Taphonomy and Paleoenvironmental Insights of a Late Miocene Armadillo Carapace (Xenarthra, Dasypodidae) in the Solimões Formation, Southwestern Amazonia, Brazil

The deposits of the Solimões Formation (Acre Basin), Brazilian Amazonia, preserve a diverse vertebrate fossil assemblage. However, taphonomic studies of both the deposits and their fossil vertebrate content remain scarce. One notable example is the osteoderms of cingulates, which are relatively abundant and diverse in the South American Cenozoic record. This study describes the taphonomic signatures observed in osteoderms of a dasypodid armadillo assigned to cf. Anadasypus sp. from the Late Miocene AC64 outcrop, Solimões Formation, Acre State, western Brazilian Amazonia. Both isolated osteoderms and a sedimentary block preserving several disarticulated but spatially associated osteoderms were analyzed using a taphonomic categorization adapted from studies on modern armadillo osteoderms. This approach allowed the identification of oblique, transverse, and longitudinal fractures, bioerosion traces, and spatial arrangement patterns. The evidence best supports a low-energy fluvial depositional setting, in which the osteoderms experienced moderate trampling and minimal transport prior to burial. Paleoenvironmental conditions were reconstructed by integrating data from the associated fauna (Testudines, Crocodylomorpha, and Trichodactylidae), sedimentary structures (rhizoliths and bioturbation structures), and carbon and oxygen isotope analyses of fossil remains and associated limestone samples. These suggest a humid fluvial depositional setting dominated by C3 vegetation, with relatively stable depositional conditions.