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 regional British Llandeilian Stage of the Llanvirn Series was first described in a classical study by Rhodes more than 65 years ago using single element (form) taxonomy. Although several subsequent authors have recorded a substantial number of conodont taxa from the Llandeilo area, the present study is the first to present a modern taxonomic review of these late Darriwilian-early Sandbian faunas that include approximately 20 multielement species. Most prominent are representatives of Amorphognathus, Baltoniodus, Eoplacognathus, and Plectodina. The study faunas have their own biogeographical character. The distinctive genera Complexodus, Protopanderodus, and Pygodus, which are common in coeval Baltoscandic faunas, are not present, but the occurrence of Amorphognathus, Baltoniodus, and Eoplacognathus provides a link to age equivalent Baltoscandic faunas. The presence of abundant specimens of Plectodina and less common representatives of Erismodus and Icriodella are reminiscent of North American Midcontinent faunas. This type of faunal assemblage is in some respects similar to those of the early Caradoc Series of the Welsh Borderland. 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.