Late Ordovician conodont faunas from southern Sardinia, Italy: biostratigraphic and paleogeographic implications

Conodont faunas recovered from several localities in southwestern and southeastern Sardinia are assigned to the Late Ordovician on the basis of the recovery of Amorphognathus ordovicicus Branson and Mehl, 1933 and A. lindstroemi (Serpagli, 1967). A peculiar Amorphognathus species that has been found in slightly older sediments is described. 28 species belonging to 18 genera constitute the conodont collection; elements of Hamarodus europaeus (Serpagli, 1967) and Scabbardella altipes (Henningsmoen, 1948), together with those of Amorphognathus, numerically dominate the fauna. The same dominance was already reported in the 'Tonflaserkalk' of the Carnic Alps (Serpagli, 1967). Taxa of the genera Plectodina, Dichodella, Sagittodontina, Istorinus and Icriodina are described and discussed for the first time for Sardinia. The conodont fauna, composed at about 13000 elements obtained by the processing of about 550 kg of limestones, includes species typical of the Mediterranean Province. Nevertheless, the extreme paucity of its markers Sagittodontina robusta Knupfer, 1967 and Istorinus erectus Knupfer, 1967, which together represent less than one per cent, of the fauna, and the presence of other typical indicators of lower latitude affinity like Plectodina and Dichodella reveal the mixed character of Sardinian fauna. Together with the Carnic Alps, Sardinia probably occupied an outer position of lower latitudes (compared to the typical north-Gondwanian regions of the circumpolar belt) where faunistic interchange with both the British and Baltic provinces was possible.