Of all the many mysteries surrounding common wombat, it is difficult to find one as perplexing as its ability – widely recognized as unique in the natural world – to produce cube-shaped feces.
Why plump marsupials could benefit from six-faced feces is generally accepted: wombats mark their territorial boundaries with scented piles of poop and the larger the stacks, the better. With die-shaped manure, wombats increase the chances that their droppings, deposited near burrow entrances, prominent stones, raised earth and logs, will not roll. That, at least, is thought.
But the way animals produce strange-shaped blocks-and they can go up to 100 a night, presumably with some trepidation-has proved more difficult to solve. Scientists who are intrigued by the phenomena have made little progress beyond dismissing the uncomfortable suspicion that animals had square anuses.
"My curiosity was triggered when I realized that there are cubic feces," said Patricia Yang, a postdoctoral fellow in mechanical engineering at the Georgia Institute of Technology in Atlanta. "I thought it was not true in the first place."
In a new study, Yang and his colleagues had a new fissure in the problem. To gain insight into the mystery, they studied the digestive tracts of common wombats that were sacrificed after being hit by cars and trucks on roads in Tasmania.
A close inspection revealed that the vombate excrement solidified in the last 8% of the intestine, where the stool accumulated as blocks the size of long, thick sugar cubes. By emptying the intestines and inflating them with long modeling balloons, the type used to make balloon animals at children's parties, the researchers measured how the tissue stretched in different places.
In a paper to be presented at a meeting of the American Society of Physics's fluid dynamics division in Georgia, the team explains how the last section of the vombate gut does not stretch evenly, unlike the rest of the gut. When measured around the circumference, some parts give more than others. This allows the intestine to deform in such a way that it packs the stool into cubes 2 cm wide instead of the usual forms of sausage. The results were supported by tests on pig intestines that did not find such irregularities in the way they extended.
"Bowel guts have periodic stiffness, which means stiff-soft-hard-soft, along the circumference to form cubic feces," Yang said.
But the researchers have not finished work yet. To produce a poop with a square cross section, the gut circumference would need four interspersed elastic regions with four rigid regions. In this way, the rigid regions form the flat faces, while the more elastic parts allow the corners to form. The balloon tests revealed only three elastic and two more rigid parts. In an article to be published, scientists suggest that other hard, elastic pieces can only become apparent when they can inflate the intestines to a larger size. In other words, push yourself a little harder.
Yang believes that the revelation will have implications beyond the small community of researchers who admit an interest in wombat scat. Today, engineers have only two methods to make cubes: to shape or cut them, he points out. The vomiting intestines suggest that a third pathway is possible. "It would be a legal method to apply in the manufacturing process," she said.
"We can learn from wombats and, hopefully, apply this new method to our manufacturing process. We can understand how to move these things in a very efficient way. "