Radula und Fangarme beiMichelinoceras sp. aus dem Silur von Bolivien

New finds of michelinoceratid cephalopods from the Kirusillas-Shale (Ludlow/Silurian) of Ushpa-Ushpa in the Eastern Cordillera of the Bolivian Andes reveal parts of the radula and imprints of arms owing to extremely good preservation conditions. The imprints of soft parts point that the orthoce-rates had 10 arms, two of them shaped to long tentacles as recent coleoids have. Of more importance is the first proof of a michelinoceratid radula in situ. This is the first known ra-dula of lower palaeozoic cephalopods at all. TheMichelinoceras radula consisted of 7 teeth per row. So the radulae of michelinoceratid cephalopods are very similar to those of ammonites and coleoids. But there are great differences in the radula ofMichelinoceras sp. and that ofNautilus sp. All known radulae of fossil and recent cephalopods are compared and phylogenetic or systematic implications are discussed. The classification of the cephalopods into six subclasses as used in the “Treatise” turns out to be unnatural and should be given up. Finally ecological relations between the morphology of radula-elements and mode of life are dis-cussed. Size and number of radula teeth let suppose that thisMichelinoceras specimen must have been an adult individual living far off the coast in pelagic seas.