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Up in the Trees

By sequencing an extinct giant ground sloth, researchers have found that tree-dwelling sloths evolved twice, independently.

Researchers led by McMaster University's Hendrik Poinar isolated DNA from a 12,880-year-old Mylodon darwinii bone fragment from a museum collection that was originally uncovered in the Patagonia region of Chile. As they report in the Proceedings of the Royal Society B, Poinar and his colleagues were able to generate a mitogenome for M. darwinii with an average depth of 99X. They also enriched more than 15 kilobases of sequence data from seven nuclear exons.

With this data, they placed M. darwinii on the xenarthran phylogenetic tree as a sister group to modern two-fingered sloths, which live in trees, and noted that the two split some 22 million years ago. This finding, they add, supports the diphyly of the two modern sloth lineages. The giant ground sloth went extinct about 10,000 years ago. 

"Our study confirms the convergent evolution of the two, tree dwelling modern sloths from two distinct lineages of extinct giant ground sloths," Poinar says in a statement. "This means tree-living evolved independently, twice, which is remarkable."