Taphonomic patterns in the fossil record of baleen whales from the Pliocene of Piedmont, north-west Italy (Mammalia, Cetacea, Mysticeti)

The Tertiary Piedmont Basin (TPB) is located in north-western Italy and represents the western portion of a long and wide basin occupying the area that is now known as the Po Plain. Largely continuous sedimentation occurred in this basin from the early Miocene to the Pleistocene; two Pliocene marine formations are well known from this basin: Argille Azzurre and Sabbie d'Asti formations. Both these formations are rich in marine fossils including numerous cetacean specimens. We analysed the Pliocene mysticete partition of the TPB cetacean record including 55 baleen whale specimens from two museum collections to interpret the taphonomic factors influencing the preservation potential of the basin. Careful observations of bones were performed to find evidence of causes of death, floating and transport, interactions with sharks, timings of burial and whale fall activity. Analysis of preservation of specific bones (vertebrae, mandible, forelimb) was performed in order to discriminate between different mechanisms of transport in the water column or on the seafloor. We found that biostratinomic agents were active all along the basin in both the formations; these included scavenging, bottom currents and the activities of bacteria and whale fall communities. Intense shark-cetacean interactions are recorded by shark bite traces on mysticete bones. Patterns of preservation of vertebrae and loss of paired appendages are used as evidence of floating and transport on the seafloor. A mix of early and late burials is inferred on a specimen basis allowing for the characterisation of the complete biostratinomic history of each mysticete specimen. We suggest that many factors are responsible for good preservation in the TPB mysticete record; these include relative timing of burial and intensity of biostratinomic processes active prior to burial.