Discovery of trimerellide brachiopod Gasconsia from the Ordovician of Estonia

In this study, the first trimerellide brachiopods from Estonia are described. They occur in the uppermost Katian (Upper Ordovician) shallow shelf environments and represent some of the largest Ordovician brachiopods. The trimerellides described are assigned to the genus Gasconsia Northrop, 1939, which disappears before the Hirnantian and reappears in the lowermost Wenlock after a long interregnum. In the Baltic Basin, the new data from Estonia expand the distribution area of Gasconsia from the Scandinavian facies belt in the west to the Estonian shallow shelf in the east. Despite poor preservation, the specimens studied revealed some structures in shell morphology important for species level identification. The strati­graphic position of Gasconsia is analyzed relative to the Katian-Hirnantian (Pirgu-Porkuni regional stages) boundary and the occurrence of the late Katian brachiopod Holorhynchus in Estonia. The improved data on the distribution of Gasconsia in time and space and a short discussion on brachiopod gigantism are presented.