertion points are only comparable For the known species photographic illustra- to Vernicomacanthus Miles, 1973 (long anterior tions are provided and their stratigraphic distri- dorsal inserted behind the pectorals and poste- bution is summarised in Tables 2 and 3. rior dorsal inserted behind pelvic spine). The An exception is made for the poracanthodids, posterior dorsal spine is longer than the anterior due to difficulties to identify their species, since one, a feature mentioned in Brachyacanthus the Severnaya Zemlya examples demonstrate Egerton, 1860, Lupopsyrus Bernacsek & several differences from the published material. Dineley, 1977 and Brochoadmones Bernacsek & Short descriptions and discussions on morpho- Dineley, 1977, which essentially differ by other logic and histological characters are summarised peculiarities. The first two genera are charac- in Remarks. terised like Acritolepis n. gen. by a position of The whole collection is stored in the Museum of the posterior dorsal spine opposite the anal. The Lithuanian Institute of Geology and Geography new genus is especially distant from most (LIG) in Vilnius, under catalogue number 35. Climatiidae by lack of intermediate spines. GEODIVERSITAS • 2003 • 25 (1) 133 Valiukevičius