The wombat is the one and only marsupial that can literally shit a brick, and we’re starting to understand how they do it:
[H]ow the animals produce the awkward-shaped blocks — and they can pass up to 100 per night, presumably with some trepidation — has proved a harder one to work out. Scientists who find themselves intrigued by the phenomena have made little progress beyond ruling out the nagging suspicion that the animals possessed square anuses.
“My curiosity got triggered when I realised that cubical feces exist,” said Patricia Yang, a postdoctoral fellow in mechanical engineering at Georgia Institute of Technology in Atlanta. “I thought it was not true in the first place.”
In a new study, Yang and her colleagues have had a fresh crack at the problem. To gain new insights into the mystery, they studied the digestive tracts of common wombats that had been euthanised after being struck by cars and trucks on roads in Tasmania.
Close inspection revealed that the wombat’s excrement solidified in the last 8% of the intestine, where the feces built up as blocks the size of long and chunky sugar cubes. By emptying the intestines and inflating them with long modelling balloons, of the sort used to make balloon animals at children’s parties, the researchers measured how the tissue stretched in different places.
In work to be presented at a meeting of the American Physical Society’s fluid dynamics division in Georgia, the team explain how the last section of the wombat intestine does not stretch evenly, unlike the rest of the intestine. When measured around the circumference, some parts give more than others. This allows the intestine to deform in such a way that packs feces into 2cm-wide cubes rather than the usual sausage shapes. The findings were buoyed up by tests on pig intestines which found no such irregularities in how those stretched.
And why would such a feature evolve in the first place?
[W]ombats mark their territorial borders with fragrant piles of poo and the larger the piles the better. With die-shaped dung, wombats boost the odds that their droppings, deposited near burrow entrances, prominent rocks, raised ground and logs, will not roll away.
The only real disappointment here is that we don’t actually have a SpongeBob SquareAnus.