Chicago Rat Hole probably made by a squirrel, study says

Researchers say the concrete impression in Chicago long known as the Chicago Rat Hole was most likely made by a squirrel, not a rat, according to a study published Wednesday in the journal Biology Letters. The imprint, which had become a local curiosity after drawing crowds to a Roscoe Village sidewalk in early 2024, was analyzed using measurements from photographs and museum specimens to identify the species that produced the rodentlike outline.

Michael Granatosky, an evolutionary biomechanics researcher at the University of Tennessee, Knoxville, led the team that treated the imprint as a modern trace fossil. The researchers collected dozens of images circulated online and measured anatomical features visible in the indentation, including snout-to-tail length and head width. They then used a list of small mammals recorded in the Chicago area and compared the imprint measurements to those of museum specimens for eight candidate species. The proportions most closely matched those of tree squirrels, specifically the eastern gray squirrel or the fox squirrel, the study concluded.

Granatosky said the evidence allows researchers to exclude a brown rat as the maker of the impression....