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One of the identifying characteristics of tetrapods (limbed vertebrates) is the presence of fingers and toes. Whereas the proximal part of the tetrapod limb skeleton can easily be homologized with the paired fin skeletons of sarcopterygian (lobe-finned) fish, there has been much debate about the origin of digits. Early hypotheses 1 interpreted digits as derivatives of fin radials, but during the 1990s the idea gained acceptance that digits are evolutionary novelties without direct equivalents in fish fin skeletons. This was partly based on developmental genetic data 2 , but also substantially on the pectoral fin skeleton of the elpistostegid (transitional fish/ tetrapod) Panderichthys, which appeared to lack distal digit-like radials 3 . Here we present a CT scan study of an undisturbed pectoral fin of Panderichthys demonstrating that the plate-like 'ulnare' of previous reconstructions is an artefact and that distal radials are in fact present. This distal portion is more tetrapod-like than that found in Tiktaalik 4 and, in combination with new data about fin development in basal actinopterygians 5 , sharks 6 and lungfish 7 , makes a strong case for fingers not being a novelty of tetrapods but derived from pre-existing distal radials present in all sarcopterygian fish.A near-complete specimen of Panderichthys from the late Middle Devonian period (385 million years ago; see Supplementary Information) of Lode, Latvia (Institute of Geology at Tallinn University of Technology specimen number GIT434-1) forms the basis of this study. Although the dorsal part of the skull and left side of the body have suffered substantial damage from a mechanical excavator, the specimen was originally well preserved. Notably, its body axis is straight (determined from the alignment of dorsal midline scales and the symmetry plane of the skull) and it appears less dorsoventrally compressed than others from the same locality. This is shown, for example, by the narrow skull outline and near-vertical cheek-plate fragments, distinctly different from the flattened and splayed skulls that have been published 8,9 . The specimen also contains the only known pelvis and pelvic fin skeleton of Panderichthys 10 .The right pectoral fin and most of the shoulder girdle are preserved in articulation, with the fin concealed under the body. This region of the specimen was CT scanned at the East-Tallinn Central Hospital (see Methods Summary and Supplementary Methods). The scanned region comprises the entire fin endoskeleton and an estimated 40% of the lepidotrichial fin web, as well as most of the shoulder girdle. The presence of X-ray-reflective crystal growths in the shoulder region unfortunately prevented complete modelling of the scapulocoracoid. The entire fin is covered by scales and lepidotrichia, which cannot be modelled individually but are easily separated from the darker endoskeleton. The leading or preaxial margin of the fin is dipping ventrolaterally into the substrate (Fig. 1a-c). In contrast to early tetrapods, in which the limb projects at...

Lebedev, O.A., Mark-Kurik, E., Karataj u t E -Talimaa, V.N., Luk ß evi ç s, E. and Ivanov, A. 2009. Bite marks as evidence of predation in early vertebrates. -Acta Zoologica (Stockholm), 90 (Suppl. 1): 344-356Study of lifetime bite traces on agnathans and fish (or gnathostomes) from Ukraine, Estonia, Latvia and north-western and central European Russia reveals evidence of predator-prey relationships in communities of Devonian age. Numerous bite traces on skeletal parts of agnathan pteraspidiforms and psammosteiforms, placoderm arthrodires and antiarchs and sarcopterygian porolepiforms and osteolepiforms are described. Evidence of healing shows that prey organisms responded to predation by reconstruction of damaged skeletal elements. Ichthyofaunistic analysis is used to establish possible predators. The most probable predators in the Middle and Late Devonian communities are sarcopterygian porolepiforms and osteolepiforms. Predatory tetrapods become evident during the Famennian. Global analysis of aquatic predators during the Silurian-Devonian interval shows a gradual increase in species numbers with time. During the Late Silurian, only ischnacantid acanthodians, early osteichthyans and sarcopterygians are known to belong to this trophic group. By the end of the Devonian this list is complemented by chondrichthyans, arthrodires, porolepiform, osteolepiform, struniiform and rhizodontiform sarcopterygians and tetrapods. Only Devonian agnathans show no predatory groups. In sarcopterygians, predatory dentitions, which developed according to more or less the same pattern, show little change during the Devonian.

ABSTRACT. The tetrapodomorph sarcopterygian Livoniana multidentata gen. et sp. nov. is described on the basis of lower jaw fragments from the Middle Devonian (late Givetian) of Latvia and Estonia. It possesses a suite of derived characters previously only known from tetrapods, which ®rst appear in the late Devonian (late Frasnian), and a phylogenetic analysis places it on the internode between Panderichthys and the base of the Tetrapoda. The analysis also reveals that the`Elpistostegalia' are paraphyletic to Tetrapoda, with Elpistostege closer to tetrapods than is Panderichthys. Owing to incompleteness of the material, there is almost no overlap between the data sets for Elpistostege and Livoniana; the analysis places the two genera in an unresolved trichotomy. In addition to the tetrapod features, Livoniana has a strikingly autapomorphic dentary dentition comprising multiple tooth rows. It thus provides evidence both for the unexpectedly early evolution of tetrapod characteristics and for morphological radiation around the ®sh-tetrapod transition. D U R I N G the last two decades, a series of new discoveries has greatly increased our knowledge of Devonian tetrapods.

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The Kačák Event is a late Eifelian (Mid-Devonian) episode of marine dysoxia/anoxia with associated extinctions. It has been widely recognized in the shelf seas that surrounded the Old Red Sandstone continent. It was contemporary with the lacustrine Orcadian Basin in Scotland. This basin contains the distinctive Achanarras lake horizon that contains a rich and diverse fish fauna. The Achanarras lake was wide and deep and would have been filled by rainfall from a monsoon system at an insolation maximum. Faunal elements within the lake are in common with the Kernavė Member in Estonia and this level can be conodont dated as late Eifelian eiflius or ensensis Zone. Therefore the group of lacustrine flooding climatic events that occur at and above the Achanarras level can be correlated with the marine Kačák Event (sensu lato) and both can be regarded as having a common climatic cause and driven by an insolation maximum. A reconstruction of the Orcadian Basin drainage system and a water balance model based on the calcium flux within the lake shows that a very significant volume of water would have been seasonally discharged to the Rheic Ocean and would have caused an additional environmental effect.

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