Scientists Solve Darwin's 'Strange Animal' Mystery

After nearly 200 years, scientists have finally solved an evolutionary mystery that began with Charles Darwin, and involves a group of mammals he described as the "strangest animals ever discovered," according to a new study.

Published in the journal Nature, the findings are based on fossil protein sequences, which allow researchers to peek back in time up to 10 times farther than they can with DNA.

Until now, South America's native ungulates, or hooved mammals - the last of which disappeared only 10,000 years ago - were considered to be related to elephants and other ancient African species. But new research shows that is not the case.

In actuality, these strange animals are tied to mammals like horses, rhinos and tapirs (perissodactyls). This makes them part of Laurasiatheria, one of the major groups of placental mammals.

"Fitting South American ungulates to the mammalian family tree has always been a major challenge for paleontologists, because anatomically they were these weird mosaics, exhibiting features found in a huge variety of quite unrelated species living all over the place," Ross MacPhee, who was involved in the study, said in a statement. "This is what puzzled Darwin and his collaborator Richard Owen so much in the early 19th century."

"With all of these conflicting signals, they couldn't say whether these ungulates were related to giant rodents, or elephants, or camels - or what have you," he added.

The problem was that bone DNA did not survive over the years due to South America's warm, wet conditions. So they turned to collagen - a structural protein found in all animal bones that proved more long-lasting.

Scientists analyzed 48 fossils of Toxodon platensis andMacrauchenia patachonica, the very species whose remains Darwin discovered 180 years ago in Uruguay and Argentina. They compared the collagen to a wide range of living and a few extinct mammals to properly place the creatures on the mammal family tree.

"By selecting only the very best preserved bone specimens and with various improvements in proteomic analysis, we were able to obtain roughly 90 percent of the collagen sequence for both species," added lead author Frido Welker. "This opens the way for various other applications in paleontology and paleoanthropology, which we are currently exploring."

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