Review of the Ordovician conodont zonal index Eoplacognathus suecicus Bergström, 1971

Over 600 elements of the Ordovician conodont index Eoplacognathus suecicus Bergström, 1971, were obtained from the Segerstad and Skärlöv Limestones at the Lunne section, which is the type locality of E. suecicus, and at the Kullstaberg section both in Jämtland, Sweden. Specimens of E. suecicus from different stratigraphic levels and representing different growth stages show obvious morphological differences. The stratigraphically early elements of E. suecicus are very similar to the stratigraphically late elements of Eoplacognathus pseudoplanus (Viira), being distinguished mainly by the appearance of the secondary postero-lateral denticle row in the stelliplanate element. Eoplacognathus suecicus apparently was derived from E. pseudoplanus, and probably evolved into Eoplacognathus lindstroemi (Hamar).