Palaeodiet reconstruction of Palaeogene rodents from the Shapaja Section (Tarapoto, Peru) with dental microwear textures

Caviomorphs, or Neotropical hystricognaths, are taxonomically and ecologically diverse rodents with varied feeding habits. The earliest occurrence of the group dates back to the end of the Eocene in Peru, but the trophic ecology of these early caviomorphs and its impact on the evolution of the group are poorly understood. To shed light on the ecology of Palaeogene caviomorphs, we applied a method of dental microwear texture analysis (DMTA) to rodent teeth from the Shapaja sedimentary sequence (Tarapoto, San Martín, Peruvian Amazonia). Several fossil-bearing levels were found within this upper Eocene-lower Oligocene section, including an interval marking the Eocene-Oligocene transition (EOT). We compared the dental microwear textures of 119 fossil specimens representing 11 taxa from distinct levels of the Shapaja section with those of a reference set of 858 recent wild caviomorph specimens, divided into 11 dietary categories. Our results indicate different palaeoecologies for Shapaja caviomorphs depending on the levels and ages considered. We find i) taxa with a tendency toward diets composed of soft elements and ii) other taxa including harder or more abrasive materials. This indicates a variety of resources available in the environment as well as distinct dietary strategies among the rodents studied. This disparity in feeding behaviour persisted throughout the Eocene part of the section, as well as in the lowermost Oligocene levels studied. In contrast, a trend toward a generalist hard-element-based diet is observed in the four taxa from the most recent (earliest Oligocene) and richest level, which could be a response to a local aridification.