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The known diversity of tetrapods of the Devonian period has increased markedly in recent decades, but their fossil record consists mostly of tantalizing fragments 1-15 . The framework for interpreting the morphology and palaeobiology of Devonian tetrapods is dominated by the near complete fossils of Ichthyostega and Acanthostega; the less complete, but partly reconstructable, Ventastega and Tulerpeton have supporting roles 2,4,16-34 . All four of these genera date to the late Famennian age (about 365-359 million years ago)-they are 10 million years younger than the earliest known tetrapod fragments 5,10 , and nearly 30 million years younger than the oldest known tetrapod footprints 35 . Here we describe Parmastega aelidae gen. et sp. nov., a tetrapod from Russia dated to the earliest Famennian age (about 372 million years ago), represented by three-dimensional material that enables the reconstruction of the skull and shoulder girdle. The raised orbits, lateral line canals and weakly ossified postcranial skeleton of P. aelidae suggest a largely aquatic, surface-cruising animal. In Bayesian and parsimony-based phylogenetic analyses, the majority of trees place Parmastega as a sister group to all other tetrapods.

The species of the Late Devonian, earliest Famennian placoderm fish Bothriolepis jeremejevi has been downranked to subspecies Bothriolepis leptocheira jeremejevi comb. nov. in a result of detailed morphological studies of the type specimens and abundant new material from the type locality of the Sosnogorsk Formation, South Timan, Komi Republic, Russia. This taxon closely resembles Bothriolepis leptocheira leptocheira from Scotland, B. leptocheira curonica from Latvia, and B. leptocheira ssp. from Severnaya Zemlya differing only in small deviations of the size, proportions and shape of some plates of the armour. The composition of vertebrate assemblages from Scotland, Latvia, and Severnaya Zemlya containing B. leptocheira demonstrates a reduced diversity of antiarch placoderm, acanthodian, and sarcopterygian fishes; however, the Sosnogorsk assemblage differs in a larger diversity containing very primitive tetrapod and diversified sarcopterygian fishes including dipnoans and porolepiforms but lacking acanthodians. Wide distribution of a single species of Bothriolepis and usually diminished diversity of vertebrates suggest that the earliest Famennian vertebrate assemblages conform the survival faunas of the latest Frasnian-earliest Famennian biotic crisis. [ABSTRACT FROM AUTHOR]

Lukševičs, E., Ahlberg, P.E., Stinkulis, Ģ., Vasiļkova, J. & Zupiņš, I. 2011: Frasnian vertebrate taphonomy and sedimentology of macrofossil concentrations from the Langsēde Cliff, Latvia. Lethaia, Vol. 45, pp. 356-370. The siliciclastic sequence of the Upper Devonian of Kurzeme, Western Latvia, is renowned for abundant vertebrate fossils, including the stem tetrapods Obruchevichthys gracilis and Ventastega curonica. During the first detailed taphonomic study of the vertebrate assemblage from the Ogre Formation cropping out at the Langsēde Cliff, Imula River, abundant vertebrate remains have been examined and identified as belonging to one psammosteid, two acanthodian and three sarcopterygian genera; the placoderm Bothriolepis maxima dominates the assemblage. Besides fully disarticulated placoderm and psammosteid plates, separate sarcopterygian scales and teeth, and acanthodian spines, partly articulated specimens including complete distal segments of Bothriolepis pectoral fins, Bothriolepis head shields and sarcopterygian lower jaws have been found. The size distribution of the placoderm bones demonstrates that the individuals within the assemblage are of approximately uniform age. Distinct zones have been traced within the horizontal distribution of the bones. These linear zones are almost perpendicular to the dominant dip azimuth of the cross-beds and ripple-laminae and most probably correspond to the depressions between subaqueous dunes. Concavity ratio varies significantly within the excavation area. The degree of fragmentation of the bones and disarticulation of the skeletons suggest that the carcasses were reworked and slightly transported before burial. Sedimentological data suggest deposition in a shallow marine environment under the influence of rapid currents. The fossiliferous bed consists of a basal bone conglomerate covered by a cross-stratified sandstone with mud drapes, which is in turn overlain by ripple laminated sandstone, indicating the bones were buried by the gradual infilling of a tidal channel. All the Middle-Upper Devonian vertebrate bone-beds from Latvia are associated with sandy to clayey deposits and have been formed in a sea-coastal zone during rapid sedimentation episodes, but differ in fossil abundance and degree of preservation. □ Agnathans, Devonian, facies analysis, fish, fossil assemblage, palaeoenvironment. [ABSTRACT FROM AUTHOR]

The gap in our understanding of the evolutionary transition from fish to tetrapod is beginning to close thanks to the discovery of new intermediate forms such as Tiktaalik roseae. Here we narrow it further by presenting the skull, exceptionally preserved braincase, shoulder girdle and partial pelvis of Ventastega curonica from the Late Devonian of Latvia, a transitional intermediate form between the ‘elpistostegids’ Panderichthys and Tiktaalik and the Devonian tetrapods (limbed vertebrates) Acanthostega and Ichthyostega. Ventastega is the most primitive Devonian tetrapod represented by extensive remains, and casts light on a part of the phylogeny otherwise only represented by fragmentary taxa: it illuminates the origin of principal tetrapod structures and the extent of morphological diversity among the transitional forms. [ABSTRACT FROM AUTHOR]