THE TRIASSIC ACTINOPTERYGIAN FISH REVOLUTION

The real impact of the big P/T crisis on the actinoptegyian fish faunas has not been yet understood. Though, the recovery is known to have been fairly rapid: two or three million years after the crisis an impressive radiation led to a greatly diversified Anisian fauna, with a wide range of trophic and swimming specializations. We have also to consider that a few highly specialized taxa were already present in latest Permian, for example the top-predator Saurichthys and the durophagous suction-feeder Bobasatrania. Soon after the P/T crisis, they were joined by other top predators like Birgeria and by some pleonisciform survivors, all together making up the Triassic Early Fish Fauna (TEFF). Except for Bobasatrania, most of these fishes lived in open marine waters. As proved by the rich assemblages found in South China and in the Southern Alps, the start of the real, dramatic change took place in the Spathian and had its apex between the Pelsonian and the Illyrian (Middle-Late Anisian), giving rise to the Triassic Middle Fish Fauna (TMFF). The top-predators (Saurichthys and Birgeria) lived throughout the Triassic; in the meantime some necto-benthonic forms appeared, whose teeth are specially made for picking up and then processing organisms provided with an exoskeleton. Their specialization, however, is lower than that shown later on by the much larger crushing teeth of some of the taxa making the Triassic Late Fish Fauna (TLFF), appeared in the Norian. Associated to this kind of trophic specialization is often a deep body shape, which helps in maneuvering close to the bottom. These characteristics apply both to the basal neopterygian (Luoxiongichthys, Kyphosichthys) belonging to the South China assemblages (East Tethys) and to the subholosteans (Felberia, Stoppania, Ctenognathichthys) of the alpine sites (West Tethys). The same two groups share another novelty of the TMFF: the appearance of very small taxa, far less than 50 mm long. These ‘lilliput’ forms represent a new trophic level among the nectonic organisms. From the Norian, when also the reefal environments completed their recovery, the strictly durophagous taxa appeared with pycnodonts and the large semionotids (Paralepidotus), which were then widely spread throughout the rest of the Mesozoic.