Floodplain taphonomic mode of early miocene vertebrates of Southern Patagonia, Argentina

Abstract

A continental assemblage of fossil mammals from the Santa Cruz Formation (early Miocene, Burdigalian) recovered from the coast of the Santa Cruz Province (Anfiteatro locality), Argentina, was evaluated taphonomically. Due to its stratigraphic position and age (~ 17.5 Ma), the fossiliferous level corresponds to the lower section of the Estancia La Costa Member (lower part of the Santa Cruz Formation). The Anfiteatro assemblage (Santacrucian South American Land Mammal Age) is dominated by mammals, but some birds and carnivore coprolites were also recorded. The recorded taphonomic features and the sedimentological interpretation suggest that the bone remains were preserved in a floodplain related to a fluvial system influenced by volcaniclastic input. The assemblage was interpreted as a result of death of mammals over a short period of time. The residence time of carcasses on the surface was variable. Although most bones were quickly buried, the exposure was sufficiently long for the disarticulation and scattering of different skeletal components and the agency of other processes (e.g., trampling, weathering). The loss of skeletal elements is linked to the action of water flows generated in the plain, during overbank floods or rainfalls, which mobilized those elements more susceptible to transport. After burial, the specimens were affected by diagenetic processes (e.g., soil corrosion, infilling, impregnation, deformation). The taphonomic evaluation of the Anfiteatro locality provides a framework for the analysis of other fossil assemblages with similar features worldwide..