A NEW UPPER ORDOVICIAN (KATIAN) CRINOID FAUNA FROM SARDINIA, ITALY

The Ordovician was a pivotal time in the evolutionary history of stemmed echinoderms in terms of the origination of major Paleozoic clades, significant climatic shifts, and the Great Ordovician Biodiversification Event. Our understanding of these events is based largely on assemblages from Laurentia, while lacking a representative sampling from other paleocontinents, most notability Gondwana. To help correct this bias, a new crinoid fauna is described from Perigondwanan Sardinia, Italy. Disarticulated ossicles including abundant crinoid columnals have been previously reported from the Late Ordovician Portixeddu Formation in southeastern Sardinia.

A new collection of the Portixeddu fauna has yielded a diverse assemblage of pelmatozoan echinoderms including abundant hemicosmitoids and coronoids along with rare diploporitans, glyptocystitoids, echinosphaeritids, and crinoids. The crinoids are restricted to small obrution deposits and delicately preserved as external molds. Despite their limited spatial distribution, this assemblage has a diversity that is amongst the highest reported from the Katian of Gondwana. Recovered taxa include three new diplobathrid camerates, a dendrocrinid cladid, and two disparids. The majority of these taxa are represented by only one or two specimens, which suggests a much higher diversity than was recovered. Of particular note, amongst this fauna are new crinoid genera from the Anthracocrinidae and Maennilicrinida, which are the first reported occurrence of these clades within Gondwana. A description of the Portixeddu fauna provides new insight into the paleogeography and evolutionary history of Late Ordovician crinoids.