The bare-nosed wombat (Vombatus ursinus) is an herbivorous Australian marsupial, renowned for its cubic feces. However, the ability of the wombat’s intestine — which is approximately 10 m long, or 10 times the length of a typical wombat’s body — to sculpt flat faces and sharp corners in feces is poorly understood. In a new experimental and numerical study, published in the journal Soft Matter, biologists discovered that the cross-section of the wombat’s intestine exhibits regions with a two-fold increase in thickness and a four-fold increase in stiffness, which facilitates the formation of corners by contractions of the intestine.
“Bare-nosed wombats are renowned for producing distinctive, cube-shaped poos,” said lead author Dr. Scott Carver, a wildlife ecologist in the Department of Biological Science at the University of Tasmania.
“This ability to form relatively uniform, clean cut feces is unique in the animal kingdom.”
“They place these feces at prominent points in their home range, such as around a rock or a log, to communicate with each other.”
“Our research found that these cubes are formed within the last 17% of the intestine.”
Through a combination of laboratory testing and mathematical models, Dr. Carver and colleagues found that there are two stiff and two more flexible regions around the circumference of the wombat intestine.
The combination of drying out of the feces in the distal colon and muscular contractions forms the regular size and corners of the feces.
“The discovery highlights an entirely new way of manufacturing cubes — inside a soft tube — and the results could be applied to other fields including manufacturing, clinical pathology and digestive health,” Dr. Carver said.
“Cube formation can help us understand the hydration status of wombats, as their feces can appear less cubed in wetter conditions.”
“It also shows how intestinal stiffening can produce smooth sides as a feature of pathology.”
“Now we understand how these cubes are formed, but there is still much to be learned about wombat behavior to fully understand why they evolved to produce cubes in the first place.”
Patricia J. Yang et al. 2021. Intestines of non-uniform stiffness mold the corners of wombat feces. Soft Matter 17: 475-488; doi: 10.1039/D0SM01230K