*Warning: Poop in second picture ;)
Wombats are marsupials (cousins to koalas and kangaroos) native to Australia. They have specially designed body structures to produce dice-shaped poo. This is to prevent them from rolling away.
But why worry about your poo rolling away?
Apparently, they have a terrible sense of sight but a great sense of smell. So in order to find their way home in the dark, they poop on top of logs and rocks -- hence the need for the poop to stay in once place.
(EDIT: added third pic to show what they're made of at @oj1992 's request :P)