Peregrinosquama, 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 : 647

Genus Peregrinosquama nov.

Derivation of the name: From peregrinus (Latin) other, strange and squama (Latin) scale.

Type and species: Peregrinosquama costata ( Valiukevičius, 2003a) ; Severnaya Zemlya Archipelago , Spokojnaya River , outcrop 48, bed 5; Lower Devonian , lower Emsian, lower Al’banov Subformation .

Age and geographic distribution: Lower Devonian, lower Emsian. Severnaya Zemlya Archipelago, Timan−Pechora region, Salair, Taimyr ( Russia).

Species included: Peregrinosquama oervigi (Sobolev, Karatajūtė− Talimaa, and Valiukevičius, 1988) and Peregrinosquama costatus ( Valiukevičius, 2003a) .

Diagnosis.—Scale crowns have three to six sharp radial ridges pointing posteriorly or rarely fading out at crown midlength; neck is low, and the base is massive, protruding strongly in front of the crown; scale crowns composed of dentine with long, narrow ascending vascular/dentinal canals, of which the main branches are in the posterior part, with a syncitial mesodentine (intermediate between dentine and mesodentine) in the anterior crown part and a more orthodentine−like tissue posteriorly; crown tissues without lacunae and stranggewebe, with outer parts of growth lamellae composed of a highly refractive durodentine; finely laminar bone in scale base contains small numbers of randomly distributed osteocyte cavities.

Discussion.—Morphologically, the scales most closely resemble those of Watsonacanthus Valiukevičius, 1979 , but histologically, scales of the latter belong to the third group of the Nostolepis − type structure. The ornament on scale crown resembles that of Nostolepis , Laliacanthus , Eifellepis , Acritolepis , and other genera, but they also differ histologically. By histological characters, Peregrinosquama gen. nov. is in an intermediate position between the Nostolepis and Acanthodes − types, and differs from Nobilesquama gen. nov. by its massive, anteriorly−protruding base, in having durodentine in all crown growth zones, and relatively narrow ascending vascular canals.