It's a biological curiosity that left scientists perplexed and fascinated the internet.
Researchers now believe they have solved one of the most fetid mysteries in the animal kingdom: how wombats produce cuboid poop.
The six-sided portions of the manures of bulky marsupials are of a unique nature. And they produce them prolifically, depositing between 80 and 100 cubes per night.
The characteristic defecation of Wombats has an important function, allowing the animals to stack their feces to mark their territory and to communicate through the smell.
The flat sides of the pellets mean that they can be placed prominently in trunks and stones without rolling out, making them more likely to attract the attention of a partner.
But scientists have always been uncertain about how wombats – which have circular anuses – shape their feces in their unusual shape. Now a team of mechanical engineers from the United States and Australian biologists believe they have eliminated any doubt.
The lead author of the study, Patricia Yang, a postdoctoral fellow at the Georgia Institute of Technology, decided to investigate whether differences in Soft tissue structures can explain their manure in a strange way.
"The first thing that led me to this is that I've never seen anything so strange in biology. This was a mystery, "said Yang, who studies the hydrodynamics of fluids including blood, processed food and urine in animal bodies.
She added, "I did not even believe it was true at first. I researched and saw a lot about cube-shaped wombat poop, but I was skeptical."
The researchers studied the digestive tracts of wombats that had been killed after being hit by road vehicles in Tasmania, Australia.
Near the end of the intestine, they found that the feces changed from liquid to solid states composed of separate small cubes. The researchers concluded that the variable elastic properties of the wombats' intestinal walls allowed the formation of cubes.
In the artificial world, cubic structures are commonly produced by injection molding or extrusion. But in nature form is extremely rare: wombats are the only known species capable of producing cubes organically.
Yang said his findings may have implications for manufacturing, as well as contribute to the scientific understanding of soft tissue transport.
"We currently have only two methods of making cubes: we shape or cut them. Now we have this third method, "Yang said. "It would be a cool method to apply in the manufacturing process – like making a cube with soft tissue rather than just molding it.
"We can understand how to move these things in a very efficient way."
Scott Carver, an Australian biologist involved in the study, added: "There is a lot of general public interest, both in Australia and internationally, about how and why wombats create cube-shaped feces.
"A lot of ideas, some more fun than others, were put forward to explain this, but until that study no one had investigated the cause. This has been a fantastic collaboration that shows the value of interdisciplinary research to make new scientific discoveries. "
The researchers will present their findings at an annual meeting of the Fluid Dynamics Division of the American Physical Society in Atlanta, Georgia this week.