Taphonomy and paleoecology of mammals preserved in swampy deposits (Formosa Province, Argentina): new light on a key environmental context for the evolution of Quaternary vertebrates in Southern South America

Quaternary continental deposits of South America are characterized by the abundance and diversity of vertebrate remains preserved in different environmental contexts. However, the studies focused on interpreting the origin of the assemblages are scarce. The taphonomic features of the mammal specimens from the Rio Bermejo Formation, Formosa Province (Argentina), are analyzed. The bearing levels belong to the Upper Pleistocene-lower Holocene, and were interpreted as swampy deposits that filled channels of the ancient Bermejo River, an environmental context little evaluated from the taphonomic point of view. The assemblage includes Xenarthra, Notoungulata, Carnivora, Artiodactyla and Proboscidea. The evidence suggests that the assemblage is composed by specimens preserved in the place of death or close to it, with short time of subaerial exposure and little or no transport. After burial, the specimens were also affected by diverse processes directly related to the swamp deposits where they were buried. In this case, the taphonomic evidence, along with the sedimentary characteristics of the bearing levels allowed the recognition of the channel-fill mode for this assemblage. Also, this study provides new information for an area that was very important in the evolution of vertebrates in Northeastern Argentina since the Late Pleistocene.