Taphonomic analysis of an articulated mysticete (Cetacea; Mysticeti) from the late Miocene Puerto Madryn Formation, Peninsula Valdés, Patagonia, Argentina.

NICOLAS FARRONI; JOSE CUITIÑO; DARIO LAZO; MÓNICA BUONO

Virtual Meeting

Otro; 9th International Meeting on the Secondary Adaptation of Tetrapods to Life in Water Virtual Meeting; 2021

Taphonomic studies of fossil cetaceans in Argentina are scarce and they were focused mainlyin odontocetes and misticetes from the Gaiman Formation (lower Miocene of Patagonia).These analyses propose different factors (i.e., paleoenvironmental, paleobiological andpaleoecological) that controlled the preservation of cetaceans. Prospecting fieldworks on thePuerto Madryn Formation (late Miocene) result in the discovery of a well-preserved andarticulated baleen whale (= Mysticeti) specimen in Peninsula Valdés, Chubut, Argentina. Thisspecimen was the focus of a taphonomic analysis with a multidisciplinary approach includingtaxonomical, sedimentological, stratigraphic and ichnological analyses, with the aim ofreconstructing the taphonomic processes and the paleoenvironmental conditions that played arole in the preservation of the specimen. The preliminary taxonomic analysis shows that thespecimen corresponds to an adult to subadult belonging to the family Balaenidae. It displaysa high degree of articulation, a low to moderate degree of fragmentation and a relatively highdegree of completeness (i.e., presence of cranial bones, tympano-periotic, mandibles, maxilla,caudal, thoracic and cervical vertebrae, ribs and a fragmented scapula). Our results suggestthat after death, the balaenid followed a brief biostratinomic route that can be summarized infour stages: A) death at sea, with an initial decomposition and positive buoyancy of thecarcass; B) internal accumulation of putrefaction gases, reorientation, loss of connectivity ofthe skeletal elements and gas loss; C) sinking and deposition in ventral-up position on theseafloor and; D) a lateral re-orientation (side-up) of the postcranial region due to physical andbiological processes. The high degree of bones articulation and association, the presence ofmandibles, the moderate fragmentation and the lack of evidence of scavenging, indicate nolateral transport on the seabed. These observations allowed us to dismiss reflotation processesof the carcass. Also, the taphonomic features (e.g., high degree of articulation, low degree offragmentation, polymodal orientation) of the associated invertebrate fossils and theichnogenera, support this interpretation. The final deposition of the whale carcass on theseafloor did not result in an ecological impact as is known for whale-fall communities’studies. Finally, the collected data indicates a low-energy shelf environment with normalmarine oxygenation, productivity and salinity conditions, characterized by a soft bottom anda low to moderate sedimentation rate. This, combined with the high bioturbation activity,resulted in a rapid burial of the carcass because of the sediment removal. Thereby, the fossildiagenetic processes allowed the final conservation of the skeleton.