Vertebrate taphonomy of Quaternary deposits in tropical fluvial environments in South America

Taphonomic models are largely derived from studies in temperate and semi-arid regions, whereas humid tropical environments remain underrepresented, particularly in South America. This study describes and interprets the taphonomic signatures of Quaternary megafauna preserved in active fluvial deposits in southwestern Mato Grosso do Sul State, Brazil, and establishes a chronological framework for these assemblages. The analyzed sites are distributed across the Apa, Miranda, and Formoso river basins, in the municipalities of Bela Vista, Bonito, and Miranda. The material comprises 142 fossil specimens housed at the Federal University of Mato Grosso do Sul in Mato Grosso do Sul State, with complementary material from the “Pedro Candolo” Museum of Paleontology in São Paulo State. Taxonomic identification was based on morphological criteria, and taphonomic analysis considered fracture patterns, abrasion, weathering, and bioerosion. Taxonomic composition includes Xenarthra, Proboscidea, Cingulata, Crocodylia, and Chelonia. Radiocarbon ages from the Apa River indicate an Early Holocene chronology. The fossil assemblages are composed of remains predominantly disarticulated and fragmented, with variable preservation and a high proportion of indeterminate remains. Differences in transportability indicate distinct hydrodynamic conditions, with a predominance of elements of intermediate transportability. Taphonomic features reflect deposition in open, dynamic systems, suggesting time-averaged assemblages that represent long-term depositional processes rather than synchronous ecological records.