NEW DATA ON LATE ORDOVICIAN ECHINODERMS FROM SARDINIA, ITALY

Late Ordovician echinoderm faunas from Sardinia, Italy remain poorly documented and previous investigations have yielded largely fragmentary material belonging to blastozoans and crinoids. Although several blastozoan taxa had previously been named, few were based on articulated thecae, and feeding appendages were unknown. New collections from the Upper Ordovician (Katian) Portixeddu Formation at various localities near Portixeddu and Fluminimaggiore, southwestern Sardinia, Italy contain numerous complete specimens including previously unknown taxa. The fauna has a rich diversity of taxa including brachiopods, bryozoans, gastropods, bivalves and echinoderms. Echinoderms were common at localities near Portixeddu and include hemicosmitoids, coronoids and diploporitans but relatively few crinoids and glyptocystitoids. Echinoderms collected near Fluminimaggiore include numerous crinoids (including cladids and camerates), hemicosmitoids and coronoids, but relatively few diploporitans and glyptocystitoids. Based on associated brachiopods, the difference in relative abundances of these taxa likely reflects differences in water depth. In both areas, echinoderms were associated with root-like holdfasts suggesting that at least some of the taxa were autochthonous. Several specimens are preserved with intact oral areas and feeding appendages, which are significant for clarifying the phylogenetic position of these taxa.

Taphonomic, sedimentologic, and palaeontologic data suggest that the fauna colonized the upper offshore soft substrates from the Mediterranean margin of Gondwana during the first pulses of the mid-late Katian global warming Boda Event. The Sardinian echinoderm fauna shows a stronger affinity to coeval Iberian communities than Moroccan communities. Specimens are preserved as natural moulds in siltstones and some specimens are slightly strained by weak tectonic overprinting. Fossils accumulated in obrution deposits resulting from storm events favoring the preservation of delicate structures.