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.The fossil record of Devonian tetrapods, the earliest and most primitive limb-bearing members of the tetrapod stem group, was for many decades restricted to the iconic 'four-legged fish' Ichthyostega from the Famennian (latest Devonian) of Greenland 1-5 and the fragmentary genus Acanthostega from the same strata 2 . During the last 20 years, intense collecting and research has produced complete skeletal material of Acanthostega 6-8 and a series of new taxa, greatly expanding the temporal and geographical range of these animals. Devonian tetrapods are now known from as early as the late Frasnian, the earlier part of the Late Devonian period, and have been recorded from Gondwana and north China as well as Laurussia 9-18 . However, most of these new forms remain very poorly known, typically represented by no more than lower jaw rami or isolated postcranial bones; Acanthostega and Ichthyostega are still the only Devonian tetrapods known from near-complete skeletons. We know less about the fishtetrapod transition than the taxic diversity suggests.Among the more fragmentary forms are five (Metaxygnathus, Densignathus, Elginerpeton, Obruchevichthys and Ventastega) that combine a characteristically tetrapod lower-jaw morphology with the retention of coronoid fangs and other 'fish' characters absent in Acanthostega, Ichthyostega and more crownward limbed members of the tetrapod stem group 19,20 . These genera seem to fall into the morphological gap between Acanthostega and Ichthyostega and the (paraphyletic) elpistostegids, but all except Ventastega are very incomplete. Ventastega was originally described in 1994 from the Pavāri locality in the late Famennian Ketleri Formation of Kurzeme, western Latvia 21 (Supplementary Information 1). Further excavations at this site up to 2001 have yielded an extensive body of material, including previously unknown or incompletely known elements such as a near-complete skull roof plus braincase and associated cheek (Fig. 1), scapulocoracoid, anocleithrum, interclavicle and ilium (Fig. 2). All come from a single horizon, and the occurrence of multiple identical examples of several elements (jaws, cheek plates, maxillae, clavicles, cleithra, nasals) indicates that only ...
Ventastega curonica, from the Upper Famennian Ketleri Formation, is the first tetrapod find from the Upper Devonian of Latvia, and only the fourth adequately represented Devonian tetrapod genus to be described. The taxon is represented by disarticulated cranial and postcranial elements from two localities, Ketleri on the Venta River and Pavari on the Ciecere River. A second tetrapod, represented by a single mandibular fragment, appears to be present at Ketleri. The lower jaw of Ventastega is strikingly primitive in retaining fangs on the coronoid series, but shares many characters with those of other known Devonian tetrapods. Some of these features are interpreted as basal tetrapod synapomorphies; they provide a new data set for the identification of isolated tetrapod jaw fragments, and confirm the (previously disputed) tetrapod status of Metaxygnathus. The upper jaw bones of Ventastega are broadly similar to those of Acanthostega, Ichthyostega and Tulerpeton, as is the narial region. The lateral rostral bone is either very small or absent. A preopercular bone is present in the cheek, and the lacrimal is excluded from the orbit. The palate is closed. Palatine and vomer bear fangs which are set in the marginal tooth row. An isolated iliac blade from Pavari, probably attributable to Ventastega, resembles that of Acanthostega but may not have carried a dorsal process. Two clavicles from Pavari and Ketleri which may also belong to Ventastega are of a typical early tetrapod pattern, similar to Greerpeton but with a broader ventral blade. Non-attributable or doubtfully attributable bones from Ketleri include a probable tetrapod postorbital and a possible limb bone. Ventastega appears to be a tetrapod of the same broad `grade' as Ichthyostega and Acanthostega, but is arguably more primitive than either.
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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