The Oldest Marsupial Relative: Archetheridium sinense

Publication Info:

Transcript:

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

Meet Archetheridium sinense! The new deltatheroidan metatherian from China's Jehol biota. It shared its ecosystem with last week's new dinosaur, but at 120 million years old, it could be rewriting the history of marsupials!

Episode 352

Notes:

So, what do you think about when you hear the name marsupials, huh? Kangaroos, wombats, opossums, Thylacoleo. It's Thylacoleo, isn't it, you nerd? I'm talking to myself. Anyway, how old do you think marsupials are as an entire group? Like, in the fossil record, we know they go back 50-some-odd million years to the Eocene. Probably going back into the late Cretaceous, but there aren't any hard-set true marsupial fossils that paleontologists can really like plant that timestamp on just yet. That said, the group that includes marsupials, the metatherians, dates back significantly further, with molecular data showing the origin of the group when it split off from eutherians like us being about 100 to 125 million years ago, possibly in North America, where the oldest metatherian was about 100 million years old. Keyword is was, because do you remember the weird new therizinosaur we were talking about last week? Kayrasaurus from China's Jehol Biota. Uh well, it turns out it had a little friend. Meet Archetheridium sinense. At 120 million years old, it's not a true marsupial, but it is a metatherian. And it's a fully formed metatherian both too early and in the wrong place. Because it's now the single oldest unambiguous metatherian ever discovered, beating out its American cousin by over 20 million years. Not only pushing back the origin of metatherians, but also potentially changing where they first evolved. As usual, if you want more information, here's the source.