With a front paw outstretched and its tail at an angle, the creature that fell on to wet concrete in Chicago left quite the memento mori.
Now, researchers say they have unmasked the identity of the victim, revealing the famous “rat hole” was most probably made by a squirrel.
The unusual imprint, which was labelled “Splatatouille” in a public naming contest, is thought to have been made on West Roscoe Street decades ago, but gained a new wave of attention after a comedian shared a photo of it on social media in early 2024. The imprint was removed later that year when city officials decided sections of the pavement needed to be replaced because of damage.
While the unfortunate animal probably died while creating the impression – there are no tracks leading away from the imprint – a longstanding conundrum is whether the victim was a brown rat, as initially assumed.
“I think it’s an eastern grey squirrel. I think that is what the evidence most supports,” said Dr Michael Granatosky, first author of the study from The University of Tennessee, Knoxville.
Writing in the journal Biology Letters, Granatosky and colleagues report how they examined a list of 37 mammal species that had been observed in Chicago, ruling out those that were very rare or that did not have features seen in the imprint.
Among the remaining eight species were the brown rat, eastern grey squirrel, eastern chipmunk and muskrat.
With the imprint having been removed, the researchers used publicly available photographs to measure anatomical features such as the width of the head. They then took the same measurements from prepared museum skins of each of the eight candidates.
While none matched the imprint exactly, the researchers’ analysis revealed the eastern grey squirrel, fox squirrel, or muskrat had the closest measurements. The eastern grey squirrel, they added, was the most likely victim as eastern grey squirrels were more common in Chicago than the other two species.
“We therefore propose that the specimen be rechristened the ‘windy city sidewalk squirrel’ – a name more fitting of its likely origins and more aligned with the evidence at hand,” the team wrote.
Granatosky added that the spreading of the unset concrete could explain why the imprint was a little larger than would be expected for such a squirrel, while the researchers said their conclusion about the animal’s identity was backed by the concrete having been wet when the imprint was made – a situation that was more likely during the day, when squirrels tended to be active. In addition, they noted the animal appeared to have fallen from a height – an idea further supported by reports of nearby trees.
While the imprint showed no sign of a bushy tail, the researchers said that was not surprising, as fine-scale details such as hairs were best preserved in a very fine silt rather than concrete.
Granatosky added that the study, while somewhat frivolous in topic, not only highlighted the power of science to tackle all manner of questions, but revealed how difficult it could be to interpret traces left behind by organisms – a cornerstone of palaeontology.
“When we step in mud, or concrete in this case, things spread out, things move, there are many different layers within the track, and so it’s a hard science,” he said.
