Fish biodiversity in the marine Norian (Late Triassic) of northern Italy: The first Neopterygian radiation

Abstract The Middle‐Late Norian (220–215 Mya) vertebrate fauna from the Zorzino Limestone had numerous neopterygian genera. Though known since the Permian, neopterygians were not particularly diverse until the Norian, when major orders (Semionotiformes, Pycnodontiformes, Macrosemiiformes, Pholidophoriformes) radiated. Currently, 12 genera belonging to these orders are known from this fauna, a few more awaiting description. Palaeopterygians are also well represented (e.g., Sauricbthys, Birgeria, Thoracoptenis and Gabanellid). Genera showing durophagous dentitions, adapted for crushing or nibbling different prey, belong to the Neopterygii, while paleopterygians mainly have predatory adaptations. Thus it is likely that the radiating neopterygians were not able to compete with more primitive forms on the highest trophic levels of active predation. Compared to earlier actinopterygians they developed an ‘underexploited’ trophic adaptation, durophagy. A new, more favourable environment was unlikely to have been ...