Original paper

Problematic scale-like fossils from the Ordovician of Siberia with possible affinities to vertebrates

Dzik, Jerzy; Moskalenko, Tamara A.


Microtomography and sectioning of the morphologically variable scales of Kodinskaspis angarensis gen. et sp. nov. from the Mamyry Formation of the Irkutsk Basin of Siberia (early Mid Ordovician, 460 Ma) show that their formation started from minute conical thin-walled units (cusps). The whole body of the cusp, as well as the structurally identical phosphatic lamellar tissue common for the whole scale, was secreted basally. V-shaped series of cusps accreted to the anterior margin of the scale during its growth. The mineral tissue of the Siberian scales resembles atubular dentine of some Late Ordovician to Early Silurian (450-440 Ma) fish scales from the same region of the world, associated with regular dentine or bone. A tissue similar in structure, secretion mode and location is known also in conodonts, referred to as the basal body tissue. Its homology with dentine finds some support from this new evidence. It is suggested that the new finding represents the geologically oldest and morphologically simplest member of the Siberian tesakoviaspidids.