Permineralization as a Key Process in Vertebrate Fossilization: Insights from a Newly Discovered Cetacean Assemblage from Northeastern Italy (Venetian–Friulian Basin; Lower Miocene)

The Lower Miocene (upper Aquitanian to lower Burdigalian) marine deposits exposed at the Colle della Croce quarry (Feltre, Belluno Province, northeastern Italy) have recently yielded a rich fossil assemblage of toothed whales that complements the nearby, largely coeval historical collections from the Belluno area. Here, we present an integrated histotaphonomic study of this newly discovered cetacean assemblage by combining macroscopic, petrographic, and microanalytical techniques. All specimens show remarkable preservation of the original histological microstructures despite the common occurrence of post-mortem bone modifications, including microbial-derived microborings. Permineralization is widespread, with calcite, silica, barite, and iron sulfides infilling the osteons and lacunae. Compositional data indicate recrystallization of bone bioapatite (hydroxylapatite) into fluorapatite. Bones from glauconite-rich sandy levels are more abraded, rounded, and bioeroded, as well as harder and darker, than those from finer-grained deposits, highlighting the influence of the host sediment on fossil preservation. Despite extensive degradation at the seafloor, early and late diagenetic processes—first and foremost, permineralization—reduced bone porosity and stabilized the skeletal remains, thereby enhancing their preservation potential. Overall, these results highlight the pivotal role of diagenesis in shaping the taphonomic fate of cetacean skeletons.