Australidelphia is the
superorder that contains roughly three-quarters of all
marsupials, including all those native to
Australasia and a single species from
South America. (All other American marsupials are members of the
Ameridelphia.) Analysis of
retrotransposon insertion sites in the
nuclear DNA of a variety of marsupials has shown that the South American
monito del monte's
lineage is the most
basal of the superorder. The Australian australidelphians form a
clade, for which the name Euaustralidelphia ("true Australidelphia") has been proposed (the branching order within this group is yet to be determined). The study also showed that the most basal of all marsupial orders are the other two South American groups (
Didelphimorphia and
Paucituberculata, with the former probably branching first). This indicates that Australidelphia arose in South America along with the other major divisions of extant marsupials, and likely reached Australia via Antarctica in a single
dispersal event after Microbiotheria split off.
