Taxonomy, evolution and biostratigraphy of the Ordovician conodont genera Triangulodus and Tropodus

Triangulodus and Tropodus are re-defined based on revision of three species from Australia and reassessment of all other previously assigned species. Although sharing some similarities in apparatus structure, these genera originated in the middle–late Tremadocian (Early Ordovician) as two separate clades, corresponding to a major evolutionary event affecting conodonts. Species of Tropodus lack a symmetrical tricostate Sa element and display basally bifurcated costae in one or more element types, with a quinquecostate Sd element and typically a multi-costate Sc element. Triangulodus emanuelensis is revised based on the primary types and abundant topotypes from the Emanuel Formation (Lower Ordovician) of the Canning Basin in Western Australia and numerous specimens from other coeval stratigraphic units in the Canning (e.g., Nambeet Formation) and Amadeus (e.g., Horn Valley Siltstone) basins and from the Tabita Formation in far western New South Wales. Tropodus repetskii sp. nov. is described, defining the Tropodus repetskii-Paroistodus proteus Biozone in the lower part (upper Tremadocian) of the Emanuel Formation. This new species is closely related to Tropodus bifidus from the Lower Ordovician Hunghuayuan Formation in South China. The new taxonomic and phylogenetic data of these two genera and their constituent species documented in this contribution enhance their value to biostratigraphy. Yong Yi Zhen [[e-mail]], Geological Survey of New South Wales, W.B. Clarke Geoscience Center, 947–953 Londonderry Road, Londonderry NSW 2753, Australia