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New Wenlock-Pridoli [Silurian] acanthodian fishes from Lithuania

100%

Valiukevicius J.

Acta Palaeontologica Polonica

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2004

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tom 49

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nr 1

Five new monotypic acanthodian genera and five new species are described from the Silurian (Wenlock to Pridoli) of Lithuania. Two new genera and species, Vesperalia perplexa and Fecundosquama basiglobosa, belong to climatiiform and three, Arenaceacanthus arcuatacanalis, Bracteatacanthus assiduus, and Rohonilepis breviornatus, to ischnacanthiform acanthodians. Vesperalia perplexa has high−crowned scales with ridges that cross the entire surface or frequently fade mid−crown and after a smooth area continue on the posterior edge. Stranggewebe in the crowns of V. perplexa scales has large oriented lacunae and a well−developed system of main vascular canals. Fecundosquama basiglobosa scales have an undeveloped neck, a crown with only marginal sculptural incisions and have an unusually large deep base. Simple bone−like mesodentine in the crowns of F. basiglobosa scales lacks principal vascular canals. Arenaceacanthus arcuatacanalis has diagnostic scales with anterior ridges that fade out at one−third of crown length, and crowns composed of simple acellular mesoand durodentine with the original arcuate radial vascular canals over the base. Bracteatacanthus assiduus scale crowns have short ridges of asymmetric profile and an antero−median sulcus, whereas scales of Rohonilepis breviornatus have sharp symmetric subradial crown ridges sloping towards the base. Scale crowns of B. assiduus and R. breviornatus are composed of dentine and durodentine, but the former is distinguished by a second area of multibranched radial vascular canals positioned high in the neck.

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Diversity of tissues in acanthodians with Nostolepis-type histological structure

63%

Valiukevicius J., Burrow C. J.

Acta Palaeontologica Polonica

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2005

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tom 50

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nr 3

Acanthodian scales with Nostolepis−type histological structure are separated into five groups based on the presence/absence and extent of stranggewebe, odontocytic and syncitial mesodentine networks, cellular unipolar mesodentine, bone−like mesodentine and durodentine in scale crowns. Two new families of acanthodians are erected, based primarily on histological structure of scales: the Vesperaliidae (stranggewebe extending throughout the scale crown) and the Acritolepidae (bone−like mesodentine in the scale crown). The latter family includes species erected for articulated fish. The families Tchunacanthidae and Lenacanthidae are united in the single family Tchunacanthidae, characterized by having scale crowns with mesodentine formed mainly by unipolar cells. A sixth group, which we exclude from the Nostolepis−type, has scale crowns composed of dentine without lacunae, plus durodentine, and bases with only rare osteocyte cavities. The new groups promote the revision and reassignment of many “nostolepid” taxa, in particular removing many species from the genus Nostolepis. Four new genera are erected: Pechoralepis (including part of Nostolepis), assigned to Acritolepidae nov.; and three genera assigned to an indeterminate family, which scales are composed of only odontocytic mesodentine without stranggewebe: Nostovicina (including part of Nostolepis), Nobilesquama (including part of Nostolepis), and Peregrinosquama (including part of Watsonacanthus). Histological structures are considered the primary characters of taxonomical value when based on isolated scales. Unfortunately, scale histology is unknown for most articulated acanthodians.

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Early Frasnian acanthodians from Central Iran

51%

Hairapetian V., Valiukevicius J., Burrow C. J.

Acta Palaeontologica Polonica

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2006

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tom 51

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nr 3

Two vertebrate−bearing horizons in the basal Frasnian carbonate of the Chahriseh section, northeast of Esfahan, yielded microremains of thelodonts, placoderms, acanthodians, actinopterygians, chondrichthyans, and sarcopterygians, considerably expanding the vertebrate faunal list for the strata. Acanthodians comprise a diverse association of climatiids, diplacanthids, and ischnacanthiforms, including the previously recorded climatiid Nostolepis sp. cf. N. gaujensis, as well as one new climatiid genus and several taxa left in open nomenclature. Climatiid Iranolepis ginteri gen. et sp. nov. is diagnosed by having scales with a highly raised medial crown area separated by steep slopes from lateral crown areas; an odontocytic mesodentine of maximum extent in the crown, distinguished by extensive network of fine canaliculi with abundant tiny osteocytes; and a poorly developed stranggewebe system. Other scales with fan−like symmetrically grooved crowns conform to the Diplacanthus−type histologically, and have many characters in common with Milesacanthus antarctica from the Aztec Siltstone of Antarctica. Osseous gnathal elements include mesodentinous tooth whorls from an ischnacanthiform or climatiid, and ischnacanthiform jaw bones with large chambers for vascular canals, distinctly separated cylindrical tooth cusps along the lingual ridge, and wide−based, triangular, weakly striated cusps on the main lateral ridge. The acanthodian association, accompanied by the Frasnian conodonts of the middle Mesotaxis falsiovalis to Palmatolepis hassi zones and zonal thelodonts Turinia hutkensis and Australolepis seddoni, is proving useful for biostratigraphy, showing similarities with assemblages from both Gondwana and the Old Red Sandstone Continent.

Ograniczanie wyników

3 Acta Palaeontologica Polonica

3 Valiukevicius J.

2 Burrow C. J.

1 Hairapetian V.

1 2006

1 2005

1 2004

New Wenlock-Pridoli [Silurian] acanthodian fishes from Lithuania

Diversity of tissues in acanthodians with Nostolepis-type histological structure

Early Frasnian acanthodians from Central Iran