120-Million-Year-Old Chinese Fossil May Be the Oldest Known Relative of Marsupials

A newly described deltatheroidan mammal from China may represent the oldest confirmed metatherian—a group that includes modern marsupials and their extinct relatives—ever discovered. The fossil provides new evidence that Asia played a central role in the early evolutionary split between marsupials and placental mammals.

Archeteridium sinense lived in what is now northeastern China approximately 120 million years ago, during the Early Cretaceous.

The species was part of the Jehol Biota, an ancient ecosystem renowned for exceptionally preserved fossils of mammals, early birds and feathered dinosaurs, including the recently discovered dinosaur Kailasaurus changliensis.

A rare Early Cretaceous metatherian fossil

Archeteridium sinense represents the oldest distinct metatherian known to science. Metatherians are the broader evolutionary group that includes modern marsupials, such as kangaroos and opossums, as well as their extinct relatives.

“Mammals have undergone a long history of evolutionary divergence during the Mesozoic Era, a period traditionally characterized by the ecological dominance of non-mammalian vertebrates in terrestrial ecosystems,” said paleontologists Dr. Haixi Wang and Dr. Yuanqing Wang of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences.

“The Jurassic mammalian radiation was characterized by taxonomic, morphological and ecological diversification among stem clades. Therians became an increasingly important component of Cretaceous mammalian faunas, accompanied by extensive faunal turnover and the decline of stem clades that diversified during the Jurassic.”

“Understanding the origin and early divergence of the two therian groups, eutherians and metatherians, is fundamental to understanding the assembly of modern mammalian diversity, because the basic evolutionary framework of modern therians was established early in the Cretaceous history of these clades.”

Sharp-toothed deltatheroidan from China

According to the researchers, Archeteridium sinense belonged to the metatherian group known as deltatheroidans. These mammals were likely carnivorous or insect-eating animals with sharp teeth.

The oldest deltatheroidans known before this discovery came from Early Cretaceous rocks in Oklahoma, United States. However, the group’s more diverse and better-preserved relatives were concentrated in Late Cretaceous Asia.

The Chinese fossil helps fill a major geographic and temporal gap, suggesting that deltatheroidans began diversifying earlier and farther east than scientists previously thought.

“Deltatheroidans, including the geologically oldest known Atokatheridium and Oclatheridium, were discovered in the Antlers Formation of Oklahoma,” the scientists said.

“These taxa are generally considered to be Albian or late Aptian–Albian in age—approximately 113 to 100 million years old—but the precise ages of the strata containing the associated fossils remain poorly constrained.”

Exceptional fossil preservation

The partial skeleton of Archeteridium sinense was discovered in the Jiufudang Formation at Dasanjia Village in Liaoning Province, China. The specimen is housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.

Unlike many early metatherian fossils, which consist only of a few teeth or fragments of jaw, this specimen includes a partial skull, part of the jaw, a nearly complete set of upper teeth, and portions of the limbs and vertebral column.

This unusually complete fossil provides important information about the animal’s anatomy, feeding adaptations and early metatherian evolution.

Did marsupials originate in Asia?

The discovery supports the possibility that Asia, rather than North America, was the center of origin for marsupial mammals and their close relatives. Earlier fossil discoveries had already suggested that Asia played an important role in the early evolution of therians.

“This specimen provides new evidence for the early establishment of metatherian tooth morphology and ecological specialization during the Early Cretaceous,” the authors concluded.

“Together with other records of early therians in Asia, this discovery supports the hypothesis that Asia may have been the center of origin for metatherians.”

The findings were published in the journal Mesozoic.

Read the study.

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Wang, Haibing and Wang, Yuanqing. 2026. Metatherian originated in the Early Cretaceous. Mesozoic 3 (3): 245–258. doi: 10.11646/mesozoic.3.3.3