Acritolepis Valiukevičius, 2003a

Valiukevičius, Juozas & Burrow, Carole J., 2005, Diversity of tissues in acanthodians with Nostolepis-type histological structure, Acta Palaeontologica Polonica 50 (3), pp. 635-649 : 644

Genus Acritolepis Valiukevičius, 2003a

Type species: Acritolepis ushakovi Valiukevičius, 2003a ; Severnaya Zemlya Archipelago , Matusevich River , outcrop 1, bed 21; Lower Devonian , Lochkovian, Severnaya Zemlya Formation .

Species included: Type species and A. urvantsevi Valiukevičius, 2003a .

Diagnosis.—Small−sized moderately deep−bodied acritolepid acanthodian with low−angled dorsal spines bearing six longitudinal ribs per side, long thick−walled pectoral spines with eight ribs per side, two pairs of prepectoral spines and slender cylindrical scapula. Spines composed of a thick layer of lamellar vascularized bone surrounding the large central cavity, overlain by osteodentine and odontocytic mesodentine. Dentigerous jawbones have large principal tooth cusps of a triangular shape with smaller secondary cusps between forming the lateral main tooth row, and striated blunt denticles on the lingual edge; tiny palatine teeth are also present. Flank scales grew superpositionally; they are relatively small (<0.5 mm wide), with two to six parallel flattened uniform anterior ridges extending one−third of crown length; short neck and deep base; bone−like highly odontocytic mesodentine is composing most of the crown, with only a small area of stranggewebe in the posteriormost part of flank scale crowns. Largely varying in shape, tectal plates and tesserae of the head region are tuberculated, ridged, striated or stellate, of areal growth, polyodontode histologically, composed of lamellar acellular bone basally, cellular vascularized bone with osteon structures in the mid−layer, and odontocytic mesodentine superficially.