Trace fossils of incisor marks indicate multiple inhabitants of burrowing systems rodents (Geomyidae) in the Oligocene (Chilapa Formation) of southern Mexico

Trace fossils produced by fossorial mammals are relatively common in the North American fossil record. Yaviichnus iniyooensis consists of a system of chambers and tunnels marked by characteristic paired-groove marks. This text aims to analyze four burrows with well-preserved bioglyphs to determine whether one or more individuals produced them. The burrows were found in the Chilapa Formation (early Oligocene), which outcrops on the outskirts of Santiago Yolomécatl town, northwestern Oaxaca. Bioglyphs are visible on the external surfaces of the tunnel casts. These marks are short, straight, and paired, and are attributable to the incisor marks of Gregorymys spp. They may have been produced during the same ecological period. Analysis of the measurements of the width of these paired marks revealed two distinct groups: one ranging from 2.2 to 3.2 mm (mean 2.95 mm; n = 12) and another ranging from 3.4 to 5.3 mm (mean 3.99 mm; n = 31). A Mann-Whitney U test indicated statistically significant differences between the median widths of the groups. The presence of two different groups of incisor marks within a single burrow system suggests that multiple individuals were the producers. This supports the hypothesis that several individuals of Gregorymys veloxikua and G. mixtecorum were the attributable producers of Yaviichnus iniyooensis. The most plausible explanation is that burrows were reused by specimens of both species of Gregorymys, possibly linked to aridity conditions and non-solitary behaviour.