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Abstract

Conodonts have played an important role in the construction of a Triassic timescale. Each of the stage boundaries is reviewed in the context of their evolving conodont faunas. The base Triassic (Induan) is defined by the appearance of Hindeodus parvus, which developed from H. praeparvus; a parallel zonation is provided by Neogondolella species. For the Induan–Olenekian boundary, the appearance of Neospathodus waageni sensu lato within a plexus of similar species is favoured as the defining datum; Borinella and Eurygnathodus also appear about this time. The base of the Middle Triassic Anisian stage lies close to the appearance of Chiosella, with Triassospathodus and Spathicuspus characterizing the late Olenekian, and Gladigondolella tethydis and Nicoraella confined to the Anisian. Proxies for the Anisian–Ladinian boundary, which is defined by an ammonoid, are the first Budurovignathus species. The basal Carnian, also defined by an ammonoid, lies close to the first metapolygnathids, including M. polygnathiformis and M. tadpole. The Carnian–Norian boundary interval is characterized by many new taxa in Canada, but only a few species are common to Tethys, notably Metapolygnathus ex gr. M. echinatus. The Norian–Rhaetian boundary is likely to be based on evolution in Misikella in Tethys, with concurrent changes recognized in North American Epigondolella.

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