Dec. 12, 2003 — Sino-U.S. scientists discovered the world's oldest fossil of a marsupial ancestor in northeastern China, according to findings released Thursday.
The discovery of the mouse-sized animal, an ancestor of the modern-day kangaroo and koala, led scientists to believe that marsupials — which carry their young in a pouch — diverged from placental mammals nearly 125 million years ago, some 50 million years earlier than researchers had initially thought, according to findings published in the journal Science.
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The largely intact fossil sheds new light on the origin of mammals and how they adapted, according to study leader Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh, Pa.
"This mammal could be the great grand aunt or uncle, or it could be the great grandparent of all marsupial mammals," said Luo in a press release.
The shape of the animal's paws indicates that it was able to climb trees, which would have enabled it to live in various habitats.
According to the researchers, the fossil reinforces the theory that Asia was one of the centers of mammalian diversification.
But in a commentary published in the same journal, other scientists caution that additional discoveries are needed to pinpoint precisely where mammals first appeared.
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