CARNIAN/NORIAN CONODONTS FROM THE PIZZO MONDELLO SECTION (MONTI SICANI, WESTERN SICILY), GSSP CANDIDATE FOR THE BASE OF THE NORIAN: INTEGRATED BIOSTRATIGRAPHY, PHYLOGENY AND STABLE ISOTOPE ANALYSES.

Pizzo Mondello section (Sicani Mountains, Western Sicily, Italy), is one of the best localities for the definition of the Carnian/Norian boundary (CNB). The section is a 430 m thick continuous succession of marine limestones, characterized by uniform facies, ranging from Late Carnian to Rhaetian (Upper Triassic), named Calcari con selce. The section is entirely exposed and it shows high sedimentation rates of 20-30 m/m.y. (Muttoni et al., 2004). Pizzo Mondello section is not affected by diagenetic overprint and it thus preserves the original paleomagnetic and geochemical record and, moreover, it yields several biostratigraphically significant fossil groups. The conodont and radiolarian records are in fact very rich and, furthermore, the Calcari con Selce of the Western Sicily, and especially of the Sicani Mountains, are well known all over the world for the exceptionally rich and well preserved Late Carnian to Early Norian ammonoid faunas studied by G.G. Gemmellaro (1904) and for the very rich halobiid record (Gemmellaro, 1882; Montanari & Renda, 1976; Cafiero & De Capoa Bonardi, 1982; De Capoa Bonardi, 1984; Levera, 2009: PhD Thesis in progress). At present conodonts are considered the most useful tool to define the CNB.
Thus, in order to find the most suitable conodont bioevent as primary biomarker for the CNB and to solve some problematic issues concerning the biostratigraphy and phylogeny of some Upper Triassic conodonts, the first 143 m of the section, where the CBN interval is located, were sampled in detail to conduct integrated taxonomic, biostratigraphic, phylogenetic and ecological studies on the conodont populations.
The five most widespread Upper Triassic conodont genera (Paragondolella, Carnepigondolella, Metapolygnathus, Epigondolella and Norigondolella) have been revised in detail: this revision allowed to make very accurate biostratigraphic correlations of Pizzo Mondello with the other most complete Upper Triassic sections in the world, and to recognize some discriminating morphological features for the separation of these five genera and many others for the classification of the species. The changes in the conodont platform morphology observed through the section provided the following trends in the evolution of the pectiniform elements: a) the forward-shifting of the pit; b) the shortening of the platform; c) the gradual posterior prolongation of the keel end and d) the appearance of nodes on the platform margins and the evolution of nodes into denticles. Species belonging to the five studied genera have been thus assigned to two separate monophyletic lineages: i) the Paragondolella-Metapolygnathus lineage and ii) the Carnepigondolella-Epigondolella lineage.
Nevertheless, the phylogenetic relationships of some species remained still problematic. In order
to solve these problems, numerical cladistic analyses have been applied to the studied species. The morphological characters used to classify conodont species have been thus codified to generate numerical matrices and then analyzed by PAUP software (Swofford, 2002) under the parsimony criteria. The cladograms evidenced morphological relationships among genera and species, showing that the evolutionary trends identified are supported by the most parsimonious character states distribution among taxa, confirming the importance of the considered characters for the conodont systematic and revealing also other new important diagnostic characters. The cladistic analyses clarified thus the phylogenetic relations between the studied taxa: Paragondolella resulted the most probable forerunner genus of all the other Upper Carnian/Norian genera and Norigondolella is strictly related to it; Metapolygnathus and Epigondolella are recognized as two monophyletic groups while