Metatherian origin in the Early Cretaceous?
Wang and Wang 2026 described
a new Early Cretaceous metatherian, Archetheridium (Figs 1, 2), a near-complete and articulated crushed skeleton from China.
“Metatheriais a mammalian clade that includes all mammals more closely related to marsupials than to placentals(Huxley 1880). It contains all marsupials and non-marsupial relatives.”
A large number traits appear in metatherians,
listed in the Wikipedia page. Early Cretaceous (125mya) Sinodelphys was the prior taxon considered the earliest known metatherian. In the LRT Sinodelphys is one of the most primitive marsupials, but it is not the earliest. Burrowing Docofossor is from the Early Jurassic. So are several placental multituberculates with marsupial ancestors in the LRT.
By contrast, the large reptile tree (LRT, 2340 taxa) does not recover a clade Metatheria. Instead the LRT recovers a basal dichotomy splitting monotremes from marsupials at the origin of the Mammalia. Later two clades of placentals evolved from separate marsupial ancestors.
This should have been a simple phylogenetic question
that turned into a headline superlative falsified by previously described taxa confirmed by the large reptile tree (LRT, 2340 taxa). Early Jurassic taxa, like Docofossor and multituberculates falsify the headline claim. No cladogram was published.
From the Wang and Wang 2026 abstract:
“The origin and early divergence of therians remain central questions in mammalian evolutionary history. The timing and mode of divergence between metatherians (the lineage including marsupials and their stem relatives) and eutherians remain poorly understood. The Early Cretaceous fossil record of metatherians remains sparse and is represented mainly by fragmentary dental and mandibular material. Here we describe a new deltatheroidan genus and species (Archetheridium sinense (gen. et sp. nov.) based on a partial skeleton from the Early Cretaceous Jehol Biota. This specimen represents the earliest known unequivocal metatherian. The new specimen preserves a distinctive combination of deltatheroidan dental and mandibular features, supporting its deltatheroidan affinity. This discovery indicates that the initial diversification of deltatheroidans and metatherians occurred earlier than previously suggested. The specimen provides new evidence for the early establishment of metatherian dental morphology and faunivorous specialization during the Early Cretaceous. Together with other records of early therians in Asia, this finding supports the hypothesis that Asia may have been a centre of metatherian origin.”
The authors considered their find a deltatheroidan, close to Deltatheroides.
Archetheridium will be added to the LRT in a day or so.
References
Wang H-B and Wang Y-Q 2026. Metatherian origin in the Early Cretaceous. Mesozoic 3(3): 245-258 DOI: 10.11646/mesozoic.3.3.3
wiki/Metatheria
wiki/Archetheridium – not yet posted
Source: https://pterosaurheresies.wordpress.com/2026/09/27/metatherian-origin-in-the-early-cretaceous/
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