Australia: The Land Where Time Began

A biography of the Australian continent 

The authors of this paper, a team from the University of Muenster in Germany, studied the genomes of 20 marsupials from South America and Australia, concentrating on retrotransposons (retroposons) (jumping genes). The authors interpret their findings as suggesting a single group of marsupials migrated from South America to Australia, thus giving rise to all later Australian marsupials.

The conclusions in this paper have been disputed by Michael Archer, of the University of New South Wales and Jenny Graves, of the ANU. According to Archer, earlier studies have suggested the exchange of marsupials between South America and Australia was bi-directional. He said the authors failed to recognise that  Australia has been a centre of marsupial evolution. The evidence Archer refers to is the small marsupial, Dromiciops gliroides, from the rainforests of Argentina and Chile, known locally as monito del monte (little mountain monkey). See Marsupial origins. Evidence from earlier studies had found that it was distantly related to Djarthia murgonensis, the earliest known marsupial in Australia, D. gliroides is believed by Archer and others to have evolved in Australia, migrating back to South America via Antarctica, at a time when the 3 continents were joined in Gondwana, and were mostly covered with rainforest. According to Graves, D. gliroides may have migrated to Australia from South America, then returned. But it could possibly have remained in South America when its close relatives migrated to Australia. In both appearance and its genetics it appears closer to Australian marsupials than to marsupials from South America.

Sources & Further reading

1. Crew, Becky, Oct/Nov 2010, The Mystery of Australian Marsupial Origins, Cosmos Magazine
2. Nilsson, M.A., et al., 2010, Tracking Marsupial Evolution using Archaic Genomic Retroposons Insertions. DOI: 10.1371/Journal.pbio.1000436

Links

Jumping Genes Reveals Kangaroos' Origins