A fossilized mammal discovered in northeast China is possibly the ancestor of modern placental mammals including human beings, say scientists.

The fossil, dating back more than 130 million years ago, has been identified as the world's earliest-known eutherian mammal fossil, according to joint research by Chinese and U.S. scientists.

The new discovery has pushed back the history of placental mammals 15 million years earlier than the previously oldest evidence represented by isolated teeth found in Siberia, said Xinhua news agency.

The study of the fossil by an international team of scientists from the Chinese Academy of Geological Sciences and the American Carnegie Museum of Natural History was published in the prestigious British science journal "Nature" yesterday.

The mammal has been named Eomaia scansoria, Greek for "mother of all placental mammals." Ji Qiang, chief researcher from the Chinese Academy of Geological Sciences, said that the origin of the placental mammals was an important part of the history of vertebrate life. The earliest fossil records of eutherian mammals are extremely important for understanding of the origins and early evolution of all placental mammals.

Scientists say placental mammals are the most prominent mammals in the world today. They include rats, squirrels, rabbits, elephants, horses, lions, tigers, pandas, pigs, sheep, dolphins, whales, as well as humans and other primates.

"The fossilized Eomaia is represented by an unusually complete skeleton exquisitely preserved. Around the skeleton are well preserved impressions of mammalian fur and a halo of carbonized soft-tissues," said Ji.

The skeleton of Eomaia is about 14cm long, with an estimated weight between 200 and 250 grams. Its teeth have many features of eutherian mammals.

"These features indicate that Eomaia looked like today's mouse, and was capable of climbing and scurrying on the uneven surface of the ground and had adapted to climbing the lower branches of the trees and bushes," said Ji.

Zhang Jianping, another scientist participating in the study from the China University of Geosciences, said that Eomaia was covered by the ash after a volcanic eruption and well preserved through years of history.

He said that the earth was dominated by dinosaurs more than 130 million years ago. The warm-blooded mammals are more capable of adapting to different environments. That is the reason why the placental mammals survived and prospered after the extinction of dinosaurs.

(eastday.com April 26, 2002)