Middle-Upper Ordovician conodonts from the Ffairfach and Golden Grove groups in South Wales, United Kingdom

The conodont fauna of the reference succession of the British regional Llandeilian Stage of the Llanvirn Series was fi rst described in a now classical study by Rhodes (1953) using single element (form) taxonomy. Although some subsequent authors have recorded a few additional conodont taxa from this late Darriwilian- Sandbian interval at Llandeilo and coeval strata in nearby areas (e.g. Bergström, 1964, 1971; Bergström and Orchard, 1985), the present study is the fi rst to present a complete taxonomic review of these faunas, which include approximately 20 multielement species. Most prominent among the compound conodont taxa in these fauna from South Wales are representatives of Amorphognathus, Baltoniodus, Eoplacognathus, Icriodella, and Plectodina. Biostratigraphically diagnostic species indicate that the Llandeilo study succession ranges from the Eoplacognathus lindstroemi Subzone of the Pygodus serra Zone to the Baltoniodus variabilis Subzone of the Amorphognathus tvaerensis Zone. The Llandeilo faunas have their own biogeographic character. The common occurrence of species of Plectodina and less common representatives of Erismodus and Icriodella are reminiscent of coeval North American Midcontinent faunas but the latter lack Baltoniodus and Eoplacognathus. The Llandeilo conodont species association is also somewhat similar to that of the Caradoc Series of Welsh Borderland (Bergström, 1971; Savage and Bassett, 1985) but the latter differs in lacking, among others, Baltoniodus, and Eoplacognathus. These two genera are common in coeval Baltoscandic faunas, but the latter also contain such characteristic genera as Complexodus, Protopanderodus, and Pygodus, which are not represented in our Llandeilo collections. Because specimens of Plectodina are quite rare, and Erismodus is missing, in the coeval Baltoscandic faunas, the faunal similarity between the Baltoscandic and the South Wales faunas is quite limited.