Reassessment of a large lamniform shark from the Upper Cretaceous (Santonian) of Italy

To date, only a few partially articulated chondrichthyan specimens are known from the Upper Cretaceous
marine fossil record of northern Italy. Here, we re-evaluate the taxonomic status and geological age of
selachian remains originally discovered during the 19th century from the Castellavazzo locality. The
described specimen is largely embedded in matrix with minute exposure of joined and moderately
deformed sequentially stacked vertebral centra. Computed tomography (CT) image-data obtained of the
specimen enabled the identification of potential cranial-cartilage elements located in close proximity to
teeth and are here interpreted as remnants of the jaws. Based on tooth and vertebral morphology the
specimen is in all likelihood an adult lamniform shark with a measured 3.5 m length. Using ordinary
least-squares regression analysis (OLS) and proportion-based calculations, we estimated a total-length
(TL) of 596.27 and 632.5e672.64 cm respectively. We prefer the size estimation derived through OLS
bivariate regression; however, in the present analysis, reliance on a small sample size (n ¼ 11) and evidence
for differential scaling between taxa impose limitations on the precision of our size prediction.
Planktonic foraminifera examined from the surrounding matrix of the slab preserving shark vertebral
centra and teeth indicate a Santonian age (Dicarinella asymetrica zone). Although, the specimen could not
confidently be assigned beyond the ordinal-level, the sheer centrum size, gross dental morphology, and
depositional environment, are indicative of a pelagic apex-predator comparable to coeval lamniforms,
with a specific resemblance towards cretoxyrhinids, reported from elsewhere along the peri-Tethyan
shelf of Europe and Western Interior Seaway of North America. Finally, the re-emergence of this historical
specimen, here re-described using cutting-edge techniques, is of great importance as it contributes
to the otherwise poor record of extinct lamniform shark skeletons.