Odd Evidence

Wombats Really Do Produce Cube-Shaped Droppings

Bare-nosed wombats produce roughly cubic droppings. The cause is not a square exit, as often claimed, but variation in the stiffness of the intestinal wall, which shapes the faeces during the final stretch of the gut.

The claim Wombats produce cube-shaped poop, and they do it because they have square-shaped anuses.
Confirmed Reliable evidence supports the central claim.

Confirmed by direct study of wombat intestinal tissue. The mechanism — regional variation in gut wall elasticity — was characterised in peer-reviewed work published in 2018 and 2021.

Basis 2 peer-reviewed

The claim is true

Bare-nosed wombats produce faeces with flat faces and distinguishable corners. They are not perfectly geometric — the edges are rounded and definition varies — but “cube-shaped” is a fair description rather than an exaggeration.

The animals deposit them on rocks and logs, apparently as territorial markers. Cubes are less prone to rolling off, which is the most commonly proposed functional explanation, though the fitness benefit itself is less firmly established than the shape.

The explanation attached to this fact online is almost invariably that wombats have square anuses. They do not. The shaping happens well before the exit.

The 2021 study examined wombat intestinal tissue and found that the final section of the gut is not uniformly elastic. Two regions of the wall are relatively stiff and two are relatively flexible. As the very dry faecal matter passes through, the flexible regions stretch and the stiff regions do not, and the material is moulded into a cross-section with flat faces and corners.

Two conditions make this possible. Wombat digestion is exceptionally slow — the transit can take up to around two weeks — and the resulting matter is extremely dry by the time it reaches the shaping section. Wet material would not hold an edge.

Why the verdict is Confirmed

The phenomenon is directly observed and the mechanism has been characterised in peer-reviewed work using actual tissue rather than inference. The frequently attached explanation about anatomy at the exit is wrong, but the headline claim itself holds.

Sources

  1. peer reviewed
    Yang, P. J. et al. — 'Intestines of non-uniform stiffness mould the corners of wombat faeces', Soft Matter Characterises the two stiff and two flexible regions in the wombat intestine.
  2. peer reviewed
    Yang, P. J. et al. — American Physical Society Division of Fluid Dynamics, conference presentation, 2018 First public presentation of the dissection findings.

Corrections

  • An earlier version described the droppings as 'perfect cubes'. They are approximately cubic with rounded edges, and the degree of definition varies with hydration. Corrected.

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