https://phys.org/news/2018-06-ancient-mammal-ancestor-china.html

The researchers note that the remains are part of a large collection of ancient vertebrates uncovered in the area over the past 20 years—approximately 120 species from the area have thus far been identified. Most of those, they note, have been dated to the Early Cretaceous Jehol. Therian mammals, they add, are rare finds in the area. Testing of the remains has included use of both CT scans and 3-D technology as a means of identification and reconstruction of original features. The results are remarkably detailed images of bones and teeth with accompanying labeling and explanatory details.

The researchers report also that the mammal remains were those of a creature of placental lineage, but which had features consistent with marsupials. These findings indicate that Asia may not be the place of origin for marsupials. They note also that prior research has suggested that the placental and marsupial mammal divergence likely occurred during the Jurassic period. The point out that the oldest known metatherians were those found in North America and dated to approximately 110 million years ago.