A new genus of ptyctodont (Placodermi) from the Late Devonian of Baltic area

he ptyctodont fish first referred to as Chelyophorus pskovensis Obruchev, 1947 from the Early Frasnian (Late Devonian) of Velikaya River, Pskov Region, Russia, is redescribed following the collection of additional materials from the contemporaneous Meeksi Mill outcrop, Estonia; Piskovichi and Snetnaya Gora outcrops, Russia and is here referred to Meeksiella gen. nov. With the exception of an articulated skull roof, the fossils occur as three dimensionally preserved isolated plates, and this has allowed accurate reconstruction of the dermal skeleton. A phylogenetic analysis resolves Meeksiella pskovensis gen. et sp. nov. within a previously recovered cluster of taxa which includes Ctenurella from Europe and Austroptyctodus from Western Australia, demonstrating global distribution of this clade during the Late Devonian

Endoskeletal structure in Cheirolepis (Osteichthyes, Actinopterygii), An early ray-finned fish

As the sister lineage of all other actinopterygians, the Middle to Late Devonian (Eifelian–Frasnian) Cheirolepis occupies a pivotal position in vertebrate phylogeny. Although the dermal skeleton of this taxon has been exhaustively described, very little of its endoskeleton is known, leaving questions of neurocranial and fin evolution in early ray‐finned fishes unresolved. The model for early actinopterygian anatomy has instead been based largely on the Late Devonian (Frasnian) Mimipiscis, preserved in stunning detail from the Gogo Formation of Australia. Here, we present re‐examinations of existing museum specimens through the use of high‐resolution laboratory‐ and synchrotron‐based computed tomography scanning, revealing new details of the neuro‐cranium, hyomandibula and pectoral fin endoskeleton for the Eifelian Cheirolepis trailli. These new data highlight traits considered uncharacteristic of early actinopterygians, including an uninvested dorsal aorta and imperforate propterygium, and corroborate the early divergence of Cheirolepis within actinopterygian phylogeny. These traits represent conspicuous differences between the endoskeletal structure of Cheirolepis and Mimipiscis. Additionally, we describe new aspects of the parasphenoid, vomer and scales, most notably that the scales display peg‐and‐socket articulation and a distinct neck. Collectively, these new data help clarify primitive conditions within ray‐finned fishes, which in turn have important implications for understanding features likely present in the last common ancestor of living osteichthyans

Hétérostracés ptéraspidomorphes (Vertebrata) du Silurien supérieur et du Dévonien de Severnaya Zemlya (Russie) : données préliminaires et leurs implications biogéographiques et biostratigraphiques

La Terre-du-Nord (Severnaya Zemlya, paléocontinent Kara-Taïmyr) est une zone charnière pour comprendre les relations paléogéographiques entre le Continent des Vieux Grès Rouges et la Sibérie au Paléozoïque moyen. Sa série sédimentaire d\u27âge silurien supérieur et dévonien renferme une riche faune d\u27hétérostracés autorisant des corrélations biostratigraphiques avec essentiellement le Spitsberg (paléocontinent Barentsia), mais aussi avec l\u27Arctique Canadien (sur le Continent des Vieux Grès Rouges) et le Taïmyr central-Sibérie du NW (paléocontinent Siberia). Cette faune est composée d\u27assemblages variés depuis le Ludlow (Silurien supérieur) jusqu\u27au Frasnien (Dévonien supérieur) ; les assemblages les plus riches proviennent du Lochkovien supérieur et on observe un hiatus à l\u27Emsien (Dévonien inférieur).Severnaya Zemlya (Kara-Tajmyr palaeocontinent) is a key-zone in understanding the palaeogeographical relationships of the Old Red Sandstone Continent and Siberia in Mid-Palaeozoic times. Its Upper Silurian-Devonian sedimentary sequence bears a rich fauna of heterostracans which allows biostratigraphical correlation to be made with Spitsbergen (on the Barentsian palaeocontinent), but also with the Canadian Arctic (on the Old Red Sandstone Continent) and Central Tajmyr-NW Siberia (Siberian palaeocontinent). This fauna is composed of various assemblages from the Ludlow (Upper Silurian) to the Frasnian (Upper Devonian), with the richest assemblages in the upper Lochkovian, and a gap in the Emsian (Lower Devonian).</p

