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.

The Mongolepidida is an Order of putative early chondrichthyan fish, originally erected to unite taxa from the Lower Silurian of Mongolia. The present study reassesses mongolepid systematics through the examination of the developmental, histological and morphological characteristics of scale-based specimens from the Upper Ordovician Harding Sandstone (Colorado, USA) and the Upper Llandovery–Lower Wenlock Yimugantawu (Tarim Basin, China), Xiushan (Guizhou Province, China) and Chargat (north-western Mongolia) Formations. The inclusion of the Mongolepidida within the Class Chondrichthyes is supported on the basis of a suite of scale attributes (areal odontode deposition, linear odontocomplex structure and lack of enamel, cancellous bone and hard-tissue resorption) shared with traditionally recognized chondrichthyans (euchondrichthyans, e.g., ctenacanthiforms). The mongolepid dermal skeleton exhibits a rare type of atubular dentine (lamellin) that is regarded as one of the diagnostic features of the Order within crown gnathostomes. The previously erected Mongolepididae and Shiqianolepidae families are revised, differentiated by scale-base histology and expanded to include the genera Rongolepisand Xinjiangichthys, respectively. A newly described mongolepid species (Solinalepis levis gen. et sp. nov.) from the Ordovician of North America is treated as family incertae sedis, as it possesses a type of basal bone tissue (acellular and vascular) that has yet to be documented in other mongolepids. This study extends the stratigraphic and palaeogeographic range of Mongolepidida and adds further evidence for an early diversification of the Chondrichthyes in the Ordovician Period, 50 million years prior to the first recorded appearance of euchondrichthyan teeth in the Lower Devonian.

The exoskeleton, consisting of micromeric elements (odontodes) and their derivatives, is characteristic of the most ancient vertebrates. Great morphological and histological variability of discrete exoskeletal microremains makes it difficult to identify them. It is necessary to study not only separate scales or tesserae, but also to get a picture of the squamation in general, because species determined from discrete elements are understood as an assemblage of morphological types. For determination of discrete exoskeletal elements, their morphology, internal structure, defined tissue types of crown and basal plate, types (way) of their growth, system of vascular canals should be studied in addition changes occuring during ontogenetic development of both the dermal skeletal elements and the squamation should be taken in consideration. The material of different groups of early vertebrates (astraspids, tesakoviaspids, heterostracans, thelodonts, mongolepids, chondrichthyans and acanthodians), which were widely distributed in the Early Palaeozoic, are used as examples.

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Abundant microvertebrate remains from the Siberian Platform are described as early acanthodians. All are preserved with both excellent morphology and histology. They are assigned to a new order, Tchunacanthida, with two new families, Lenacanthidae and Tchunacanthidae. These comprise two new genera, Lenacanthus and Tchunacanthus with type species L. priscus sp. nov. and T. obruchevisp.nov. The evidence from the morphology and histology is that they are the most ancient acanthodian scales so far found. The total collection of vertebrate material from the Irkutsk amphitheatre is described, together with their geological distribution, geographical range and systematic palaeontology. Head scales, tesserae of three morphotypes, transitional scales and body scales have been found. All comprise morphological sets as determined by comparison of morphology using SEM and of histology using Nomarsky interference optics. Observations of growth were possible from details of concentric lines on the crown and also from incremental layers seen in both horizontal and vertical sections. Starting from the primordial scale, consecutive layers are added, coronally, laterally, and deep in the corium onto the base; these occurred simultaneously in both crown and base. A type of areal-superpositional growth occurred in some body scales but in other scales there was little superpositional growth. It is concluded that Tchunacanthus possessed very solid body armour with tightly joined scales covering a large area of the body, and scale bases deeply set in the corium. Both tissues of the scales, dentine and bone, feature enclosed cells. This character is regarded as primitive within acanthodians, as in derived forms both tissues are acellular. Acanthodian scales are one of many examples of transformation from cellular to acellular tissue in evolution.

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Abstract. The biostratigraphic and palaeogeographical distributions of early vertebrate microfossils from a number of Lower Silurian localities in northwestern Mongolia, Tuva and southern Siberia were reviewed. Vertebrate microremains showed high taxonomic diversity, comprising acanthodians, chondrichthyans, putative galeaspids, heterostracans, mongolepids, tesakoviaspids, thelodonts and possible eriptychiids. The majority of taxa have lower stratigraphic levels of occurrence compared to other Silurian palaeobiogeographical provinces, such as the European-Russian or Canadian Arctic. Vertebrate microremains are numerous within the samples, which may indicate warm-water low-latitude palaeobasins with rich shelf faunas. This disagrees with the recent interpretations of the territory as a northern high-latitude Siberian palaeocontinent. The palaeobiogeographical distribution of vertebrate taxa indicates an endemic palaeobiogeographical province of connected epeiric palaeoseas with external isolation during the early Silurian. In previous works separation between Tuvan and Siberian palaeobiogeographical provinces has been suggested. After careful revision of the vertebrate microfossil record of the region, we find that differences in a few vertebrate taxa do not provide not strong enough evidence to reliably distinguish these provinces. We therefore dispute the hypothesis of two biogeographical provinces in the early Silurian of the Siberian palaeocontinent, and propose a single unified Siberian–Tuvan palaeobiogeographical province.

Luk ß evics, E., Lebedev, O. A., Mark-Kurik, E. and Karataj u te-Talimaa, V. 2009. The earliest evidence of host-parasite interactions in vertebrates. -Acta Zoologica (Stockholm) 90 (Suppl. 1): 335-343Traces of parasite action have been discovered in the Middle-Upper Devonian fish from Estonia, Latvia and European Russia. Such traces are known in heterostracan Psammolepis venyukovi , antiarchs Asterolepis radiata and Bothriolepis ciecere , sarcopterygians Holoptychius sp., Ventalepis ketleriensis and Eusthenodon sp. nov. The traces include evidence of parasitic fixation and penetration as well as dwelling traces. Pathologies are developed as (1) round fossulae on the external surface of bones and scales; (2) oval fossulae with a slight elevation in the centre of the pit; (3) hollow swellings (possible galls); (4) openings (perforations) that have been repaired to various degrees; (5) variously shaped buttresses on the visceral surface of sarcopterygian scales; and (6) porous spongy formations on the non-overlapped surface of sarcopterygian scales. The round fossulae in sarcopterygian, placoderm and psammosteid skeletal elements could be produced by parasites that are similar to copepod crustaceans. Gall formation in Asterolepis is most likely to be caused by a larva, possibly of a trematode. The perforations of scales (and dermal bones) might arise from the attacks of ectoparasites (copepods?) or different worms. The spongy formations on the Holoptychius scales could be the result of invasion of a unicellular parasite.Erv i ns Luk ß