First report of hybodont shark from the Toarcian Rosso ammonitico formation of Umbria-Marche Apennine (Polino area, Terni, central Italy)

In this contribution we present the first material referable to hybodont shark from the Rosso Ammonitico Formation (Umbria-Marche-Sabina Palaeogeographic Domain). Two teeth were recovered isolated within Toarcian red marly-limestone (Bifrons Zone). The best-preserved tooth is characterized by a general structure well in accord with the classic crushing dentition typical of hybodont sharks within the Subfamily Acrodontinae. The gently domed occlusal surface of the tooth does not show any trace of occlusal crest and of wrinkles, and is characterized by densely pitted, finely reticulated ornamentation. The available characters allow a conservative classification of the material at the genus level as Asteracanthus sp. The best-preserved tooth can be referred to the most mesial area of the first row of lateral teeth, using as a reference the holotype of Asteracanthus medius. The new material represents the earliest evidence of Asteracanthus and the second one from the whole Northern Apennines (Central Italy), throwing new light on the dispersal of the genus on the Jurassic Tethys.