Biostratigraphy and taxonomy of three-dimensionally preserved nemagraptids from the Middle and Upper Ordovician of Baltoscandia

Biostratigraphically significant finds of two important species of Nemagraptus in the Middle and Upper Ordovician carbonate sections of Baltoscandia are reviewed. Nemagraptus subtilis is found in the lower part of the Uhaku Regional Stage, which is correlated with the Hustedograptus teretiusculus graptolite zone. Nemagraptus gracilis is restricted to the upper part of the Kukruse Stage in the Central and South Estonian and western Latvian sections. This level correlates with the Nemagraptus gracilis graptolite Zone. the vertical distribution of these taxa is similar to, although less complete than, their ranges in the classic black shale succession in Scania, southern Sweden. the first three-dimensionally preserved specimens of N. subtilis are illustrated and described. Nemagraptus subtilis can be differentiated from N. gracilis by its lack of cladial branches, more slender stipes, shorter sicula, and upward orientation of the first two thecae.