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Implicazioni della presenza di Ptychodus decurrens Agassiz 1839 (Elasmobranchi, †Ptychodontidae) nel cretaceo Sup del Passo del Furlo, Italia Centrale


Abstract


It
L'autore riporta la presenza ed il significato paleo-ecologico di denti dello squalo ibodonte estinto Ptychodus decurrens Agassiz 1839 nelle radiolariti bituminose cenomaniane (Cretacico Superiore) del Passo del Furlo, Pesaro. Questa segnalazione rappresenta una utile aggiunta alla conoscenza dell'ittiofauna di questa località-tipo del Cretaceo appenninico ed aiuta a dettagliare le caratteristiche proprie dell'ambiente marino nel quale si sedimentarono le celebri radiolariti del cosiddetto "livello Bonarelli". Particolare rilievo viene dato alla mancanza, nelle medesime radiolariti, di resti di squali carnivori predatori, quali Cretoxyrhina e Squalicorax, i cui fossili non risultano solitamente associati a quelli di Ptychodus, indicando come questo squalo durivoro abitasse un ambiente bentonico nettamente diverso dal mare aperto caratteristico dei grandi selacei predatori cretacei.
En
This study reports the presence and paleo-environmental significance of specimens of fossil teeth pertaining to the extinct Ptychodus decurrens Agassiz 1839 hybodontiform sharks from the Cenomanian (Upper Cretaceous) bituminous limestone outcroppings in the area of the Furlo Pass, Pesaro, central Italy. This provides a useful addition to knowledge of the fossil fauna of this locality, and helps to detail the characteristics of the sedimentation environment of the famous radiolarites of the so-called "Bonarelli level". The presence of remains of Ptychodus decurrens in the radiolarites of the Bonarelli level provides solid confirmation that this fauna was characteristic of a tropical-littoral benthic environment. This environment also provided abundant livelihood for durophagous fish species, in the form of lamellibranchs and thick-shelled gastropods that were typical of the Cretaceous, near-littoral, benthos. Indeed, the ibodonts are always associated with their prey, as the large lamellibranchs that were typical of the Cretaceous period (as well as the pycnodons, which were also components of the Bonarelli level fauna, and which fed on small sunken molluscs). It can also be seen from the Passo del Furlo field – as almost everywhere in the North American Cretaceous – that there was a lack of fossils of the great predatory sharks in association with the Ptychodus durophagous hybodonts. This situation has been well known for many years, especially in the deposits related to the sedimentary activity of the Western Inner Canal. This demonstrates the real division between the marine pelagic environments, which were infested by large predators (both fish, and, above all, reptiles), and the littoral environments, where the great selaceans were specialised in durofagal predation.

DOI Code: 10.1285/i15910725v40p41

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