Silurian graptolite biozones of Lithuania: present and perspectives

Graptolites are a group of extinct colonial invertebrate organisms, which belong to hemichordates. They are the most important organism group of Silurian biostratigraphy in Lithuania. A lot of new material appeared recently that made possible the potential for the improvement of the graptolite biozonation of Lithuanian Silurian. In Lithuania graptolites are distributed from Coronograptus cyphus (upper Ruddanian) to Neocolonograptus lochkovensis (lower Pridolian). The intervals of Rhuddanian–Aeronian, Telychian–Sheinwoodian, Gorstian–Ludfordian and Ludlow–Pridoly boundaries are still problematic in Lithuania and further studies are necessary.