Taphonomy of Oligocene teleost fishes from the Outer Carpathians of Poland

Abstract

The Oligocene ichthyotaphocoenoses from the Outer Carpathians of Poland are dominated by skeletons of actinopterygian (only teleost) fishes. Their taphonomy was studied in six localities of the Menilite-Krosno series (Błażowa, Jamna Dolna 1, Jamna Dolna 2, Rudawka Rymanowska, Wola Czudecka, Wujskie). Over 1700 specimens of variably complete fish skeletons, representative of 20 actinopterygian families, were studied. The taphonomic analysis of the skeletal disarticulation and its pattern, deformations of the vertebral column (curved, broken), arrangement of jaws and fins, the spatial array of skeletons with regard to the embedding sediment, as well as identification of unusually preserved specimens, indicate that all of the ichthyotaphocoenoses have resulted from a long-term accumulation of fish carcasses at the burial place, at a very low sedimentation rate, under anoxic conditions in, and above, the sediment/water interface. Two assemblages from the Tylawa limestone Horizon have acquired their unusually good preservation state due to the penetration of calcium carbonate into soft tissues of corpses at the burial place. In other deposits (shales, marls) the fish skeletons are more or less disarticulated as a result of decay in a calm environment. each of the ichthyotaphocoenoses displays some features indicative of mass mortality events (e.g. high density of individuals, the presence of individuals with jaws agape, high number of juveniles); none of them has a set of features indicating it unequivocally. The cause and/or conditions of death were not the same for all individuals. Only some individuals died instantaneously during mass mortalities, whereas the majority died over a period of time as a result of senility, diseases, or other circumstances. All of the ichthyotaphocoenoses show features typical of both necro- and thanatocoenoses. The associated flora and fauna, e.g., amphipods, land-derived dragonflies and bird feathers, indicate that the taphocoenoses originated as a result of accumulation of biotic remains from various environments. Fishes and associated remains settled on the bottom successively, and thus their assemblages display features typical of necrocoenoses. Evidence of fish predation is reported for the first time from the Menilite-Krosno series of Poland.