[2] The cladogram below, based on a 2016 study, shows the phylogenetic relationships of the white-bellied fat-tailed mouse opossum.

The tail becomes noticeably thicker, especially at the base, during the autumn, when the animal lays down fat reserves in preparation for winter.

[6] The white-bellied fat-tailed mouse opossum is found in southern Peru and south-western Bolivia, in the northernmost regions of Chile, and along the eastern slopes of the Andes mountains in western and central Argentina.

It generally inhabits rocky environments with little plant cover, but can be found in dry forest or thorn scrub.

[6][8] White-bellied fat-tailed mouse opossums are nocturnal animals with good climbing abilities, although they prefer to spend most of their time on the ground.

[7] However, phylogenetic analysis shows that the species' closest relatives are probably the elegant, common, and Tate's fat-tailed mouse opossums, all of which also inhabit arid environments.

Although fossils are known only from the Holocene, estimates for the divergence of the species from its closest relatives range from 2.2 to 6 million years ago.