Large deadfalls of the ʻginsuʼ shark Cretoxyrhina mantelli (Agassiz, 1835) (Neoselachii, Lamniformes) from the Upper Cretaceous of northeastern Italy. (June 2019) - Amalfitano, Jacopo
Abstract: Cretoxyrhina mantelli was a large pelagic lamniform shark geographically widespread during the Late Cretaceous, and well known because of several nearly complete skeletons from the Western Interior Seaway of North America. Here we report 15 partial skeletons belonging to lamniform sharks from the 'lastame' lithozone of the Upper Cretaceous Scaglia Rossa Formation of the Lessini Mountains (northeastern Italy). Seven partial but articulated skeletons include tooth sets that allow a confident attribution to Cretoxyrhina mantelli based on dental morphologies. We review the taxonomic history of C. mantelli, evidencing that the taxon was erected by Agassiz (1835) and tracing back four of the original syntypes. Based on calcareous plankton biostratigraphy, the rock in which the Italian skeletal remains are embedded is constrained to the middle-upper Turonian. Total length estimates of the specimens suggest that the sample includes the largest specimen of Cretoxyrhina mantelli (615–650 cm estimated total length) known to date. The placoid scale morphology indicates that C. mantelli most likely was a fast swimmer with a similar ecology as the extant white shark, Carcharodon carcharias . The associated skeletal elements of the specimens represent large chondrichthyan deadfalls and the cadavers decayed on the seafloor where they remained exposed for several months, as indicated by bioerosional traces, some of which are interpreted as a product of bone-eating worm activities and other bioerosional traces with Gastrochaenolites -like structure. The Cretoxyrhina mantelli remains described herein provide new information about the ʻlastameʼ vertebrate assemblage, which seemingly was strongly dominated by chondrichthyans, especially lamniform sharks. Highlights: Description of partial skeletal remains of the ʻginsuʼ shark Cretoxyrhina mantelli. Nomenclatural Remarks about the species C. mantelli. Emendation of the diagnosis of the species C. mantelli. Paleobiological and taphonomic Remarks about the deadfalls of C. mantelli. Micropaleontological analyses on the C. mantelli specimen matrix.