Modern Australian Marsupials are generally held to be a distinct evolutionary lineage, distinct from South American Marsupials. All modern Australian and New Guinean Marsupials are placed in a single group, the Eomarsupialia. These, along with a single South American species, the Monito del Monte (Dromiciops gliroides), are placed in the Australidelphia, one of two Marsupial Superorders, the second being the Ameridelphia, which includes all other Marsupials (and which is probably paraphyletic). Marsupials are thought to have originated in the Americas, and spread to Australia via Antarctica in the Late Cretaceous or Paleocene, probably in a single event, with all Eomarsupials descending from a single Australidelphian species that made the journey.
In a paper published in the journal Naturwissenschaften on 5 August 2012, Robin Beck of the School of Biological, Earth and Environmental Sciences at the University of New South Wales and the Department of Mammalogy at the American Museum of Natural History, describes a single calceneus (heal bone) from the Tingamarra Local Fauna of Queensland, which he interprets as being from a Ameridelphian Marsupial.
The Tingamarra calceneus in (a) dorsal, (b) distsal and (c) oblique views. Beck (2012).
Beck suggests that if this interpretation is correct then it suggests that Marsupials did not reach Australia in a single event, but that there may have been some degree of exchange between Australian and South American faunas before the breakup of Gondwana between 28 and 41 million years ago.
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