... And sometimes it works.

Morphology may have assigned the extinct giant ground sloth a wrong spot on the evolutionary tree, reports Matthias Hoss, a graduate student in the group of Svante Paabo at the University of Munich in Germany.

Hoss drew that conclusion from comparisons between the DNA sequences of the two living species of South American sloth and one extinct beast, Neomylodon. This slow-paced edentate roamed the steppes of Patagonia during the last ice age.

Traditionally, morphologists though Neomylodon had branched off long before the two living sloth species developed. That would have made Neomylodon's family, the Mylodontidae, closer cousins of the South American anteater and opossum than Hoss thinks they actually are.

Hoss analyzed DNA he had isolated from 13,000-year-old sloth remains and subsequently amplified with PCR. "The outcome of the genetic information differs from previous morphological information," he says. It indicates that Neomylodon was more closely related to today's two-toed tree sloth than to the modern three-toed tree sloth and that it was only a distant cousin of anteaters and opossums.

If Hoss is right, will other extinct sloths move to different places on the tree as well? Stay tuned, he says.