The oldest microbiothere currently recognised is
Khasia cordillerensis, based on
fossil teeth from Early Palaeocene deposits at
Tiupampa,
Bolivia. Numerous genera are known from various Palaeogene and Neogene fossil sites in South America. A number of possible microbiotheres, again represented by isolated teeth, have also been recovered from the Middle
Eocene La Meseta Formation of
Seymour Island, Western Antarctica. Finally, several undescribed microbiotheres have been reported from the Early Eocene Tingamarra Local Fauna in northeastern Australia; if this is indeed the case, then these Australian fossils have important implications for understanding marsupial evolution and
biogeography. The distant ancestors of the
monito del monte, it is thought, remained in what is now South America while others entered
Antarctica and eventually
Australia during the time when all three
continents were joined as part of Gondwana. ==References==