Monito Del Monte - Phylogeny and Biogeography

Phylogeny and Biogeography

It has long been suspected that South American marsupials were ancestral to those of Australia, consistent with the fact that the two continents were connected via Antarctica in the early Cenozoic. Australia’s earliest known marsupial is Djarthia, a primitive mouse-like animal that lived about 55 million years ago. Djarthia had been identified as the earliest known australidelphian, and this research suggested that the monito del monte was the last of a clade which included Djarthia. This implied that the ancestors of the Monito del Monte might have reached South America via a back-migration from Australia. The time of divergence between the Monito del Monte and Australian marsupials was estimated to have been 46 million years ago. However, in 2010, analysis of retrotransposon insertion sites in the nuclear DNA of a variety of marsupials, while confirming the placement of the Monito del Monte in Australidelphia, showed that its lineage is the most basal of that superorder. The study also confirmed that the most basal of all marsupial orders are the other two South American lineages (Didelphimorphia and Paucituberculata, with the former probably branching first). This indicates that Australidelphia arose in South America (along with the ancestors of all other living marsupials), and probably reached Australia in a single dispersal event after Microbiotheria split off.