The bare-nosed wombat (Vombatus ursinus), which weighs up to 35 kilograms, lives in the grassy plains and eucalyptus forests of Australia, where it spends its nights grazing on plants and its days in underground tunnels. It’s a territorial animal, leaving its unusual droppings as a calling card. But how does such sharp-sided scat 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 that they contain two grooves where the guts are more elastic, which the team first reported in 2018.

In the new study, the researchers dissected two further wombats and tested the guts’ layers of muscle and tissue, finding regions of varied thickness and stiffness. They then created a 2D mathematical model to simulate how the regions expand and contract with the rhythms of digestion. The intestinal sections contract over several days, squeezing the poop as the gut pulls nutrients and water out of the feces, the team reports today in the aptly titled journal Soft Matter.

https://www.sciencemag.org/news/2021/01/how-do-wombats-poop-cubes-scientists-get-bottom-mystery