CHICAGO, June 6 (Xinhua) -- A pair of studies published on Thursday have shaken up the sloth family tree, overturning a longstanding consensus on how the major groups of sloths are related.

The studies indicate the three-toed sloth is more closely related to a large family that included ancient elephant-sized ground sloths, while the two-toed sloth appears to be the last survivor of an ancient lineage previously thought extinct.

"What came out was just remarkable. It blew our minds-it's so different from anything that's ever been suggested," said Graham Slater, an assistant professor of geophysical sciences at the University of Chicago who co-authored one of the papers.

Slater's study, published on Thursday in Nature Ecology & Evolution, uses a pioneering approach that uses proteins in fossils to discover evolutionary relationships, marking the first time an entire lineage has been mapped with the method.

Instead of DNA, the researchers have been looking at proteins instead. Protein molecules are sturdier, and since DNA is translated directly into proteins, they hold much of the same information.

The researchers extracted collagen from multiple fossils, analyzed it to reconstruct the sequences of amino acids, and then compared these to one another to piece together relationships between the species.

Scientists previously thought that the unau, the three-toed sloth with cute black lines around its eyes, was an outlier species that diverged early in the group's evolution. But based on the new evidence, it actually appears to be nested within a large group of different ground sloths that includes those gigantic, elephant-sized sloths.

Meanwhile, the ai, the two-toed sloth, had been classified in with a family called Megalonychidae, which includes everything from Central American and Caribbean sloths to an Ice Age-era American ground sloth. But according to the findings, two-toed sloths are actually the last survivors of a branch previously thought to be extinct, which likely split off about 20 million years ago.

The protein evidence also revealed that those extinct Caribbean sloths were the descendants of an early branch that split from other sloths around 30 million years ago.

"All of these ancient sloths must have occupied really important roles in grazing and browsing the landscape, and so they're important to understanding how these ecosystems worked," said Slater. Enditem

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