The ammonite assemblages found in the spathic Fu3 shell beds (lumachellas) of the Grilli Quarry (Furlo Pass, Umbria-Marche Apennines, central Italy) supplement the previous studies on the early Pliensbachian (Carixian) in this area, allowing to obtain a quite varied taxonomic, biostratigraphic and paleobiogeographic framework. The abundant documentation of the three lumachellas forming the Fu3 fauna (Fu3a, Fu3b1 and Fu3b2) belongs to the second Apennine biozone of the early Pliensbachian: this unit was formerly indicated as Miltoceras sellae Taxon Range Biozone, but here is redefined in a formally more correct way as Miltoceras Interval Biozone. Among the several ammonites collected, many new taxa are described: the new species Miltoceras furlense (family Coeloceratidae, subfamily Coeloceratinae), the new genus Spiniclaviceras for the new species S. spirale (family Coeloceratidae, subfamily Dubariceratinae), the new genus Paramorphites with the new species P. acutiventris (family Polymorphitidae, subfamily Polymorphitinae), and the new genus Sphenoacanthites (family Sinuiceratidae) instituted for the Tunisian forms erroneously reported as Gorgheiceras costotuberculatum and G. tuberculatum. Moreover, the new Polymorphitidae subfamily Furlitinae is formalized, also to include (with some doubt) Gemmellaroceras. This latter genus has been often subject of taxonomic confusion, and therefore a precise definition is given for it, allowing to clarify its bioand chronostratigraphic position. Since in the Apennines Gemmellaroceras is found only from the second early Pliensbachian biozone onwards, this genus cannot be considered as a representative of the basal part of the stage at issue. The diagnosis of Miltoceras is improved too, basing on an unpublished revision of the original material housed in the “G.G. Gemmellaro” Geological Museum of the Palermo University. In addition, three unnamed new forms are recognized: one ascribed to the Dubariceratinae, one to the nominal subfamily of the Tropidoceratidae, and one which position at a suprageneric level cannot be determined. Basing on the whole of the available data, phylogenetic and paleobiogeographic hypotheses for some Mediterranean Tethys ammonoids are discussed, and a quite wide taxonomic synthesis is proposed. The Apennine documentation allows considerations on the Sinuiceratidae and the earliest Tropidoceratidae, but seems also to testify the first evolutive phases of the Polymorphitidae. This latter group is deemed to be the possible ancestor of the Fanninoceratidae (genera Eoamaltheus and Fanninoceras) of the eastern Pacific area (Andean Province). From a paleobiogeographic point of view, the features of the Apennine lower Pliensbachian ammonite faunas suggest that a limited portion of the western Tethys can be considered as a “Peltolytoceratinae meso-Mediterranean paleobiogeographic unit”. This shallow and mid-depth marine region would have included Apennines, Tuscany, Sicily, Albania, North Africa (Morocco, Algeria, northern Tunisia) and perhaps also Betic Cordillera (Spain) and Austrian Alps. Its relations with other areas are discussed, as well as the possibility of westward faunal exchanges (although sometimes partial and discontinuous) with the Andean Province. Indeed, the available evidence suggests that the trans-Pangea seaway known as the “Hispanic Corridor” would have acted as a filter, allowing the migration only to some forms which probably lived in relatively shallow environments (e.g. Catriceras and Paramorphites), but not to those for which a more deep habitat can be inferred (e.g. Galaticeras).

Download Article