Australidelphia is a superorder of marsupials encompassing about three-quarters of all living marsupial species, including all those native to Australasia and one South American species, the monito del monte. Australidelphia's lineage emerged in South America, with genetic evidence (retrotransposon insertion sites) indicating that the South American monito del monte is sister to all other members of the superorder, unlike other American marsupials, which belong to the Ameridelphia.
Within this superorder, the Australian members form a distinct group (clade) named Eomarsupialia, though their internal relationships (branching order) have yet to be determined. Studies suggest that the Australidelphia originated in South America alongside other major marsupial groups. The Eomarsupialia likely dispersed to Australia via Antarctica in a single event after their divergence from their sister group, the Microbiotheria.
Phylogeny
The following cladogram is a phylogeny of Australidelphia based on the work of May-Collado, Kilpatrick & Agnarsson 2015, with extinct clades from Black et al. 2012.
↑Black; etal. (2012). "The Rise of Australian Marsupials: A Synopsis of Biostratigraphic, Phylogenetic, Palaeoecologic and Palaeobiogeographic Understanding". Earth and Life. Springer Netherlands. pp.983–1078. doi:10.1007/978-90-481-3428-1_35. ISBN978-90-481-3427-4.