PREDATORS AND PREYS AMONG MARINE TRIASSIC FISHES

The various fish faunas that followed one another throughout the Triassic were dominated, right from the start, by phylogenetically primitive top-predators such as Saurichthys and Birgeria, later on joined by some paleonisciforms still during the Early Triassic and by the subholostean Gabanellia in the Norian. Coelacanths were also widespread throughout the Triassic: their size could well exceed 150 cm, especially during the Middle Triassic, when also Birgeria increased in length, up to nearly 300 cm. Judging from the teeth, anyway, fish of all sizes were involved in active predation, mainly of other fishes: from very small taxa (less than 5 cm in length) like Prohalecites and some Peltopleurus, to the small to medium sized Sangiorgioichthys, or the ‘flying’ fish Thoracopterus. Saurichthys is by far the most common among large predators, several species being well above 100cm. In some cases, helped by the scarce scale-covering of its body (often consisting of only few longitudinal scale rows), it exceptionally shows the gut content preserved. Generally it contains very small preys, swallowed whole. Only one find of a Ladinian Saurichthys species is an exception: the evidence suggests it used to eat floating dead specimens, behaving as a scavenger. Among the rare testimonies concerning predation, some other involve the same genus Saurichthys in the role of prey: large specimens are found smashed in Middle Triassic units. The investigation of coprolites very seldom reveals fish remains, while shell fragments are common in the Norian coprolites because large durophagous fishes, such as Paralepidotus and Sargodon, living and preying on the sea bottom, were widely spread. Actually, predation on shelled organisms was already performed by actinopterygians as early as in Early Triassic: the suction-feeder Bobasatrania crushed mollusk shells by means of pharyngeal tooth-plates. During the Middle Triassic too, several taxa were provided with blunt teeth. Though, the single teeth were still quite small and brought by surfaces which appear unfit for processing very hard shells. That strictly durophagous fishes are quite rare in Early and Middle Triassic is also supported by the uncommon presence of hybodont sharks.