The Middle Devonian fishes of the Baltic States (Estonia, Latvia) and Belarus

An overview of the range of the Middle Devonian fishes from the Baltic states, Estonia and Latvia, and Belarus is given. The Baltic outcrops, in particular, have yielded a rich and diverse fish fauna containing agnathans (heterostracans, osteostracans), chondrichtyans, placoderms, acanthodians, crossopterygians, dipnoans, and actinopterygians. The representatives of some groups (osteostracans, chondrichthyans, palaeoniscoids) which possess an exoskeleton consisting of small elements, are comparatively poorly known and need description. However, acanthodians present an exception here: the scales of these fishes have been thoroughly studied by Valiukevicius. The acanthodians are out of the scope of this paper, except some species of special interest. Several fish groups, psammosteid heterostracans, placoderms, crossopterygians, and probably dipnoans were represented during the Arukula and Burtnieki Ages by very large forms. The fish fauna became somewhat less diverse beginning with the Gauja Age and later. Placoderms and some other fishes are close to those known in the Middle Devonian of Scotland, being favourable to the correlation of the sections in these regions. The data on the Middle Devonian fishes in Belarus are less abundant. Still, they show some differences with the Baltic faunas of the same age. The Eifelian of Belarus has yielded phlyctaeniid arthrodires, in the late Eifelian (Gorodok Regional Stage) occur various chondrichthyans; both in the Eifelian and Givetian the occurrences of ptyctodonts and palaeoniscoids are common.