Marsupial moles spend most of their time underground, coming to the surface only occasionally, probably mostly after rains.
They are blind, their eyes having become reduced to vestigial lenses under the skin, and they have no external ears, just a pair of tiny holes hidden under thick hair. They do not dig permanent burrows, filling the tunnel in behind them as they move.
The head is cone-shaped, with a leathery shield over the muzzle, the body tubular, the tail a short, bald stub. They are between 12 and 16 cm long, weigh 40 to 60 grams, and are uniformly covered in fairly short, very fine pale cream to white hair with an iridescent golden sheen. Their pouch has evolved to face backwards so that it does not fill with sand, and contains just two teats, so that the animal cannot bear more than two young at a time.
The mystery was not helped by the complete silence of the fossil record. On the basis that marsupial moles have some characteristics in common with almost all other marsupials, they were eventually classified as an entirely separate order: the Notoryctemorphia. Molecular level analysis in the early 1980s showed that the marsupial moles are not closely related to any of the living marsupials, and that they appear to have followed a separate line of development for a very long time, at least 50 million years. However some morphological evidence suggests that they may be related to bandicoots.
One suggestion advanced was that the Miocene
marsupial mole used its limbs for swimming rather than burrowing, but the mainstream view is that it probably specialised in burrowing through a thick layer of moss, roots, and fallen leaf litter on the rainforest floor, and thus, when the continent began its long, slow desertification, the marsupial moles were already equipped with the basic tools that they now use to burrow in the sand dunes of the Western Australian desert.