New Hirnantian orthide brachiopods from the type section of the Porkuni Stage (Porkuni quarry, northeastern Estonia)

Four new Hirnantian species of orthide brachiopods, Sigmelasma peepi, Mendacella aerinensis, Drabovia? minuta and Tyronella siugensis are described from the type section of the Porkuni Regional Stage in the Porkuni quarry, northeastern Estonia. These species occur in the reef-related shallow-water bituminous limestone (Siuge Member of the Ärina Formation). Sigmelasma peepi and Tyronella siugensis represent the families Wangyuiidae and Tyronellidae, respectively, which were hitherto unknown in the Baltic Ordovician. Additionally, a harknessellid Reuschella sp. is described from the stromatoporoid-coral reefs (Tõrevere Member) and skeletal grainstone (Vohilaid Member) of the same locality and formation. Together these new finds extend our knowledge of the latest Ordovician brachiopod fauna in the Baltic region, showing higher than previously expected diversity of the Porkuni Stage and distinctness of reef-related brachiopods in the shallow shelf environment. The new species are not present in the Hirnantia brachiopod fauna in deeper-water environments of the Central East Baltic.