What is "microbiotheria"

Microbiothera is an order that encompasses one family, Microbiotheriidae, and is represented by only one extant species, the monito del monte, and a number of extinct species known from fossils in South America, Western Antarctica, and northeastern Australia.

Although once thought to be members of the order Didelphimorphia (the order that contains the Virginia opossum), an accumulation of both anatomical and genetic evidence in recent years has led to the conclusion that microbiotheres are not didelphids at all, but are instead most closely related to the Australasian marsupials; together, the microbiotheres and the Australian orders form the clade Australidelphia.