Michele Mazza

A new Metapolygnathus platform conodont species and its implications for Upper Carnian global correlations

A rich conodont fauna from two Neotethyan sections, Pizzo Mondello (western Sicily, Italy) and Pignola 2 sections (southern Apennines, Italy) includes conodonts described herein as a new species. Metapolygnathus praecommunisti sp. nov. is transitional between Paragondolella noah and Metapolygnathus communisti. The genus Metapolygnathus (including M. praecommunisti) is now characterised by posterior prolongation of the keel termination, associated with a centrally located pit and with a weak ornamentation confined to the anterior part of the platform margins. The establishment of M. praecommunisti addresses the problems related to the origin and the peculiar, probably facies-controlled, distribution of its descendant species M. communisti. Since M. praecommunisti occurs in the entire Tethys and in North America, we propose the species as a good guide fossil for global correlations, characterised by a short temporal range limited to the uppermost Tuvalian (upper Carnian). The stratigraphic occurrence of the genus Metapolygnathus is restricted to the Tuvalian—Lacian (upper Carnian—lower Norian), excluding its presence in the Julian substage (lower Carnian).

Application of numerical cladistic analyses to the Carnian–Norian conodonts: a new approach for phylogenetic interpretations

The high intraspecific variability of conodont platform elements in the upper Carnian–lower Norian interval and the proliferation of numerous species in this relatively short time have generated many problems for the understanding of Late Triassic conodont phylogeny, systematics and taxonomy. Since Late Triassic natural assemblages are still unknown, we have applied cladistic methodologies to investigate the evolution of Carnian–Norian conodont platforms and to infer more precise phylogenetic relationships among taxa. Numerical cladistic analysis was undertaken of species belonging to the five Late Triassic genera Paragondolella, Carnepigondolella, Metapolygnathus, Epigondolella and Norigondolella. A taxon–character data matrix describing the distribution of 64 characters amongst two outgroups and 31 ingroup taxa was compiled and processed using PAUP* 4.1. Our analyses show the evolutionary and systematic value of certain morphological characters, and lead to a reinterpretation of the phylogenetic position of the genera considered: Metapolygnathus, Epigondolella and Norigondolella are monphyletic taxa, Paragondolella represents a polyphyletic assemblage of basal members of the ingroup, and Carnepigondolella a paraphyletic group including primitive forms of the Metapolygnathus and Epigondolella lineages. Our analyses also clarify the systematic position of ‘Metapolygnathus communisti B’ and confirm the existence of four new species: Carnepigondolella angulata sp. nov., Epigondolella heinzi sp. nov., Epigondolella miettoi sp. nov. and Norigondolella trinacriae sp. nov.

New insights into the diversity dynamics of Triassic conodonts

In this paper, we examine the diversity trends and the evolutionary patterns of Triassic conodonts through a newly powered large-scale data-set compiled directly from the primary literature. Paleodiversity dynamics analyses have been undertaken by working at the species level and using a system of time units based on biozone subdivisions for a fine temporal level resolution. The role of heterogeneous duration of taxa in diversity estimates has been evaluated through the probabilistic profiles. Results reveal three different stages in the diversity behaviour of Triassic conodonts from standing metrics delimited by two inflections at the mid-Anisian and mid-Carnian. Survivorship analysis supports this pattern. Origination–extinction metrics report a diversification pattern characterised by important fluctuations during the Lopingian–Induan (earliest Triassic), the early-middle Olenekian (Early Triassic) and the Anisian–Ladinian transitions (Middle Triassic), as well as in the early Late Triassic. In addition, two clear diversification peaks are observed in the late Carnian and in the end-Norian. Reported patterns are interpreted in the context of deep extinction and environmental instability by documenting the biological signal of the main diversification and turnover patterns observed from such records. This study emphasises the singularity behaviour of diversity trends derived from the conodont record.

New Upper Triassic Conodont Biozonation of the Tethyan Realm

Conodonts are biostratigraphically very important microfossils in the Upper Triassic, occurring in different marine habitats, from deep-ocean to shallow-shelf waters. Because of their great abundance, worldwide distribution, strong resistance to rock metamorphism, and mineralogical composition that makes them reliable tools for biostratigraphic and geochemical studies, conodonts have proven to be important tools in defining the Geological Time Scale (GTS) and Global Stratotype Section and Points (GSSPs). We present here an original Upper Triassic conodont biozonation for the Tethyan Realm integrated, where possible, with ammonoid and radiolarian zones, providing also numerical ages for stages and substages. Based on the most recent conodont biostratigraphic and systematic studies, we propose a subdivision of the Upper Triassic interval into 22 conodont zones (nine for the Carnian, ten for the Norian, and three for the Rhaetian), correlated, where possible, with the most recent North American conodont zonations. Discussions on the most biostratigraphically important conodont taxa are also provided, in particular for the stratigraphic intervals around the base of the Norian and Rhaetian stages, the GSSPs of which have yet to be defined. In this view, we provide data supporting the validity of conodonts as reliable tools for global correlations, recommending two conodont biovents as possible primary biomarkers: the FAD (First Appearance Datum) of Metapolygnathus parvus for the base of the Norian and the FAD of Misikella posthernsteini for the base of the Rhaetian. The conodont species Norigondolella carlae n. sp. from the upper Tuvalian (Carnian) is also defined.