New genus of chondrichthyans from the Silurian – Devonian boundary deposits of Tuva (Russia)

Abstract

A new genus of Chondrichthyes from the uppermost Silurian–lowermost Devonian deposits of central Tuva (Russia) is described on the basis of the microremains (scales). A sample from the Khondergei Formation of the Bazhyn-Alaak locality in the Tchadan region contained scales of a new chondrichthyan, Tuvalepis schultzei gen. et sp. nov., together with another chondrichthyan, Elegestolepis grossi KARATAJŪTĖ-TALIMAA, 1973, as well as numerous scales of the thelodont Helenolepis navicularis KARATAJŪTĖ-TALIMAA, 1978. The scales of T. schultzei display significant morphological variation and are characterized by a very fine, comparatively wide and flat crown with longitudinal ribs and a small and short neck. The growth pattern of T. schultzei scales is very different from that of elegestolepids described so far – the scales grew by appositional addition of layers towards the distal side of the crown, in contrast to the scales of Elegestolepis grossi which lack any kind of concentric growth lines.