Why does the female wombat possess a backward-facing pouch (marsupium) unlike other marsupials?

This orientation prevents soil, stones, and debris from being scraped directly into the pouch while digging.

The specialized structure of the female wombat's marsupium, oriented towards the rear rather than forwards like in kangaroos or wallabies, is a direct evolutionary adaptation to its lifestyle as a primary excavator. Since wombats spend considerable time and energy digging extensive burrow systems and manipulating abrasive soil, their movements frequently churn up dirt and small particles. If the pouch opened forward, the constant action of digging with the front paws and kicking debris backward would inevitably force stones, dirt, and dust directly onto the delicate, developing joey housed within. The rearward opening acts as a crucial protective measure, ensuring that as the mother manipulates the environment, the contents of the pouch remain clean and shielded from environmental abrasives.