A new species of deltatheroidan mammal from China may be the oldest confirmed ancestor of marsupials yet found, offering fresh evidence that Asia played a central role in the deep evolutionary split between marsupials and placental mammals.
The holotype of Archetheridium sinense in dorsal view. Image credit: Hai-Bing Wang & Yuan-Qing Wang, doi: 10.11646/mesozoic.3.3.3.
Archetheridium sinense lived in what is now northeastern China approximately 120 million years ago (Early Cretaceous epoch).
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 Kayrasaurus changliensis.
The animal represents the earliest unambiguous metatherian, the broader group that includes marsupials and their extinct relatives, ever recovered.
“Mammaliaforms underwent a long history of evolutionary divergence during the Mesozoic, an interval traditionally characterized by the ecological predominance of non-mammalian vertebrates in terrestrial ecosystems,” said Dr. Hai-Bing Wang and Dr. Yuan-Qing Wang, paleontologists with the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences.
“The Jurassic radiation of mammaliaforms was characterized by taxonomic, morphological, and ecological diversification among stem clades Therians became an increasingly important component of mammalian faunas in the Cretaceous, accompanying broader faunal turnover and the decline of stem clades that diversified in the Jurassic.”
“Understanding the origin and early divergence of the two therian clades, eutherians and metatherians, is fundamental to understanding the assembly of modern mammalian diversity, because the bauplan of modern therians was initially established early in the Cretaceous history of these clades.”
According to the researchers, Archetheridium sinense belonged to a metatherian group called deltatheroidans, carnivorous or insect-eating mammals with sharp, shearing teeth.
Until now, the oldest known deltatheroidans came from the Early Cretaceous rocks of Oklahoma, the United States, while the group’s more diverse and better-preserved relatives were concentrated in the Late Cretaceous Asia.
Archetheridium sinense closes much of this geographic and temporal gap, suggesting the group’s early diversification happened earlier — and farther east — than scientists had believed.
“The geologically oldest known deltatheroidans were Atokatheridium and Oklatheridium from the Antlers Formation of Oklahoma,” the scientists said.
“These taxa have generally been regarded as Albian or Late Aptian-Albian in age (113-100 million years ago), although the precise ages of the relevant fossil-bearing horizons remain poorly constrained.”
A partial skeleton of Archetheridium sinense was recovered from the Jiufotang Formation at Dasanjia village in China’s Liaoning province.
The specimen is housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.
Unlike most early metatherian fossils, which are typically limited to a handful of teeth or jaw fragments, this fossil includes a partial skull, jaws, a nearly complete set of upper teeth, and portions of the animal’s limbs and spine.
The discovery bolsters the idea that Asia — rather than North America, as some earlier fossils suggested — may have been a center of origin for marsupial-line mammals.
“The specimen provides new evidence for the early establishment of metatherian dental morphology and faunivorous specialization during the Early Cretaceous,” the authors concluded.
“Together with other records of early therians in Asia, this finding supports the hypothesis that Asia may have been a center of metatherian origin.”
The findings were published this month in the journal Mesozoic.
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Hai-Bing Wang & Yuan-Qing Wang. 2026. Metatherian origin in the Early Cretaceous. Mesozoic 3 (3): 245-258; doi: 10.11646/mesozoic.3.3.3
