Hybodont sharks from Jurassic PCP-Basin systems of Umbria Marche Apennines

The Umbria-Marche-Sabina (hereafter UMS) Domain in Central and Northern Apennines hosts a Upper Triassic to Neogene sedimentary succession recording a rifting stage occurred by the late Hettangian, dismembering a Bahamian-type carbonate platform. Tectonic subsidence and palaeoceanographic/palaeoecological perturbations diachronically led to the drowning of the benthic factory, triggering the onset of different styles of sedimentation in PCP-basin systems up to the deposition of the Maiolica Fm. since the Tithonian p.p. The new topographic configuration enabled burgeoning trophic niches available both for the vertebrate and invertebrate fauna. While the invertebrate fossil record of the UMS Domain is wealthy, vertebrate remains are relatively less represented and, thus, to date under-investigated. Three specimens consisting of teeth attributed to hybodont sharks are here discussed. Two specimens are isolated teeth referred to as Asteracanthus sp. coming from early Toarcian (Bifrons Zone) red marly-limestone of the Rosso Ammonitico Fm. (Polino, Umbria, Italy). The third specimen comes from the “Bugarone superiore Fm.” of the Monte Nerone PCP (Piobbico, Marche, Italy). It consists of five teeth in anatomical connection and some fragments referred to as Asteracanthus cf. A. magnus. In the Mesozoic, hybodont sharks dominated a wide range of ecological niches, displaying many different dentition patterns and lifestyles. On the whole, the teeth here reported fit well a dentition pattern known as “Type broyeur”, typical of extreme crushing feeding behaviour, characterizing Jurassic hybodont sharks feeding on the seafloor. The genus Asteracanthus has a cosmopolitan distribution in the Jurassic of Tethys and has been reported from several palaeoenvironments; in the present case, the taxon is related to open marine settings. By considering the invertebrate fauna that inhabited PCP-basin contexts of UMS Domain, potential prey living on the sea-floor are ostreids, limids, terebratulid brachiopods, gastropods and crustaceans. Zooxanthellate corals from several PCP-top and basin-margin condensed successions indirectly extend the in-depth Asteracanthus outreach to more than 100 m, increasing the range depth previously reported for this taxon. View publication