Australian Marsupials Share American Ancestor



Australia’s lovable, iconic marsupials — kangaroos, koalas, and wallabies — have their roots not in the land down under, but in a common ancestor from South America, according to a new study. 

Researchers from Munster University in Germany used genome sequencing to construct an updated marsupial family tree and the findings were not at all what they expected. 

The DNA data, published in a recent edition of the journal PLoS Biology, contradict previous assertions based on fossil data that marsupials originated in Australia and then migrated out to South America and beyond. 

Marsupials are unique because they carry their young around in belly pouches. A marsupial common ancestor split off from other mammals around 130 million years ago, but scientists have struggled to identify what species that ancestor was. 

Now, scientists are one step closer thanks to jumping genes called retroposons — genes that copy themselves and are then randomly reinserted in the genome. These gene types are rare, and when different species share them, it means the animals also share a common ancestor.

The more jumping genes two species share, the more closely they are related — and marsupials from South America and Australia share 10 genes

The Australian marsupials, however, had a few more recent jumping genes in common, proving that the South American species originated first. 

Fossil evidence puts the earliest marsupial in China. Rather than coming up from Australia, the researchers hypothesize the animals, probably a single species at the time, started in China.

This species then migrated across the former super-continent Gondwana to what is currently South America, and eventually made their way to Australia, where they diversified into the unusual animals we see today. 

Image: KayAreWhy, Flickr

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