What was once a quirky urban mystery
On a damp stretch of West Roscoe Street in Chicago, a peculiar imprint in the concrete captured the public imagination. Dubbed “Splatatouille” in a light-hearted public naming contest, the footprint-like mark suggested something extraordinary had fallen onto wet pavement. The image spread across social media in 2024, prompting months of fascination and speculation about whether the culprit was a rodent or something else entirely.
City officials eventually removed the section of pavement for repairs, leaving behind a gap in the mystery. Now, a scientific study offers a fresh, data-driven conclusion: the imprint most likely came from an eastern grey squirrel rather than the brown rat that had first been suspected.
The researchers and their approach
The study, published in Biology Letters, was led by Dr. Michael Granatosky and colleagues from the University of Tennessee, Knoxville. The team faced a classic but vexing problem: identifying a creature based on a single, imperfect trace left in a medium that can distort details. The imprint’s lack of departing tracks and the presence of a wet concrete surface complicated straightforward identification.
To tackle the question, researchers constructed a robust comparison framework. They started with a curated list of 37 mammal species known to inhabit Chicago, systematically narrowing the field by eliminating species that were either too rare or didn’t exhibit comparable features in the footprint. The survivors included candidates such as the brown rat, eastern grey squirrel, eastern chipmunk, and muskrat—eight plausible contenders after initial screening.
How the team reached its conclusion
With the original imprint no longer accessible, the researchers relied on publicly available photographs of the scene to extract measurements. They focused on anatomical features that could be inferable from a footprint-like mark, notably the width of the head as a proxy for overall skull proportions. Those measurements were then matched against prepared museum skins of the eight candidate species, providing a data-driven basis for comparison.
The analysis did not yield an exact match to any single species, which is expected given the imperfect nature of the imprint and the abrupt, wet medium. However, the evidence pointed most strongly toward the eastern grey squirrel, the fox squirrel, or the muskrat. Among these, the eastern grey squirrel emerged as the most likely culprit, primarily because grey squirrels are more common in Chicago than the other two, making them the most plausible source of the imprint under ordinary urban conditions.
The final verdict and its playful reinvention
Based on the measurements and ecological context, the researchers proposed a lighthearted rechristening: the “windy city sidewalk squirrel.” The name nods to Chicago’s climate and the evidence at hand, while keeping in the spirit of the original meme. They also offered plausible explanations for why the imprint might appear larger than expected for a single squirrel: the concrete could have been spreading, and the surface was wet at the time of impact, factors that tend to exaggerate apparent size.
The study acknowledges a limitation: some fine-scale attributes, such as hairs or tail details, are rarely preserved in concrete. As a result, absolute certainty remains elusive. Yet the team argues that the weight of evidence supports the eastern grey squirrel as the best-supported candidate among plausible species, especially given the animal’s prevalence in the city.
Why this matters beyond a humorous moment
Though the topic may seem whimsical, the research underscores a serious scientific principle: interpreting traces left by organisms is inherently challenging. Trace fossils and field marks are snapshots of dynamic processes, often affected by the environment, the substrate, and the behavior of the animal. Palaeontologists frequently contend with similar issues when reconstructing how ancient creatures moved and interacted with their surroundings. The Chicago imprint thus becomes a teachable example of how scientists deduce identity from imperfect evidence, balancing statistical likelihood with ecological context.
As Granatosky reflects, “When we step in mud, or concrete in this case, things spread out, there are many different layers within the track, and so it’s a hard science.” The study demonstrates that even lighthearted curiosities can illuminate rigorous research methods and invite broader appreciation for the science of traces.
What’s next?
For enthusiasts and skeptics alike, the Splatatouille episode reinforces how urban wildlife continues to leave their footprints in surprising places. Future research could investigate how substrate, moisture, and height of fall influence imprint characteristics, turning a fleeting moment into a more formal case study in trace analysis.
