Event pattern in the development of Siluro-Devonian acanthodians of Lithuania

In the Silurian of Lithuania, three most significant acanthodian originations are distinguished: in the Ventspils Formation and the Suderve Beds (Neris Formation) of the mid-Pagegiai Regional Stage, which supposedly followed the mid-Ludfordian extinction of many faunal lineages in the Baltic; in the uppermost Minija Formation in the west and its correlatives the Vievis and Pabrade formations in east Lithuania (early Pridoli); and at the Minija/Jura or Vievis/Lapes boundary (early/late? Pridoli) of the western and eastern parts respectively. The latter two are of particular importance for acanthodian radiation in the Pridoli. The genus Nostolepis is most abundant within the transitional taxa. A remarkable turnover of the acanthodian fauna is confined to the Silurian/Devonian boundary mirroring a regression in sea level and isolation of the Silurian Basin producing endemic acanthodians. Devonian associations differ in having more distinctly characterized, abrupt changes in taxonomic composition, with a prevalence of transitional taxa at a few levels only. The early Lochkovian is still Nostolepis-dominated due to many taxa continuing through the Silurian boundary, whereas the late Lochkovian is marked by new genera. Most pronounced faunal originations and diversifications are attached to the Rezekne (Emsian or Eifelian?) and the upper Ledai - Kernave formations in the uppermost Eifelian. Four intervals of significant acanthodian turnover occur in the Lochkovian upper Tilze Formation, the Pragian-early Emsian (many extinctions), the Eifelian lower Ledai Formation, and at the Givetian/Frasnian boundary.