The assemblages of Middle Devonian psammosteid agnathans from the eastern part of Main Devonian Field

The stratigraphical and geographical distributions of psammosteid taxa were detailed for the Middle and lower Upper Devonian of the Main Devonian Field (MDF). The composition of psammosteid assemblages from the western and eastern parts of MDF was compared. This analysis shows the differences in the stratigraphical ranges or the miss of some psammosteid taxa in those parts. Thus, Schizosteus asatkini Obruchev and Schizosteus ? sp. occurs in the eastern part of MDF, but Tartuosteus ? luhai Mark-Kurik is common for Latvia and Estonia and was not found in the eastern part. The Abava psammosteid assemblage could not be defined in all MD F. The psammosteids of the Amata Regional Stage in the eastern part differ in the presence of Psammolepis venyukovi Obruchev, Psammosteus cf. cuneatus Obruchev, Psammosteus sp. 3. On account of Psammolepis undulata (Agassiz), a zonal species by L.B. Halstead Tarlo, was recorded older than the Amata interval, a new Psammosteus praecursor psammosteid Zone is proposed here for the Amata Regional Stage.