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Fossilized shrew could be ancient human kin

This fossil is believed to be the earliest placental mammal ever discovered.
This fossil is believed to be the earliest placental mammal ever discovered.  

PITTSBURGH, Pennsylvania (CNN) -- A 5-inch-long tree shrew that looked more like a mouse than a man may be the earliest known member of the mammal group that includes humans, according to U.S. and Chinese scientists who have studied fossilized remains of the creature.

The tree shrew fossil, believed to be 125 million years old, was unearthed in China recently. Scientists say the tree shrew is the earliest known placental mammal, the type dominant today.

The fossil find is important because scientists who study human evolution are interested in learning how such early ancestors developed and eventually turned into other species.

In placental mammals, babies grow and are nourished inside the mother's body through an organ known as the placenta. Today, there are about 4,000 kinds of placental mammals, including humans, dogs, cats, whales and bats.

Experts believe this early mammal, which weighed less than a pound, had long claws, lived in bushes and ate insects, much like modern squirrel-like shrews. However, unlike its modern counterparts, the ancient shrew had the unfortunate task of dodging carnivorous dinosaurs.

Dr. Qiang Ji, of the Chinese Academy of Natural History, and researchers from Pittsburgh's Carnegie Museum of Natural History describe the fossil in this week's edition of the British journal Nature.

The Cretaceous period, which lasted from 144 million to 65 million years ago, was the last hurrah for the dinosaurs. At the end of the Cretacious, something -- many scientists believe it was a massive metor -- caused the extinction of the dinosaurs and most other animal species on Earth, opening the door for mammals to take over. 

Two other mammal types still survive -- marsupials, such as wallabys, kangaroos and opossums, whose offspring develop in pouches; and momotremes, which lay eggs. Only three monotremes still exist -- the duck-billed platypus and two species of spiny anteaters.

Researchers named the animal Eomaia scansoria. Eomaia is Greek for "dawn mother," and scansoria is Latin for "climber." They say the fossil is unusually well preserved.

"This mammal could be our great, great-aunt or uncle, or it could be our great-grandparent, 125 million years removed," said Dr. Zhe-Xi Luo, a vertebrate paleontologist at the Carnegie Museum.

At the time of Eiomeia, seven different types of mammals thrived. Scientists believe better understanding of this small creature and its habits, such as its ability to climb, could help explain why this type has survived for more than 100 million years while other types did not.

The fossil was unearthed in the Liaoning Province in northeastern China, which is considered a gold mine for paleontologists. Feathered dinosaurs, very primitive birds and some of the world's most important early mammals have all been found there.

Luo says the area is like a "mesozoic Pompeii," with fossils well preserved in layers of volcanic ash, which is an excellent condition for recovering them. He said Eomaia is in such good condition that a microscopic look at it actually reveals mammal hair, which is an especially critical find in establishing the first branch of the placental evolutionary tree.




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