Marsupial moles are a family (Notoryctidae) of cladotherian mammals of the order Notoryctemorphia. They are rare and poorly understood burrowing mammals of the deserts of Western Australia, with an ancestry going back 20 million years or so. Once classified as monotremes, they are now thought to be marsupials. Their precise classification was for long a matter for argument, but there are considered to be only two extant species: The two species are so similar to one another that they cannot be reliably told apart in the field.