Remains of Oldest Marsupial Found in China

Dec. 11 -- The fossil of a tiny creature found inNortheast China is helping scientists determine when mammals splitinto different groups: those with babies that develop inside theirmothers and those that raise their offspring in pouches.

The two groups make up more than 99 percent of all mammalstoday, and the new fossil evidence indicates the separation beganin Asia about 125 million years ago.

The newly found ancient animal, named Sinodelphys szalayi, isthe earliest known marsupial, meaning an animal with a pouch. Itwas chipmunk-sized, about 6 inches long and weighed about an ounce,according to Zhe-Xi Luo of the Carnegie Museum of Natural Historyin Pittsburgh.

Its skeleton was found in 2000 in a region where researchers hadpreviously found Eomaia, a fossil believed to be among the earliestknown placental mammals, of about the same age. The discovery isreported in Friday's issue of the journal Science.

The finding of the two fossils indicates an approximate date forthe split between the placental and pouch mammals, Luo said in atelephone interview.

"All this was happening while dinosaurs dominated the world.Mammals were able to explore a different niche and able to hangon," Luo said. "Otherwise there wouldn't be any cute koala bearsto look at."

Tree Dwellers

Luo noted that Sinodelphys had hands and feet with fingers andstrong wrists well adapted to climbing, indicating it could retreatto the trees to avoid hunting dinosaurs.

The discovery also adds support for the 19th century theory ofThomas Henry Huxley that the first marsupials lived in trees.

Luo said evidence indicates that marsupials developed in Asia,spread to North America and then moved southward to South Americaand Australia. Today marsupials are most common in Australia andSouth America, with only fossil remains in the northern hemisphere.Opossums, the only marsupial in the north, are a recent immigrant.