A new ichnospecies of Machichnus Mikuláš et al., 2006 from the Quaternary of Northeastern Brazil: insights into rodent interactions with extinct megafauna in natural tank and cave deposits

Gnaw traces on megafaunal skeletal remains provide valuable insights into trophic niches and paleoecological conditions. While such traces are typically observed on bones, reports of traces on teeth are rare. In this study, we document a gnawing trace fossil on a tooth of a very young individual of Eremotherium laurillardi and two bone fragments of indeterminate mammals recovered from the Quaternary deposits of the Brazilian Intertropical Region (BIR). Stereomicroscopical analyses, measurements, and comparisons identified these trace fossils as belonging to an ichnospecies of Machichnus, which is characterized by shallow, paired U-shaped grooves. The studied trace fossils are identified as a new ichnospecies of Machichnus, Machichnus rodicus isp. nov., based on the reduction in the size of its grooves toward its edges. The rectangular shape pattern and width of studied tooth impressions are comparable only with the rectangular-shaped incisors of Kerodon rupestris among known BIR’s rodents and lagomorphs. Therefore, Kerodon rupestris represents the most plausible tracemaker. These findings represent the first indirect evidence of small-sized rodents in the Lagoa da Pedra tank and the Gruna das Três Cobras cave, highlighting interactions between these animals and megafauna carcasses while suggesting dry environment conditions during the Quaternary of the BIR.