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Fossils push back origins of modern mammals

Common ancestor evolved over 200 million years ago

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2:39pm, September 10, 2014
drawing mouse-sized mammal Xianshou songae

TREE HUGGER  A newly identified mouse-sized mammal species, Xianshou songae, lived in Jurassic forests and has helped scientists redefine the mammalian family tree. 

Modern mammals’ ancestors may have emerged millions of years earlier than scientists suspected — around the time the first dinosaurs roamed the Earth.

The fossilized remains of six little tree-dwelling animals push the lineage of today’s mammals back to the Late Triassic, more than 200 million years ago, researchers report September 10 in Nature.

“That’s really, really old,” says paleontologist Robert Asher of the University of Cambridge, who was not involved with the work. Scientists had thought that the common ancestor of those animals originated sometime in the Jurassic, he says. “This is very exciting stuff.”

The newly reported fossils were found in China and belong to three new species of haramiyid, a group of extinct mammals that researchers first discovered more than a century ago. But most of the animals left behind only teeth, says study coauthor

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