The cubic  fecal conundrum

Understanding how the Australian marsupial, the wombat, somehow manages to extrude almost cubic feces could improve our knowledge of fluid dynamics and perhaps even suggest new approaches to manufacturing processes involving soft materials.

Animals produce their feces in a wide range of shapes and forms from the two-stage droppings of rabbits to the classic cow pat. The hydrodynamics of feces formation is perhaps one of the less romantic areas of science, but Patricia Yang of Georgia Institute of Technology and her colleagues point out that there is currently no consensus in science of the almost ubiquitous process of defecation. This is despite such medically important conditions as gastrointestinal infection, inflammatory bowel conditions, incontinence, and, of course, the vast industry that is agriculture where feces are both an important waste product and a utility in the form of fertiliser.

While the shape and form of feces may seem a trivial matter, the bowel movements of the wombat present a puzzle. Their feces emerge, not as crimped cylinders as is the wont of many animals but with flat sides that give them an odd, almost cubic appearance. Yang and her colleagues, who also study the hydrodynamics of the substance of other bodily functions including blood and urine, have taken a close look at the digestive tract of the wombat in an effort to work out how they produce such oddly shaped feces. Cubes are not commonplace in the natural world.

Yang admits that, at first, she was skeptical of "internet" claims about the shape of wombat feces. "The first thing that drove me to this is that I have never seen anything this weird in biology," she says. "That was a mystery. I Googled it and saw a lot about cube-shaped wombat poop, but I was skeptical." The team dissected the digestive tracts of wombat cadavers recovered from motor vehicle collisions in Tasmania, Australia. The specimens were provided by Scott Carver and colleagues from the University of Tasmania. The team found that near the end of the intestine, the feces change from a fairly fluid state to a more solid form and that it is the varying elastic properties of the wombat's intestinal wall that leads to this solid state forming as cube-like feces.

"We currently have only two methods to manufacture cubes," says Yang. "We mold it, or we cut it." She adds that following the wombat intestinal approach could lead to a third manufacturing technique for producing cubes of material for whatever purpose. It should be possible to make a cube with soft tissue instead of just molding or cutting it to shape.

There remains one unanswered question. Why? The team suggests that because wombats like to stockpile their odiferous feces in order to communicate through scent and mark territory, cubic stools are less likely to roll away allowing a more prominent pile to be accumulated on a single spot.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.