How do wombats poop? Scientists get to the bottom of the mystery | Science

Humans may be fascinated by cubes, but only one animal poops them: the bare-nosed wombat. This furry Australian marsupial crowds out nearly 100 six-sided droppings every day – an ability that has long mystified scientists. Now, researchers say they have discovered how the wombat intestine creates this exceptional excrement.

“This study is really good,” says Sunghwan Jung, a biophysicist at Cornell University who studies the mechanics of animal movements and was not involved in the research. This shows, he says, that the guts of these animals “are very special.”

The bare-nosed wombat (Schizophyllum), which weighs up to 35 kilograms, lives in the grassy plains and eucalyptus forests of Australia, where it spends its nights grazing plants and its days in underground tunnels. It is a territorial animal, leaving its unusual droppings as a calling card. But how does such sharp feces come from a round anus?

To get to the bottom of the mystery, scientists dissected a wombat that had died after being hit by a car. They examined the intestines and found they contained two grooves where the guts are more elastic, which the team first reported in 2018.

In the new study, the researchers dissected two more wombats and tested the muscle and tissue layers of the guts, finding regions of varying thickness and stiffness. They then created a 2D mathematical model to simulate how regions expand and contract with digestion rhythms. The intestinal sections contract over several days, squeezing the poo as the intestine extracts nutrients and water from the feces, the team reports today in the aptly titled journal Soft matter.

The more rigid parts are “like a rigid rubber band -[they’re] will contract faster than soft regions, ”said David Hu, a biomechanics researcher at the Georgia Institute of Technology and study author. The softer intestinal regions slowly squeeze and mold the last corners of the cube, the team found. In other mammals, the wave peristalsis of the intestinal muscles is consistent in all directions. But in the wombat, the grooved tissue and irregular contractions over many cycles form firm, flat cubes.

That leaves only one mystery: why wombats developed cubic poo in the first place. Hu speculates that, because animals climb rocks and logs to mark their territory, flat droppings are not as likely to roll off those high perches.

As for what the world is supposed to do with this new information, Hu admits it “won’t replace the way we make plastic.” But the wombat strategy could help engineers design better ways to shape precious or sensitive materials, he says.

In the meantime, Hu also believes the knowledge could help researchers breed captive wombats. “Sometimes their feces are not as cubic as the [wild] those, ”he said. The more square the poop, the healthier the wombat.