A new Lower Devonian arthrodire (Placodermi) from the NW Siberian Platform

A new genus and species of arthrodires, Eukaia elongata (Actinolepidoidei, Placodermi), is described from the Lower Devonian, ?Pragian of the Turukhansk region, NW&#160;Siberian Platform. A single specimen of the fish, a skull roof, comes probably from the lower part of the Razvedochnyj Formation. The occurrence of an actinolepidoid arthrodire in the Early Devonian of this area of Siberia is unexpected. Eukaia shows some distant relationship with the genus Actinolepis, but several features indicate similarity to representatives of other arthrodires

Devonian stratigraphy in Estonia: current state and problems

An updated version of the Devonian stratigraphical chart of Estonia with comments is presented. Estonian regional stratigraphical units are correlated with the standard conodont zonation and miospore zonation, used in the western part of the East European Platform. The fossil fish zonations, largely accepted in the Main Devonian Field, are discussed. Differences in the position of series and stage boundaries and age determination of regional units in the Baltic area, Belarus and NW Russia are dealt with. Two key markers for the correlation of the Middle Devonian of the Baltic area and Scotland, based mainly on placoderms, are described. Special attention is paid to occurrences of inarticulate brachiopods and finds of rare articulate brachiopods in siliciclastic rocks of the Baltic area, indicating their marine origin

A new Buchanosteid arthrodire (Placoderm fish) from the Early Devonian of the Ural Mountains

A new primitive brachythoracid arthrodire, Uralosteus bashkiricus gen. et sp. nov., is described from two Emsian (late Early Devonian) localities in the Ural Mountains of the Autonomous Republic of Bashkortostan, Russia. The holotype includes bones of the skull and trunk armor associated with numerous scales from one individual, which facilitates the study of isolated microremains. The dermal ornament of distinctive tuberculate ridges suggests a relationship to Errolosteus Young, 1981 from the Emsian of southeastern Australia, but neither form is well enough known for this to be strongly supported in a character analysis. Some isolated placoderm bones with ridged ornament from southeastern Australia are figured, and interpreted to belong to a new form of williamsaspid rather than to Errolosteus. The new genus Uralosteus is referred to the family Buchanosteidae, defined by a unique overlap arrangement of the posterior lateral onto the anterior dorsolateral plate of the trunk armor. Buchanosteids, as a basal brachythoracid group, are a key to understanding the phylogeny of that clade. The type genus Buchanosteus comes from southeastern Australia, but it is now evident that the family was widely distributed in shallow marine environments during the Emsian

Revision of Psammosteus livonicus Obruchev (Agnatha, Heterostraci) from the Devonian Amata Regional Stage of the NW of the East European Platform

The Devonian psammosteid agnathan Psammosteus livonicus Obruchev is revised using analysis of fossil material from collections in Russia, Latvia, Lithuania and Estonia that allowed the diagnosis and description of this species to be substantially extended. Psammosteus livonicus is similar to other species of Psammosteus in the characters of the dorsal plate, cyclomorial tesserae and stenobasal shape of the branchial plates. The study of the morphology of the branchial plates and tesserae (genus-level features) with consideration of species-level features of the ornamentation proves that the establishment of the genus Oredezhosteus Moloshnikov is baseless. The species Psammolepis aerata Obruchev in Halstead Tarlo 1965 and Oredezhosteus kuleshovi Moloshnikov 2009 are included as junior synonyms into the revised species based on the ornamentation features

Taxonomic revision of buchanosteoid placoderms (Arthrodira) from the early devonian of south-eastern australia and arctic Russia

The 'buchanosteid' placoderms are best known from the Early Devonian of Australia, but also occur in China, Russia, Central Asia and the Middle East. Here we rediagnose the type species Buchanosteus confertituberculatus (Hills 1936) from the type locality at Buchan, Victoria, in the light of new material of both head and trunk shields. The superfamily Buchanosteoidea Denison, 1978 is redefined to unite taxa that share a similar skull roof with separate rostro-pineal (ethmoid) bone, and postethmoid skull pattern characterised by a large trapezoidal nuchal, strap-like short and broad preorbitals, large subrectangular centrals, small postorbitals not contacting the paranuchals, and large, elongate marginal plates. The Family Buchanosteidae is redefined on skull roof and parasphenoid shape and trunk armour features as a monotypic family within the Buchanosteoidea. A new family (Parabuchanosteidae nov.) includes taxa with the posterior lateral plate overlapping the anterior dorsolateral plate externally. Two new buchanosteids are described, Richardosteus barwickorum gen. et sp. nov., from Burrinjuck, south-eastern Australia, and Urvaspis lithuanica gen. et sp. nov., from Severnaya Zemlya, Russia