Meet the Wombat: How This Marsupial Makes Perfect Cube-Shaped Droppings

The bare-nosed wombat (Vombatus ursinus) produces a biological oddity: cube-shaped feces. What looks like a curiosity is actually the result of specialized intestinal anatomy and long digestive processing — a solution refined by evolution to solve a real-world problem.

From Field Mystery to Scientific Explanation

Imagine a wildlife ecologist on a flat rock in southeastern Australia finding a neat stack of tiny, two-centimetre cubes. Reports of rectangular wombat droppings date at least to 1960, and for decades scientists suggested explanations ranging from oddly shaped pelvic bones to geometric anal sphincters. Each hypothesis was tested and discarded.

The CT Scans and the Breakthrough Study

In 2019, CT scans of live wombats performed by researchers at the Georgia Institute of Technology showed the anus is circular and that pelvic bones are too distant to shape the droppings. The definitive explanation arrived in 2021 with a Soft Matter paper by Patricia J. Yang, Alexander B. Lee, Scott Carver and David L. Hu.

What the Researchers Found

Dissecting three bare-nosed wombats (animals that had been humanely euthanized after vehicle collisions), the team combined histology and tensile tests to map intestinal material properties. The large intestine’s cross-section is not uniform: it alternates around the circumference between two stiffer regions and two more compliant (softer) regions. The stiffer zones were about twice as thick and roughly four times stiffer than the soft zones.

During peristalsis — rhythmic waves of contraction present in all mammals — those alternating regions deform at different rates. The stiffer segments contract more quickly while the softer segments lag. Repeating that differential deformation many thousands of times gradually sculpts round slurry into forms with edges and corners. According to the study, the cylinder-to-cube transformation occurs within the final ~17% of the large intestine and unfolds across roughly 40,000 individual contractions.

Drying Locks the Shape

Shape alone is not enough: the feces must be firm. Wombat droppings are drier than typical human feces (about 60% water versus ~80% in humans), a consequence of a very long gut and retention times of 40–80 hours. That dehydration makes the material stiff enough to hold corners once formed; in wetter conditions the cubes become less defined. Field observations suggest that droppings’ squareness can reflect digestive health.

Why Cubes? An Evolutionary Advantage

Wombats are solitary and strongly territorial. They deposit feces in deliberate latrines on conspicuous features such as rocks, logs and burrow entrances. A spherical dropping placed on a rock can roll away; a cube will not. Flat faces provide mechanical stability on uneven surfaces, keeping scent markers precisely where the animal places them. Researchers propose that this stability is the key adaptive advantage and that behavior and intestinal morphology co-evolved.

Bigger Implications

The mechanism — generating precise geometry through internal material properties and repeated deformation — has inspired ideas beyond biology. In manufacturing, it suggests new biomimetic approaches for shaping delicate soft materials without rigid molds or cutting tools. Clinically, the study highlights that intestinal wall stiffness can shape output; because wall stiffness changes with disease, fecal morphology could, in principle, become a non-invasive diagnostic clue for some gastrointestinal conditions. Observations that unhealthy captive wombats produce less cubic scat support that possibility, though human applications would require substantial further research.

In short: a unique combination of alternating intestinal stiffness, repeated peristaltic contractions, and prolonged drying produces the wombat’s cubes — an elegant example of form emerging from material properties and behavior.

When Scott Carver’s team first noticed this phenomenon during mange research, they likely did not anticipate it would yield an Ig Nobel prize, a landmark materials-science paper, and fresh perspectives on evolution, diagnostics and manufacturing. In the rocky scrublands of southeastern Australia, the wombat leaves behind cubic proof of how evolution can shape even the most intimate anatomy.