Rodent indent not self-evident: a case of mistaken identity of the 'Chicago Rat Hole'

The 'Chicago Rat Hole' is a remarkable full body impression ostensibly created by a brown rat (Rattus norvegicus) crossing fresh concrete in Chicago's Roscoe Village that became a viral sensation. While the public attributed the mark to a brown rat, no formal analysis had been conducted to confirm its identity. Using clear anatomical landmarks, we compared measurements from the 'Chicago Rat Hole' to eight sympatric rodent species using univariate and multivariate analyses. Univariate tests showed no significant differences in snout-to-tail length, head width, tail-base width or third digit length between the imprint and members of the genus Sciurus (i.e. tree squirrels). Discriminant function analysis indicated a 98.67% likelihood that the 'Chicago Rat Hole' was a squirrel, with classifications split between the eastern grey squirrel (50.67%) and the fox squirrel (48.00%). Given local population densities, an eastern grey squirrel likely represents the most parsimonious species-level match. This investigation underscores the challenges of attributing a trace to the tracemaker. While we acknowledge the playful spirit of this investigation, our broader aim is to highlight that scientific inquiry begins with curiosity and observation: qualities that are not exclusive to professional scientists, but accessible to anyone with an interest in understanding the natural world.