Microstructure of paleoniscid fi sh scales from Irati Formation, Permian (Cisuralian) of Paraná Basin, Brazil

Abstract

The Permian paleoichthyofauna of Paraná Basin is poorly known, mainly due to lack of more complete specimens, especially in the levels from Irati Formation. Recently fossil specimens were collected on this unit, in a mine of pyrobetuminous shale on PETROBRAS-SIX Company, at São Mateus do Sul, Paraná State. The material is only composed by disarticulated scales and some parts of the fins. To histological studies the fish scales were included in resin, sectioned in thin sections and observed in petrographic microscope. The well-preserved histological material allows observing: an external layer, with the enamel type ganoine exhibiting an evident stratification and several pores, a middle layer, the dentine, with visible odontodes containing pulp cavity and dentinal tubules and an inner layer, the isopedine, with growth lines and spaces left by osteocytes and the blood vessels feeding the bone tissue. Sections were also displayed in the scale traces of growth tissue and show structures similar to that previously record in the group. The histology of the material and the structures of peg-and-socket type observed, allowed assigning this material to paleoniscids. The morphology and histological arrangement was also compared with other previous work made to the Paraná Basin and show a histological character similar to types P-1 and P-2 (Elonichthys punctatus?) firstly described.

Key words: histology, Actinopterygii, paleoniscid, ganoine, dentine, isopedine.