The mystery of how, and why, wombats produce cubic poop
Wombat poo has mystified scientists for years. The shy Australian marsupial is unique for being the only animal in the world to produce cubic poo. A team of researchers has finally uncovered exactly how this quiet animal produces its square feces, and the discovery could lead to novel manufacturing techniques.
Poo comes in a variety of shapes, however the cubed dung of wombats is unique in the animal kingdom. Scientists have long wondered how this freakish feces is created. We can say for sure it is not because the animal's have square anuses, but apart from that this has remained quite the odd biological mystery.
"The first thing that drove me to this is that I have never seen anything this weird in biology. That was a mystery," says Patricia Yang, a mechanical engineer from Georgia Institute of Technology, who became fascinated with how this oddly-shaped poop was created. "I didn't even believe it was true at the beginning. I Googled it and saw a lot about cube-shaped wombat poop, but I was skeptical."
Yang and colleagues joined forces with an Australian biologist from the University of Tasmania to try and solve this mystery. The researchers obtained two dissected intestinal tracks from wombats that had been euthanized after suffering injuries from motor vehicle accidents.
Wombats have an extraordinarily slow digestive process. It can take anywhere from eight to eighteen days for food to completely pass through its very long digestive system, however the new research revealed that the cubic shape of its dung isn't formed until it reaches the final parts of the intestine. The feces stays in a relatively liquid state until it reaches the final 8 percent of the intestine where it begins to shape into small cubes.
"This shape change was due to the azimuthally varying elastic properties of the intestinal wall," the researchers write in an abstract, recently presented at the Annual Meeting of the APS Division of Fluid Dynamics. "By emptying the intestine and inflating it with a long balloon, we found that the local strain varies from 20 percent at the cube's corners to 75 percent at its edges. Thus, the intestine stretches preferentially at the walls to facilitate cube formation."
Of course it isn't unreasonable to be wondering why these animals evolved such a sophisticated way to produce cubed poo, when no other animal in the world found the need to do the same. Wombats have notoriously bad eyesight, so they communicate using scent markings. The animal's poo frequently acts as territorial markers letting other wombats know who runs a given burrow.
It is hypothesized that because of the importance of poo as a communicative tool, the animal evolved the cube-shaped excretion as a way to efficiently pile up structures of droppings. After all, you couldn't exactly build a large pile out of round droppings as effectively as you could if it were square blocks.
The new research is not just an academic scat investigation either, it may also render quite the pragmatic outcome. Yang suggests that this method could be applied to our current manufacturing processes.
"We currently have only two methods to manufacture cubes: We mold it, or we cut it. Now we have this third method," says Yang. "It would be a cool method to apply to the manufacturing process -- how to make a cube with soft tissue instead of just molding it."
The new research was presented at the 71st Annual Meeting of the APS Division of Fluid Dynamics.