Chitinozoan biostratigraphy in the Ordovician of BaltoscandiaNõlvak, Jaak2002 http://www.ester.ee/record=b1035650*est Comparative morphological analysis of the early Paleozoic marine impact structures Kärdla and Neugrund, EstoniaSuuroja, Sten2007 https://digi.lib.ttu.ee/i/?141 https://www.ester.ee/record=b2305374*est