How do wombats make cube-shaped droppings?
The shape begins inside the intestine, not when the droppings land on the ground.
An unusual result of digestion
Wombats are burrowing marsupials that feed primarily on tough grasses and other vegetation. Food takes a long trip through their digestive system, where water is removed from the remaining material. By the time it reaches the end of the intestine, the material is comparatively dry and able to hold a defined shape.
The surprising role of the intestine
Researchers investigating the famous cubes found that different parts of the wombat intestine stretch by different amounts. Its contractions and variations in wall elasticity help mould the material into shapes with relatively flat sides and corners. The cubes are not cut or pressed into shape outside the body; the process is physiological.
What the cubes might be good for
Wombats use droppings to communicate through scent and often deposit them on prominent objects such as rocks or logs. A cube is less likely than a round pellet to roll away from an elevated surface. That possible advantage is intriguing, although the precise evolutionary history of the shape is difficult to prove. The better-established conclusion is how the distinctive geometry forms.
External references are provided for exploration; Curio Hour’s explanation is written separately.