Nostovicina, Valiukevičius & Burrow, 2005

Valiukevičius, Juozas & Burrow, Carole J., 2005, Diversity of tissues in acanthodians with Nostolepis-type histological structure, Acta Palaeontologica Polonica 50 (3), pp. 635-649 : 646

Genus Nostovicina nov.

Comment.—The new genus Nostovicina is erected for the former Nostolepis spp. of the third group, in which scale crowns have only an odontocytic mesodentine lacking stranggewebe.

Derivation of the name: From the first syllables of Nostolepis , and Latin vicinalis, neighboring, close, referring to the similarity with Nostolepis .

Type species: Nostovicina fragila ( Valiukevičius, 2003a) ; Severnaya Zemlya Archipelago , Matusevich River , outcrop 1, bed 21; Lower Devonian , Lochkovian, Severnaya Zemlya Formation .

Age and geographic distribution: From the Upper Silurian, Pridoli, through to the Lower Devonian, Emsian. Severnaya Zemlya Archipelago, Timan−Pechora region, Taimyr ( Russia), Arctic Canada, North Greenland, Baltic, China, Australia, New Zealand.

Species included: Nostovicina applicata ( Vieth, 1980) , N. athleta ( Valiukevičius, 1994) , N. curiosa ( Valiukevičius, 1994) , N. curta ( Valiukevičius, 1994) , N. fragila ( Valiukevičius, 2003a) , N. guangxiensis ( Wang, 1992) , N. halli ( Blom, 1999) , N. lacrima ( Valiukevičius, 1994) , N. laticristata ( Valiukevičius, 1994) , N. multangula ( Valiukevičius, 1994) , N. multicostata ( Vieth, 1980) , N. paravolborthi ( Valiukevičius, 2003b) , N. platycrista ( Valiukevičius, 2003b) , N. spina ( Valiukevičius, 1994) , N. tareyensis ( Valiukevičius, 1994) , and N. timanica ( Valiukevičius, 2003a) .

Diagnosis.—Acanthodians which have short longitudinally ribbed pectoral spines and two pairs of wide, stout, shallowly inserted ventral (prepelvic) spines with diagonal nodose ribs which converge with the quadrangular leading rib; highsculptured tesserae stellatae of areal growth on the head area and small trunk scales usually showing superpositional growth; scale crowns may be flat and smooth ( Minioracanthus Valiukevičius, 1985 ; Paranostolepis Vieth, 1980 ) to moderately−inclined ( Canadalepis Vieth, 1980 ) bearing subparallel or rarely subradial anterior ridges which fade out posteriorly, and sometimes form a slightly raised medial area; fin spines composed of highly vascularized cellular bone and odontocytic mesodentine; crowns of tesserae and scales composed of a moderately cellular odontocytic mesodentine network mainly lacking enlarged vascular canals; some species with thin layers of durodentine developed in outer laminae; no stranggewebe in scale crowns.

Discussion.—The combination of characters which diagnose Nostovicina gen. nov. are variously represented in other taxa, making its affinities uncertain. The genus resembles some representatives of the Climatiidae , which are known from articulated specimens, in spine shape, but differs by the number of ventral (prepelvic) spines, e.g., Euthacanthus Powrie, 1864 has six pairs, Brachyacanthus Egerton, 1861 and Lupopsyrus Bernacsek and Dineley, 1977 have four pairs, and Ptomacanthus Miles, 1973 has three pairs. Fin spine structure resembles that of the Acritolepidae . The morphology of scales and fin spines of N. fragila resemble those of Lupopsyrus pygmaeus Bernacsek and Dineley, 1977 , from the Lower Devonian of Canada, but the scales of Lupopsyrus are monodontode ( Hanke and Wilson 2004).