Sinodelphys

Sinodelphys is an extinct mammal from the Lower Cretaceous. It is a member of the infraclass Metatheria, the group which contains modern marsupials.
To date, it is the oldest metatherian fossil known, estimated to be 125 million years old. This makes it almost contemporary to the earliest placental fossils, which have been found in the same area.
It was discovered and described in 2003 in rocks of the Yixian Formation in Liaoning Province, China, by a team of scientists. 
"Sinodelphys szalayi" grew only 15 cm (5.9 in) long and possibly weighed about 30 g (1.05 oz). 
Its fossilized skeleton is surrounded by impressions of fur and soft tissue. Rapid burial followed volcanic events, and the fine sediment preserved details. 
From its foot structure it is thought that "Sinodelphys" was a tree-dweller, like its non-marsupial contemporary "Eomaia" and modern opossums such as "Didelphis". "Sinodelphys" probably hunted worms and insects. 
Most Mesozoic metatherians have been found in North America and Asia. Most lived during the Upper Cretaceous between 90-65 million years ago.