Sinodelphys

Sinodelphys or "Chinese opossum" is an extinct mammal from the Early Cretaceous. To date it is the oldest marsupial fossil known, estimated to be 125 million years old. It was discovered and described in 2003 in rocks of the Yixian Formation in Liaoning Province, China, by a team of scientists including Zhe-Xi Luo and John Wible.

Fossil Record
Only one fossil specimen is known, a slab and counterslab given catalog number CAGS00-IG03. It is in the collection of the Chinese Academy of Geological Sciences.

Sinodelphys szalayi grew only 15 centimeters long and possibly weighed about 30 grams. Its fossilized skeleton is surrounded by impressions of fur and soft tissue, thanks to the exceptional sediment that preserves such details. Luo et al. (2003) inferred from the foot structure of Sinodelphys that it was a scansorial tree-dweller, like its non-marsupial contemporary Eomaia, or possibly arboreal, like the modern Flying Lemur Cynocephalus. Sinodelphys probably hunted worms and insects. Most Mesozoic marsupials have been found in North America, South America, and Asia. Most lived during the Late Cretaceous between 90-65 million years ago.

Etiology of Marsupials
The earliest known marsupial is Sinodelphys szalayi, which lived in China around 125 million years ago. This makes it almost contemporary to the earliest placental fossils, which have been found in the same area.

The discovery of Chinese marsupials appears to support the idea that marsupials reached Australia via Southeast Asia.