Deltatheridium
Deltatheridium is an extinct species of metatherian. It lived in what is now Mongolia during the Upper Cretaceous, circa 80 million years ago. A study in 2022 strongly suggested that Deltatheridium was a marsupial, making it the earliest known member of this group.
It had a length of about. Its teeth indicate it was carnivorous. One specimen of Archaeornithoides might attest to an attack by this mammal, the skull bearing tooth marks that match its teeth.